BIBLIOGRAPHY AGNES C. PEREY, April 2012. Screening and evaluation of ...
BIBLIOGRAPHY
AGNES C. PEREY, April 2012. Screening and evaluation of sweetpotato
genotypes for water stress resistance. Benguet State University, La Trinidad,
Benguet.
Adviser: Belinda A. Tad-awan, Ph.D.
ABSTRACT
The study aimed to screen sweetpotato genotypes from various germplasm
sources for drought resistance, determine the effect of water stress on the growth
ofthe genotypes, evaluate the growth and yield of selected sweetpotato genotypes
for drought resistance under greenhouse condition, and determine the interaction
effect of sweetpotato genotypes and levels of water stress.
Forty
sweetpotatogenotypeswith varying leaf and stem characters were
exposed to two (2) levels of water stress (no stress and moderate stress) under
room temperature (27 oC).
Results showed that among the genotypes evaluated, ten best genotypes
(NSIC 23, NSIC 31, Taiwan D, JOG 11-10, JK 7-4, JK 18-4, JK 23-1, BSU #1,
MBE–SP and Inubi – CA) were observed to have drought resistant characteristics
based on plant characters such as low dropping and shedding of leaves, lowest
drought score, high recovery rating,and relative water content, small leaf area per
plant, leaf area index, vigorous plants, more roots, longer shoot length increment
and longest roots.
Screening And Evaluation Of Sweet potato Genotypes
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Ten selected sweetpotato genotypes were further evaluated for drought
resistance under greenhouse condition.
Results showed that genotype JOG 11-10 had the highest number of
stomates on the abaxial and adaxial leaf surfaces, high drought score, high
recovery rating, highest NAR at 35 DAP, longest roots, highly vigorous plants,
moderate resistance to cutworm incidence, resistance to leaf curling, bigger leaf
area and leaf area index and more number of vine cuttings that be obtained.
BSU #1 exhibited the lowest drought score, high recovery, produced
longest vine at 50 and 65 DAP, exhibited the biggest leaf area index and leaf
area, highest number of vine cuttings.
Genotype Inubi –Ca produced the highest vine length at 70 and 105 DAP,
biggest leaf area index at 35 DAP, heaviest vine and more number of vine
cuttings.
NSIC 31 exhibited the lowest drought score, highest recovery rating,
highest (NAR) at 35 and 50 DAP and heaviest roots at harvest.
JK 23-1 produced highest RWC, highest NAR at 35 and 50 DAP and
longest vines at 35 DAP.
Taiwan D exhibited more number of stomates on the leaf surface, low
drought score, highest recovery rating, high RWC, high NAR , highly vigorous
plants, shortest vine length, bigger leaf area, and moderate resistance to cutworm
Screening And Evaluation Of Sweet potato Genotypes
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and leaf curling.
Plants under severe stress were observed to have small leaf area and leaf
area index, lowest NAR medium roots, lowest recovery rating and highest
drought score.
Plants under moderate stress were noted to have small to medium leaf area
and leaf area index, heaviest roots, longest roots and highest RWC.
Genotypes, four (JOG 11-10, JK 18 - 4, Taiwan D, NSIC 23 and Inubi –
CA) under moderate stress produced highest leaf area, highest NAR and longest
roots. Based on the parameters genotypes JK 18 - 4 and JK 7 - 4 under severe
stress showed the highest drought score and lowest recovery rating.
Out of the 10 genotypes five (JOG 11-10, JK 18 - 4, Taiwan D, NSIC 23
and Inubi - Ca) were observed to have the characters for stress resistance such as
small leaf area and leaf area index, longest roots, low drought score, high
recovery rating and more vine yield.
Leaf area at 65 DAP and root weight were positively correlated to vine
yield. Conversely, drought score was negatively correlated to vine yield.
Screening And Evaluation Of Sweet potato Genotypes
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INTRODUCTION
Background of the Study
Sweet
potato(Ipomoea batatas L. Lam), is considered worldwide as an
indigenous, traditional and subsistence crop. In the Philippines, it is “popularly
known as “camote”, a versatile rootcrop, rich in carbohydrates and other nutrients.
Its roots can be boiled, fried, sweetened, processed into flour for cakes and as part
of feed formulation. Its soft shoots can be prepared as vegetable salad while the
hard stem can be used as feed for pigs, goats and other animals (Larananget al.,
2004).
Sweet potato is high in vitamins A, C, and E, B6, copper, dietary fiber,
manganese, folate, potassium and iron. Varieties with yellow to orange flesh
indicate higher beta-carotene content while those with purple flesh have high
anthocyanin content. As a rootcrop, it has better carbohydrate complex that is
good for diabetics since they are “stabilizers”, not “enhancers”
(http://newsinfo.inquirer.net/inquirerheadlines). Its protein content is half as much
as the common potato but has less sugar (Valdez, 2002).
Sweetpotatois anunder-exploited food crop that ranks fifth among the
food crops after rice, potato wheat and seventh in the world in terms of total
production (FAOSTAT, 2008). About 90% of the world’s production comes from
Asia, and the Philippines ranks fifth next to Vietnam, Indonesia, India and China
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(Huaccho and Hijmans, 2000). BAS in 2003 has recorded Leyte, Camarines Sur,
Bohol, Albay and Quezon as the top five producers of sweet potato in the country.
However,its 2004 report,Tarlac was listed to have the fifth largest hectarage of
sweet potato but has the largest contiguous commercial sweet potato area in the
Philippines (PCARRD, 2006).
Ninety percent of sweet potato produced in the Philippines is used for food,
5% for feed and another 5% for processing. The per capita consumption is only
about 18 kg per year compared to the more than 100 kg per year for rice
(FAOSTAT, 2002).
Sweetpotatois a secondary staple food crop for people living in rural areas,
hilly regions and coastal plains. In Tarlac, sweetpotato is next to rice. Production
of quality storage roots of sweetpotato is important to sustain the emerging
population in the area. However, farmers had difficulties in producing quality
storage roots during summer due to production constrains such as genotypes,
water and temperature.
Sweet potato productivity is limited by a number of both biotic and
abiotic constraints. Water stress is one of the most common environmental
stresses affecting plant growth and productivity (Boyer, 1982). Plant water stress,
often times caused by drought, can have major impacts on plant growth and
development. When it comes to crops, plant water stress can be the cause of lower
yields and possible crop failure (Onyilagha, 2008).
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The main consequence of moisture stress is decreased growth and
development caused by reduced photosynthesis. Photosynthesis is the process in
which plants combine water, carbon dioxide and light to make carbohydrates for
energy. Chemical limitations due to reductions in critical photosynthetic
components such as water can negatively impact plant growth (Farkas, 2004).
Low water availability can also cause physical limitations in plants.
Stomates are plant cells that control movement of water, carbon dioxide, and
oxygen into and out of the plant. During moisture stress, stomates close to
conserve water. This also closes the pathway for the exchange of water, carbon
dioxide, and oxygen resulting in decreases in photosynthesis. Leaf growth will be
affected by moisture stress more than root growth because roots are more able to
compensate for moisture stress (Bauder, 2009).
Drought is a worldwide problem, seriously limiting global crop
production.Recently, global climate change has made this situation more serious
(Pan, 2002). Drought is a complex physical-chemical process, in which many
biological macromolecules and small molecules are involved, such as nucleic
acids (DNA, RNA, microRNA), proteins, carbohydrates, lipids, hormones, ions,
free radicals and mineral elements (Levitt, 1979).
Sweet potato is considered to be moderately drought tolerant (Valenzuela
et al., 2000). However, drought is often a major environmental constraint for
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sweetpotato production in areas where it is grown under rainfed condition
(Anselmoet al., 1998).
Objectives of the Study
Generally, the study was conducted to screen and evaluate sweetpotato
genotypes for water stress.
The specific objectives of the study were to:
1. screen sweetpotato genotypes from various germplasm
sources for drought resistance;
2. determine the effect of water stress on the growth of
genotypes.
3. evaluate the growth and yield of selected sweetpotato
genotypes for drought resistance under greenhouse
condition;
4. determine the interaction effect of sweetpotato genotypes
and levels of water stress; and
5. correlate growth parameters with vine yield of sweetpotato
genotypes.
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Importance of the Study
Maintaining and increasing supply of food to the emerging population has
been a challenging problem to the governments because of vagaries in global
climate and the resultant effect on crop productivity. Global climate change
involves a rise in temperature, water deficit stress, high CO2, high UV radiation,
rainfall and others. All of these changes affect (beneficial or detrimental) the
production of plants that are used for food.
Considering the role that sweetpotato plays into food production and
industrial uses, it is paramount to determine genotypes that are resistant to water
stress. The information generated relative to water stress resistance can be useful
in elucidating such resistance in other crops.
Time and Place of the Study
This study was conducted at SitioBakitan, Barangay Nipaco, Paniqui,
Tarlac from May to October 2011.
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REVIEW OF LITERATURE
Importance of Sweetpotato
Sweet potato ranks third among the 10 major crops of the world on a
calorie per surface unit basis (Boukamp, 1985). It is the most productive
carbohydrates producing crop and requires less inputs and water compared to rice,
corn and potato. Sweet potato is a good alternative food supplement during the
rice shortage (Zuraida, 2003). It was reported by FAO (1999) that sweet potato
can produce more edible energy per hectare per day than wheat, rice or cassava.
Sweetpotato is excellent source of vitamin A (the more colored the sweet potato,
the more vitamin A it contains), potassium, vitamin C, vitamin B6, riboflavin,
copper, pantothenic acid and folic acid. Higher in starch than potato, it contains
more or less the same amount of carbohydrate and the nutritional information of
sweetpotato per 3.5 oz/100 g are water 73%, protein 1.6 g, fat 0.3g,
carbohydrates 24.3g, fiber 2.5g, and calories 105g (Encarta, 2007).
Water Stress Definition and Characteristics
Water stress occurs when the demand for water exceeds the available
amount during a certain period or when poor quality restricts its use. It causes
deterioration of fresh water resources in terms of quantity (aquifer over-
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exploitation, dry rivers, etc.) and quality (eutrophication, organic matter pollution,
saline intrusion, etc.)(UNEP Freshwater in Europe, 2009).
Water stress is characterized as having insufficient water of satisfactory
quality and quantity to meet human and environmental needs. While many people
are already living in regions facing water stress, it has been estimated that by
2025, the share of the world's population living in water stressed areas will
increase to 35% or about 2.8 billion people. In fact, it is predicted that, in the near
future, there may well be conflicts over water on the same scale as those for oil.
According to the Falkenmark (2001), a country or region is said to
experience "water stress" when annual water supplies drop below 1,700 cubic
meters per person per year. At levels between 700 and 1,000 cubic meters per
person per year, periodic or limited water shortages can be expected.
Definition of Drought
A field definition for drought is a period without rain, of sufficient
duration to cause injury to the crop and significantly reduce the economic yield.
Drought begins when the readily available soil water in the root zone is exhausted
(Kramer, 1983).
Drought stress is the most common adverse environmental condition that
can seriously reduce crop productivity. Increasing crop resistance to drought
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stress would be the most economical approach to improve agricultural
productivity and to reduce agricultural use of fresh water resources (Islam, 2007).
Drought is one of the most common environmental stresses affecting plant
growth and productivity (Boyer, 1982). Polyethylene glycols (PEG) of high
molecular weights have been long used to simulate drought stress in plants as
non-penetrating osmotic agents lowering the water potential in a way similar to
soil drying (Larher et al., 1993).
Drought tolerance refers to the degree to which a plant is adapted to arid
or drought conditions. Desiccation tolerance is an extreme degree of drought
tolerance. Plants naturally adapted to dry conditions are called xerophytes (Levitt,
1979).
Drought is a worldwide problem and a major proportion of agriculture
land is affected with varying degrees of drought. Water deficit, extreme
temperatures and low atmospheric humidity lead to drought, which is one of the
most limiting factors for better plant performance and higher crop yield (Szilgyi,
2003; Hirtet. al., 2003). The repercussions of water deficit include its adverse
effects on plant phenology, phasic development, growth, carbon assimilation,
assimilate partitioning and plant reproduction processes. Drought stress
differentially affects the level of endogenous phytohormones. Phytohormones are
naturally occurring organic substances, which influence physiological processes
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at low concentrations either in distant tissues to which they are transported or in
the tissue where synthesis occurred (Davies, 1995a).
Water plays a crucial role in the survival of all organisms. In plants in
particular, aside from fulfilling the roles of solvent, transport medium and
evaporative coolant, water provides the energy necessary to drive photosynthesis,
the natural plant process which synthesizes organic food. Photoautotrophs are
organisms that posses their own chlorophyll and are able to harness the energy
associated with sunlight, in a process called photosynthesis. Under drought
conditions the loss of water in the plant protoplasm may result in the
concentration of ions in the protoplasm to toxic levels resulting in possible protein
denaturation and membrane fusion and negatively impacting plant metabolism
(Ramanujam, 1985).
Water deficiency is a severe limiting factor in several countries and
impacts on both food production and the economies of these countries.
Approximately four-tenths of the world’s agricultural land is in arid or semi-arid
regions with transient droughts causing death of livestock, famine and social
dislocation. Several agricultural regions are reliant on irrigation to maintain yields.
Climate change has been implicated in the fact that drought areas have more than
doubled in the last thirty years (Somasundaram et al., 2008).
A drought tolerant plant can tolerate a period of time without water. A
drought resistant plant stores water (like a cactus), dies back or goes underground
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(like an ornamental onion) or has mechanisms to protect itself from the harsh
drying sun. Once drought resistant plants are established they can live for very
long periods of time without water( Vajrabhayaet al., 2001).
Mechanism of Drought Tolerance in Plant
Drought tolerant plants typically make use of either C4 carbon fixation or
crassulacean acid metabolism (CAM) to fix carbon during photosynthesis. Both
are improvements over the more common but more basalC3 pathway in that they
are more energy efficient. CAM is particularly good for arid conditions because
carbon dioxide can be taken up at night, allowing the stomata to stay closed
during the heat of day and thus reducing water loss (Levitt, 1979).
Many adaptations for dry conditions are structural, including the
following:Adaptations of the stomata to reduce water loss, such as reduced
numbers or waxy surfaces; water storage in succulent above-ground parts or
water-filled tubers, adaptations in the root system to increase water absorption,
and trichomes (small hairs) on the leaves to absorb atmospheric water.
Gurgel (2008) stated that the indicators to have the ability to survive
during drought condition are deep root system wherein the roots are the main
engine for meeting transpirational demand, and play an important role in
controlling plant water status to avoid drought injury and leaf blades wherein
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leaves which roll under dry conditions, exposing less leaf surface to be in contact
with dry air.
According to Jiyue (2008), the various mechanisms of drought tolerance
in plants.Plants has ways of responding on drought stress, three primary types of
drought tolerance in plants have been identified: (1) drought escape; (2) drought
tolerance of dehydration postonement with high tissue water potential; (3) drought
tolerance of dehydration tolerance with low tissue water potential. Drought
escaping plants, known as desert ephemerals, are of the ability of completing their
life cycle before a serious water stress develops, but their characteristics of
drought escape have not been discussed in this paper. The characteristics of
drought tolerating plants have been concentrated on discussing in this paper. The
main characteristics of drought tolerance in plants that have the ability of
dehydration postponement with high water potential are maintenance of water
uptaker and reduction of water loss. The main characteristics of drought tolerance
in plants which are of the ability of dehydration tolerance with low water potential
are maintenance of turgor and protoplasmic desiccation tolerance.
Save et al. (2005) stated that tolerance and avoidance mechanisms to
drought stress were studied in 6-month-old plants of Newhall orange (Citrus
sinensis (L.) Osbeck) and Ellendale tangor (orange × mandarin hybrid) (Citrus
sinensis (L) Osbeck × Citrus reticulata Blanco) during a drought/rewatering cycle
under controlled conditions. Drought stress did not promote osmotic adjustment,
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while elastic adjustment (tissue elasticity increase) was noted in stressed orange
and tangor plants. Both citrus plants showed a parallel decrease in leaf
conductance (g1) and leaf water potential (Ψ1) under water stress. Tangor plants
had a more efficient water conservative strategy than orange, based on the
characteristics of canopy architecture (lower canopy area and a more closed
canopy with leaves nearly vertically oriented) together with a significant decrease
in cuticular transpiration rates (TRc) under stress.
Mickelbart (2010) stated the leaf characteristic of drought tolerant plants.
Small leaves, leaf waxes, and minimal leaf area all lead to reduced water loss, and
therefore, drought tolerance. The large leaf areas can be detrimental to growth and
survival under conditions of water stress because there is more surface area from
which water can be lost. Therefore, drought-tolerant plants will often have small
leaves or, in the case of conifers, needles that have low surface area. While this is
generally true, there are many plants with large leaf areas that are drought-tolerant,
such as southern magnolia (Magnolia grandiflora), and sycamore (Platanus sp.).
Drought-tolerant plants often accumulate waxes on their leaves or needles.
Waxes are thought to prevent water loss and reflect light, which keeps leaf
temperature from becoming too high.
Leaf hairs (called trichomes) appear as grey or white pubescence and
reflect light and reduce water loss. While we still don’t fully understand how
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trichomes affect plant water loss, leaves that are covered with these small hairs
typically lose less water than those that do not.
According to various researchers the characteristic of drought tolerance
plant are: Aromatic foliage: The essential oils exuded from plants act like a
suntan lotion, which protects the plant from the suns rays; Waxy stems and leaves:
This coating, which can be scraped off with a fingernail, protects the plant against
the sun. Waxy plants also tend to have thick stems and leaves. Silver/grey Foliage
is usually caused by layers of white hairs on the leaf surface. These hairs reduce
water loss by reflecting the sun’s rays and holding moisture; and Hairy foliage
protect the leaves from the sun.
Techniques in Screening for Drought Resistance
Polyethylene glycol (PEG) is a polymer produced in a range of molecular
weights. In 1961 Lagerwerff et al., cited that PEG can be used to modify the
osmotic potential of nutrient solution culture and thus induce plant water deficit in
a relatively controlled manner, appropriate to experimental protocols. It was
assumed that PEG of large molecular weight did not penetrate the plant and thus
was an ideal osmoticum for use in hydroponics root medium.
During the 1970’s and 1980’s, PEG of higher molecular weight (4000 to
8000) was quite commonly used in physiological experiments to induce
controlled drought stress in nutrient solution cultures. Several papers also reported
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theoretical or measured concentration-osmotic potential relations for PEG of
different molecular weights (e.g.Money, 1989; Michel, 1983; Michel and
Kaufmann, 1973). Experience gained by users indicated that these relationships
can diverge to some extent depending on the lot or source of the specific PEG
used. It is therefore advisable to measure the actual osmotic potential of the
solution culture containing PEG.
Hsissouet al. (1994) stated that polyethylene glycol 10000 (PEG), which is
a non-toxic hydrosoluble polymer, is used in the in vitro culture medium for
drought-resistance selection. PEG stimulates water stress by reducing the free
water in the extracellular medium and the water available to the cells.
According to Munir andAftab (2009), PEG (polyethylene glycol) has
been used in vitro to induce water stress in plants. It is a non-penetrating inert
osmoticum that lowers the osmotic potential of nutrient solutions, but it is not
taken and is not phytotoxic. PEG stimulates water stress in cultured plant cells in
the same way it does in the cells of intact plants.
Sakthiveluet al. (2008)cited that polyethylene glycols (PEG) of high
molecular weights have been long used to simulate drought stress in plants as
non-penetrating osmotic agents lowering the water potential in a way similar to
soil drying. According to Hassanpanah (2010), polyethylene glycol (PEG) 6000
was used for exerting the water deficiency stress on the plantlet.
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Polyethylene glycol, a non penetrable and nontoxic osmotic, lowers the
water potential of the medium and has been used to simulate drought stress in
plants. Cells adapted to PEG caused deficit of water have been isolated in
Lycopersiconesculentum. ( Bressanet al.,1981; Handa et al.,1982, 1983).
Badianeet al.(2003) stated that effects of water deficit induced by
polyethylene glycol-6000 on some cowpea varieties showed that the lateral roots
number were reduced with 3.8 fold compared to control. Inadequate water
availability is a crucial limitation to crop growth and yield (Boyer, 1982).
Hamayunet al. (2010) mentioned that polyethylene glycol (PEG)
solutions of elevated strength (8% & 16%) were used for drought stress induction.
Drought stress period span for two weeks each at pre and post flowering growth
stage. It was observed that soybean growth and yield attributes significantly
reduced under drought stress at both pre and post flowering period, while
maximum reduction was caused by PEG (16%) applied at pre flowering time.
Kulkarni and Deshpande (2007)stated that using PEG in screening tomato
germplasm under in vitro condition decreased seedling growth with increasing
concentration of PEG indicating precise nature of the in vitro screening. Mutant
hybrid and its derivatives were observed with outstanding ability to continue root
growth under in vitro stress conditions indicating their ability to fight severe water
stress situation.
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Bayoumiet al. (2008) stated that drought stress in laboratory experiment
were induced by polyethylene glycol (PEG) (0, 15 and 25%, with three replicates)
and applied on germination of wheat genotypes seeds. The PEG induced a drop in
the shoot, root biomass and coleoptiles length which was the greatest in genotypes
3, 4 and 9, while the decrease in genotypes 1,2 and 6 was little under the various
levels from PEG. The variability of leaf proteins was analyzed by sodium dodecyl
sulphate polyacrylamide gel electrophoresis (SDS-PAGE). It is concluded that
leaf protein profiles could be useful marker in the studies of genetic variation and
classification of adapted cultivars under control and stress conditions.
Trachselet al. (2011) stated that the application of PEG 8000 in corn
plants at concentrations higher than 10% (osmotic potential of 0.14 MPa) led to
reductions in elongation rates of both lateral (kLat) and axile roots (ERAx). At
concentrations of 40% axile root growth was almost stopped completely after six
days of treatment, while lateral root growth was strongly reduced and the
application of 25% PEG8000 resulted in reductions of ERAx by 38% and 58%
compared to the well watered control for P2 and CML444, respectively. ERAx for
P1 was barely altered in response to desiccation stress, indicating physiological
tolerance of desiccation stress.
Abdel-Raheem et al. (2007) showed that using different concentrations of
PEG in the medium showed a great effect on the growth value at the end of 30
days growing period. The mass of callus and shoots regenerated directly from
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explants were evaluated after 60 days of growing on regeneration MS medium
supplemented with different concentration of PEG. The highest dry weight was
achieved when the Peto-86 explants were cultivated on MS supplemented with
75.00 gram PEG. Shoots regeneration frequency of cotyledon segment of tomato
genotype ranged from 12.00 to 82.40 %.
Mathekaet al. (2008) stated that using PEG 18-20% concentration in
maize calli was found out that selected had lower survival and regeneration
capacities than unselected calli. The survival percentages of maize calli grown in
mannitol at PEG were 0.4 and 4.2 %, respectively. Six plantlets were
regenerated from mannitol – tolerant calli, while only two plantlets were
generated from the PEG tolerant calli.
Tusharet al. (2010) studied the use of PEG – 6000, with increasing
concentration of (30, 60, 90, 120 and 150 g/l) in Jatropha seedlings to study its
effect on growth parameters. The root growth, number of secondary roots, true
leaf expansion at morphological level and palisade mesophyll height, xylem
vessel expansion at anatomical level showed drastic negative impact as compared
to control. It is worth to note that local germplasm performance was categorized
into susceptible group as compared to tolerant genotype indicating need for
genetic improvement.
According toVajrabhayaet al. (2001), the four drought tolerant RD23 rice
lines were selected from somaclonal variants arising in vitro. They had been
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selected under the drought condition for 5 generations before the progenies were
used for the experiments. After five weeks in the nutrient solution containing 150
g/L PEG6000, the six-week old drought-tolerant seedlings had approximately 4-
fold increase in total soluble sugar content, while the original drought sensitive
line had only 2.5-fold, when compared with the non-stressed plants. Proline
content was also determined in these rice lines. After five weeks of drought
treatment, nine-to fifteen-fold increase in proline content was detected in the
drought tolerant lines, while the original line had approximately five-fold increase
in proline content. These data suggested that the ability to accumulate the solute
contributes to better performance in drought-tolerance.
Govindarajet al. (2010) stated that pearl millet is one of the most
important cereals grown in drought-prone areas and is the staple grain for millions
of people in West Africa and India. Breeding for drought-prone environments is
constrained by lack of suitable selection indices of drought stress resistance. The
present study is conducted to determine the reliability of in vitro screening
method for initiating drought breeding programme. This in vitro screening
method proves to be an ideal method for screening large set of germplasm with
less efforts accurately and cost effective. This experiment was carried out with a
collection of twenty one millet genotypes including commercial varieties and
advance hybrid cultures tested in completely randomized design. Data were
recorded at five different moisture stress levels (-3, -5, -7.5, -10 bars and control)
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by using polyethylene glycol (PEG) 6000 on germination percentage, root length,
shoot length, root / shoot ratio and statistically analyzed for significant differences.
The genotypes recorded significant differences for all traits in response to various
moisture stresses. The genotype TNBH 0538 gave the good germination
percentage, root length, shoot length, and root/shoot ratio as compared with
commercial cultivars under all five moisture stresses. ICMV- 221 showed highest
resistance against moisture stress, while PT6034 showed lowest resistance. TNBH
0642 also gave the better performance under all four moisture levels for most of
the traits at seedling stage. The regression studies indicated, the osmotic stress
were the most suitable method for drought tolerance screening owing to their
highly significant relationship with declining root length (R2 = 0.991; P < 0.001)
and shoot length (R2 = 0.998; P < 0.001).
Martinez et al. (2005) stated that water stress reduced CO2 net
assimilation rates quantified in the presence of high CO2 and low O2 levels (A),
stomatal conductance and transpiration, but NaCl improved water use efficiency
of PEG-treated plants through its positive effect on A values, especially in young
leaves. PEG increased the internal Na1 concentration. The resistant cell line
accumulated higher concentration of Na1 than the PEG-sensitive one. The
complete absence of Na1 in the medium endangered the survival of both cell lines
exposed to PEG. Although Na1 by itself contributed only for a small part to OA,
NaCl induced an increase in proline concentration and stimulated the synthesis of
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glycinebetaine in response to PEG in photosynthetic tissues. Soluble sugars were
the main contributors to OA and increased when tissues were simultaneously
exposed to PEG and NaCl compared with PEG alone, suggesting that Na1 may
influence sugar synthesis and/or translocation.
Uni-green technique
Uni-green technique is a technique of screening a drought resistant plant
using Polyethylene Glycol (PEG) where in single nodes of sweetpotato were used
as planting materials and planted to a floral foam. Floral foam composition is
nontoxic, environmentally friendly, has improved absorption/adsorption and
retention of liquids, is not as hard as prior art foams, does not include
polymerization by-products detrimental to flower and plant life, and is a foamed
mixture of a caustic silicate solution derived from the caustic digestion of rice hull
ash having diffused activated carbon particles from thermal pyrolysis of rice hulls.
Concept of Soil Matric Potential or Tensiometer
The concept of Soil Matric Potential (SMP) was the water is in contact
with solid particles (e.g., clay or sand particles within soil),
adhesiveintermolecular forces between the water and the solid. The forces
between the water molecules and the solid particles in combination with attraction
among water molecules promote surface tension and the formation of menisci
within the solid matrix. Force is then required to break these menisci. The
Screening And Evaluation Of Sweet potato Genotypes
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21
magnitude of matrix potential depends on the distances between solid particles—
the width of the menisci and the chemical composition of the solid matrix.
Soil Matric Potential or moisture content of the soil was measured
through the use of irrometer (soil moisture measurement is based on the
tensionmetric method, because of the fact that the amount of water is not as
important as how difficult it is for the plant to extract it from the soil) with a unit
in centibars (cb) an instrument that operates on the tensiometer principle,
installation was done a month after planting (Tensiometerquick start guide,
2010).
Studies on Drought Tolerance in Different Crops
Water deficit is a common stress in potato production, which leads to the
tuber quality and yield reduction . Because of potato susceptibility to drought
preparing sufficient water is very important for increasing potato quality and
quantity (Hassanpanahet al., 2008).
Ferreria (2002) cited that in hot dry climates, high evaporative demand
increases crop water requirements, which may compound the sensitivity of the
crop to water stress, resulting in greater yield reductions than experienced with
similar water deficits under cooler conditions.
According to several researchers, vegetables crop water requirements
range from about 6 to 24 inches (15 to 60 cm) per season, and precise irrigation
requirements can be predicted based on crop water use and effective precipitation
Screening And Evaluation Of Sweet potato Genotypes
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22
values. Since potato has a shallow root system, normally 70 percent of the total
water uptake occurs from the upper 30 cm soil depth and 100 percent from the
upper 40 to 60 cm soil depth (FAO, 2001).
King and Stark (2004) noted that water is necessary after emergence,
early vegetative stage when stolon and tubers are formed up to tuber
enlargement while Ferreria (2002) stressed that potato should be irrigated as
even as possible, particularly at 4 to 9 weeks after emergence when the tubers
are forming to avoid tuber skin cracking and malformation. Nimahet al. (2000)
stated that irrigation below 53% evapotranspiration (ET) causes a reduction in
non- marketable tubers as well as physiological abnormalities.
Al-Taisan (2010) stated that water stress due to drought and salinity is
probably the most significant abiotic factor limiting plant and also crop growth
and development. Salinity and drought stresses are physiologically related,
because both induce osmotic stress and most of the metabolic responses of the
affected plants are similar to some extent. Water deficit affects the germination of
seed and the growth of seedlings negatively. Temperature is an exceedingly
important factor in seed germination. It directly affects whether a plant can sprout
and, if so, how long it will take to emerge from the ground.
Saraswatiet al. (2003) cited that sweetpotatoplant’s biomass, main stem
length, internode length and diameter, leaf number and area, and root weight
Screening And Evaluation Of Sweet potato Genotypes
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23
decreased and leaf water potential decreased significantly in response to water
stress.
MFAI (2006) mentioned that yield is greatest when soil moisture is
maintained above 65% of the soil available water capacity because more tubers
are set and therefore, tuber set is particularly sensitive to moisture stress.
Likewise, several studies showed that water stress during tuber set and early
bulking growth stages causes the greatest reductions in tuber yield and quality
since few but larger tubers are produced while dry soil conditions in later stage
reduces yield and specific gravity, shortens dormancy (ICPRE and UI-CALS,
2002) and increases reducing sugar content of tubers (ICPRE and UI-CALS,
2002 )
Jose et al. (2008) cited that potato clones with high leaf number at 40
DAP, less vines at 55 DAP, early bulking ability, high harvest index and good
canopy cover were high yielding under drought condition.
Varietal Evaluation of Crops for Drought Resistance
Potato
Yadavet al. (2003) studied the effect of irrigation on growth and yield of
potato cv. Kufri Sutlej. Data revealed significant difference in the plant height due
to irrigation levels and maximum reduction in plant height was observed at CPE
of 100 mm in both years comparedto other treatments.
Screening And Evaluation Of Sweet potato Genotypes
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24
Vegetables
Upretiet al. (2000) studied the response of pea cultivars to water stress.
The results revealed that pea cultivars differed widely in vigour under the
conditions of moisture stress. There was significant reduction in plant height in all
the cultivars and the effect of moisture stress was more pronounced at vegetative
stage than at flowering stage.
Hegde (1988) studied the effect of irrigation regimes on growth of sweet
pepper. Data revealed that when the soil matric potential reached -85 kPa plant
height reduced significantly during both years of 1984 and 1985 (42.1 and 40.8
cm, respectively) as compared to those irrigated between -25 to -65 kPa which
were on par among themselves.
Kushwahaet al. (2003) studied the drought tolerance in chickpea
genotypes. They reported, general reductions in plant height in all the genotypes
under rainout shelter conditions as compared to rainfed condition, which indicated
higher intensity of stress realization in rainout shelter. Maximum reduction in
plant height was noticed in BG-362 (- 18.00) and ICC-4958 (-17.00).
Rana and Kalloo (1989) studied the morphological attributes associated
with the adaptation under water deficit condition in tomato. Data revealed that,
resistant genotype L. pimpinellifoliumrecorded highest plant height (140 cm)
compared to other resistantgenotypes, where as susceptible genotype, KS-54 had
recorded least plant height (49.60 cm). When plants were watered biweekly there
Screening And Evaluation Of Sweet potato Genotypes
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25
was significant reduction in the plant height (18.90 cm) compared to daily
watering (38.50 cm) as reported by Milton et al. (1992) in tomato.
Rad and Sree Vijay (1991) studied the moisture stress effect at different
morphological stages on growth and yield of tomato cultivars. They reported that,
different genotypes responded variedly for plant height under moisture stress.
Moisture stress at all the stages i.e., vegetative stage, 50 per cent flowering stage
and fruiting stage reduced plant height very significantly. Moisture stress imposed
at vegetative growth stage resulted in maximum reduction in plant height (68.56
cm) when compared to control (86.08 cm).
Subramanian et al. (1993) while, studying the influence of moisture
regimes on growth of brinjal, reported significant differences in the plant height at
different growth intervals. Maximum reduction was observed at the IW/CPE ratio
of 0.4 at all growth stages compared to other irrigation regimes while,
significantly higher plant height was observed in the irrigation regime of 1.0
IW/CPE ratio at all the growth stages. Differential irrigation levels revealed
reduction in the plant height in brinjal. Maximum plant height was recorded at 1.2
evapo-transpiration (59.8cm) compared to other treatments and minimum was
recorded in 1.0 evapo-transpiration (50.2 cm) as reported by Manjunathaet al.
(2004) in brinjal.
Screening And Evaluation Of Sweet potato Genotypes
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26
Subramanian et al. (1998) concluded that, irrigation at 0.90 IW/CPE ratio
responded positively and registered significantly higher plant height in chilli as
compared to other irrigation levels of 0.75, 0.60 and 0.40 IW/CPE ratios.
Thakur et al. (2000) studied the effect of water deficit on growth of chilli.
They reported that due to water deficit conditions there was reduction in the plant
height and maximum reduction was observed under 75 per cent water deficit (6.0
cm) compared to control (9.1 cm).
Kushwahaet al. (2003) studied the relationship of drought tolerance with
number of branch per plant of chickpea. They reported that there was maximum
reduction in the number of branches in K-850 (23.00) and IPC-94-132 (20.50)
under rainout shelter condition compared to rainfed condition and there was no
reduction in number of braches in BG-362 under rainout shelter compared to
rainfed condition.
Gopalkrishnaet al. (1996) reported that in linseed, when irrigation level
was induced at 0.8 IW/CPE ratio up to 75 DAS resulted in significantly higher
primary braches (6.1) andwas on par with that of delayed irrigation at o.4 IW/CPE
ratio up to 75 DAS, similarly, thenumber of secondary branches were
significantly higher when irrigation was scheduled at 0.8IW/CPE ratio throughout
crop growth (20.86) and minimum was observed in irrigation at 0.4IW/CPE ratio
(16.08).
Screening And Evaluation Of Sweet potato Genotypes
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Manjunathaet al. (2004) studied the effect of irrigation schedule on
vegetative growthof brinjal and found maximum number of branches per plant at
1.2 IW/CPE ratio (10.0)compared to the minimum number observed under
IW/CPE ratio of 1.0.
Sweetpotato
In sweetpotato, clones with high leaf number at 40 DAP, less vines at 55
DAP, early bulking ability, high harvest index and good canopy cover were high
yielding under drought condition (Anselmo, 1992)
Kelm et al. (2000) stated that sweetpotato genotypes with small canopies
were associated with a consistently positive response in their final storage root dry
matter (DM) yields to increasing N supply, and with efficient allocation of DM
and N to storage roots. Genotypes with high canopy net assimilation rates (NARs)
had a high proportion of leaves exposed to the sun and high chlorophyll content in
leaves. Nitrogen stress led to increased transpiration per unit leaf area and
decreasing WUE. Decreasing WUE under N stress was due to lower total plant
DM production rather than to increased total water transpiration per plant.
Although sweetpotato can survive severe moisture stress conditions,
marketable yield is adversely affected. The variety W-119 outperformed the other
varieties during severe moisture stress, with Resisto identified as very sensitive to
moisture stress. Variety Isondlo has the ability to use water very efficiently at all
irrigation levels showing promising results regarding yield and water usage
Screening And Evaluation Of Sweet potato Genotypes
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28
effiency (WUE). Significant differences were observed in shoot development, leaf
area index, marketable yield and stomatal conductance between the varieties and
the treatments. Severe water stress resulted in closure of stoma and exhibited
dramatic decline in photosynthetic/transpiration rate. It also demonstrate a large
set of parallel changes in the morphological, physiological and biochemical
processes when the varieties were exposed to drought stress (Laurietet al., 2009)
Screening And Evaluation Of Sweet potato Genotypes
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MATERIALS AND METHODS
This study composed of two experiments, first was the screening of 40
sweetpotato genotypes using the Uni-green technique under room temperature;
and thesecond is the evaluation of ten selected genotypes for drought resistance
under greenhouse condition.
Experiment 1: Screening of Sweetpotato GenotypesUsing Uni-Green Technique
Germplasm
Forty genotypes of sweetpotato were used in this study. The genotypes
used were initially observed to have variability in their morphological
characteristics for them to have been included for the screening. The
sweetpotatogenotypes and their morphological characteristics are described in
Table 1.
Establishment of mother plants
Cuttings were planted in 8 x 8 x 14 inches polyethylene bags with sandy
loam soil and decomposed cow manure at a ratio of 2:1 v/v.
The previously planted sweetpotato cuttings whichserved as mother
plants, were raised inside the nursery. Irrigation, fertilization, pest and disease
control measures were applied to the plants for fast growth.
Screening And Evaluation Of Sweet potato Genotypes
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Screening And Evaluation Of Sweet potato Genotypes
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Screening And Evaluation Of Sweet potato Genotypes
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Screening And Evaluation Of Sweet potato Genotypes
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Experimental design and treatments
The 40 x 2 study was laid out in Completely Randomized Design (CRD)
following the involving two factors;(genotypes designated as Factor A (Table 1)
and water stress level as Factor B) and replicated three times. Ten sample plants
per replicate were considered; a total of 2,400 thus,
Factor A consisted of 40 genotypes (as earlier described in Table 1)
Factor B levelinvolved the two of water stress or soil matric potential
L1 – normal condition (20 cb)
L2 –moderate stress(60 cb)
Soil moisture potential (SMP) in centibars (cb) was measured with the use
of an irrometer, operating similarly on the tensiometer principle.
Preparation of plantingmaterials
Ten cmlong nodal cuttings or cuttings with 7 nodes with newly
developed leaves were obtained from healthy sweetpotato plants. The single node
cuttings ofsweetpotato were collected between 7:00 to 8:00 A.M. while the
tissues were still fresh.
The cuttings were washed with soap and Benomyl at the recommended
rate. and were rinsed three times using purified water.
Screening And Evaluation Of Sweet potato Genotypes
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Preparation of floral foam and single-node planting materials
Floral foam measuring 2.5 cm x 3.5 cmx 2.75 cm with a weight of 0.71 g
was used as a medium or holder. The foam contains mixture of caustic silicate
solution derived from the digestion of rice hull ash having diffused activated
carbon particles from thermal pyrolysis. Floral foams were placed in each cell of
the seedling tray. About 31.5 ml purified water was used to water each floral
foam. The weight of the floral foam after watering was 26.16 g.
Single nodes with healthy buds were obtained from sterilized nodal
cuttings of sweetpotato vines. The sterilized planting materials were planted in a
floral foam late between 4:00 to 6:00 P.M. Planted single node cutting were
maintained in a seedling tray for a month (Figure 1).
Fertilizer application
The fertilization recommendation of 20 N – 20 P2O5 - 20 K20 was used
as foliar fertilizer at a rate of 70g li -l of water.
Screening And Evaluation Of Sweet potato Genotypes
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Figure 1.Sweetpotato single nodal cuttings were one week after planting in floral
foams
Drought stress imposition
A month after planting or when the plantlets had about 7 cm of roots
and shoots with at least three nodes, the plantlets wereimmersed in purified
water with 20 mg –lof polyethylene glycol 4000 (PEG) for 5 minutes on the first
Screening And Evaluation Of Sweet potato Genotypes
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36
day of treatment. In the succeeding days, immersion was reduced to 2 minutes.
Immersion was done twice.
The data gathered were:
A. Morphological Parameters
1. Number of stomates. Leaf samples were obtained from the middle portion
of the canopy at 9:00 AM. Nail polish was slowly brushed over the surface
of the leaf, air dried and covered with scotch tape. After 20 minutes, the
scotch tape was slowly removed, taking the epidermis,then mounted on a
glass slide and observed under the microscope with installed grid of one
square cm at 40 x magnification. The stomates on the adaxial and
abaxialsurfaces were counted and described.
2. Leaf orientation. Leaf inclination was observed during the cropping period
and characterized whetherplanophyle or erectophyle.
3. Leaf reaction to moisture deficit. The leaves of the different varieties were
observed if curling, drooping or shedding as a result of moisture deficit.
4. Leaf area (cm2). At 35 days after planting, thearea per leaf was calculated
based on the Tracing Technique method of Saupe (2006). Ten selected
leaves from the bottom, middle and top portions of five samples were
obtained, tracing on a coupon band, cutout and weighed. The area per leaf
was taken using the formula:
Area per leaf (cm2) = Weight of leaf tracing (g) x Conversion factor(cm2-g-1)
Screening And Evaluation Of Sweet potato Genotypes
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Area of coupon bond (cm2)
Conversion Factor (cm2-g-1) =
Weight of coupon bond (g)
The average area per leaf was obtained by adding the leaf areas divided by
the number of traced leaves.
5. Length of roots (cm). The roots of ten plantlets were measured.
6. Number of roots. The roots produced by 10 plantlets were counted.
7. Length of shoots (cm). The shoots of the plant were measured before and
after exposing them to stress.
B. Physiological Parameters
1. Drought score. A week after the application of PEG, visual observation on
the plant canopy was recorded using the rating scale (CIP, 1991) as:
Score Description
1
No stress or all the leaves are turgid in all plants
3
30% of the leaves wilted or 30 % of the plant population is wilted
5
50% of the leaves wilted or 50% of the population is wilted
7
80% of the leaves wilted or 80% of the plant population is wilted
9
Complete wilting and death of plants.
2. Recovery rating. Upon noting the drought score, the plants were watered
and after 24 hours, recovery rating was taken using the scale by Beckman
(1980) as cited by Jose and Tad-awan (2008) as follows:
Screening And Evaluation Of Sweet potato Genotypes
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Score Description
1
No recovery
3
30% of the leaves recovered
5
50% of the leaves recovered
7
80% of the leaves recovered
9
Complete recovery of the plants
3. Relative Water Content (RWC).After 45 days from planting (DAP) 10
leaves each from two sample plant, were taken at the middle portion from
the plant canopy at about 9:00 to 10:00 A.M. and weighed immediately.
The leaves were then immersed in tap water for 4 hr to obtain the turgid
weight and oven dried at 70 oC until crispy.
Fresh weight of leaves – oven dry weight of leaves
X 100
Turgid weight of leaves –
RWC =
Oven dry weight of leaves
C. Growth Parameters
1. Percentage survival.The number of surviving plantlets was counted and
expressed in percentage using the formula:
Number of explants that survived
% Survival =
X 100
Total number of explants planted
2. Plant vigor. Plant vigor was noted 30 DAP based on the rating scale by
Coffey (1999 ) as:
Screening And Evaluation Of Sweet potato Genotypes
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Scale Description Reaction
1
Plants are weak with few stems and
Poor vigor
leaves; very pale
2
Plants are weak with few thin stem and
Less vigorous
leaves; pale
3
Plants are better than less vigorous
Moderately vigorous
4
Plants are moderately strong with robust
Vigorous
stems
5
Plants are strong with robust stems and
Most vigorous
leaves: light to dark green in color
3. Height increment (cm). Plant height was measured everyafter ten days.
Measurement was obtained from the base of the plantlets to the tip of the
leaf.
Experiment 2.Evaluation of Selected Genotypes for Drought Resistance under
Greenhouse Condition
The 10 selected sweetpotato genotypes derived from Experiment 1 were
usedto further evaluate for drought resistance under greenhouse condition. The
characteristics of the 10sweetpotatogenotypes considered drought resistant are
presented in Table 2.
Screening And Evaluation Of Sweet potato Genotypes
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Table 2. Ten genotypes selected from Experiment 1 with their morphological,
physiological and growth characteristics
RELATIVE
LENGTH
GENOTYPE
LEAF
DROUGHT
WATER
ROOT
OF
AREA
SCORE*
CONTENT
NUMBER ROOTS
(cm2)
(%)
(cm)
BSU # 1
23.97
1.00
31.48
17.00
8.30
JK 7-4
56.78
1.00
28.92
12.00
7.97
JK 18 -4
23.97
1.00
27.43
11.00
8.18
JK 23 -1
32.17
1.00
20.68
9.00
8.81
JOG 11-10
20.19
1.00
33.96
19.67
7.86
MBE-SP
92.74
1.00
43.73
8.00
10.27
NSIC- 23
32.80
1.00
32.35
10.00
7.44
NSIC- 31
101.57
1.67
29.60
7.33
5.24
Taiwan -D
26.50
1.00
30.55
9.00
7.34
UBE- CA
34.07
1.00
29.19
10.00
8.28
* Rating scale: 1-no stress; 3-30% of the leaves wilted; 5- 50% of the leaves
wilted; 7- 80% of the leaves wilted ; 9 – complete wilting
Experimental design and treatments
The 10 x 3 factor factorial in randomized complete block design
(RCBD) was usedreplicated three times with 10 samples plants per treatment.
The 10 genotypes presented in Table 2 were assigned as Factor A and three
levels of water stress were assigned as Factor B as follows:
Screening And Evaluation Of Sweet potato Genotypes
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41
Factor A – Sweetpotato Genotypes
Factor B – Level water stress
L1- control /normal (20 cb)
L2- Moderate stress (60 cb)
L3 - Severe stress (80 cb)
Crop establishment
Plantlets of selected genotypes were planted in 8 x 8 x 14 inches
polyethylene bag. Polyethylene bags were filled with 12 kg mixture of three
parts of sandy loam soil (sterilized) and one half part vermicompost. Plantlets
were irrigated after planting. To ensure growth and development of the crops,
fertilization was done using complete fertilizer (14 N -14 P205-14 K20) at 15 g
per pot in split application where 5 g was applied at planting and 10 g after one
month planting.
Drought imposition
All treatment combinations were watered regularly and evenly with two
liters of water per pot for four weeks until the crops were established.
From the initial reading of 20 cb (normal ), watering was withheld until
SMP was dropped to 60 cb and 80 cb then watering was done; to attain (60 cb
and 80 cb) 1500ml and 2100 ml of water, respectively,were added. The
procedure was repeated for several times up to one week before harvesting.
Screening And Evaluation Of Sweet potato Genotypes
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Control of insect pest, diseases
Spraying of pesticide was done once a week or as the need arised. Hand
weeding was done every two weeks.
The data gathering were:
A. Meteorological Data
1. Temperature (0C). This was taken by using a thermometer. Temperatures
were recorded inside of the improvised greenhouse.
B. Morphological Parameters
Procedures on data gathering on morphological parameters such as
number of stomates, leaf orientation and leaf reaction to moisture deficit were
described in Experiment 1.
1. Storage roots reaction to sweetpotato weevil. Roots of the different
varieties were observed for the was presence of weevil.
C. Physiological Parameters
The procedures in gathering data on physiological parameters such as
drought score, recovery rating and relative water content were describe in
Experiment 1.
1. Net Assimilation Rate (NAR). Data on leaf areas at 35, 50, and 65 days
from planting were used in the computation of NAR. Two whole plant
samples were uprooted and cleaned. Storage roots were thinly
sliced,including the stems, leaves and roots oven dried at 70oC until
Screening And Evaluation Of Sweet potato Genotypes
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43
crispy. NAR was calculated as the total dry matter production per unit
leaf area per day of growth duration (modified Gardner,1985) cited by
Jose and Tadawan (2008) as:
InW2-InW1___
NAR (g/cm2 /day) =
(T2-T1) (LA2-LA1)
Where: W = Total dry matter wt of plant samples (g)
T= Time lapse (days )
LA= Leaf area ( cm2)
In = can be located in scientific calculator
D. Growth Parameters
The procedures on gathering of growth parameters such as
plantvigor,vine length,leaf area, root weight and root length were discussed in
Experiment 1.
1. Number of vine cuttings. This was the total number of vine cuttings
2. Vine Weight. This was the total weight of vines.
3. Leaf area Index (LAI). Areas per leaf at 35 , 50 and 65 DAP were used
to calculate LAI. The average area per leaf was multiplied by the
number of expanded leaves per plant. Likewise, ground area was noted
by measuring the size of the pots. Ratio of the leaf surface to the ground
area occupied by the plant was computed as:
___leaf area(cm2)_
LAI =
Ground area (cm2)
Screening And Evaluation Of Sweet potato Genotypes
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E. Incidence of Pest and Diseases
1. Insect Pest Incidence. Insect pests were identified and observed during
the cropping period using the rating scale (CIP, 2001) as cited by Jose
andTadwan (2008).
Score Description
1
No apparent injury
2
Injury confined to youngest leaves
3
Some older leaves injured
4
Over 50% of the leaves injured
5
Over 90% of the leaves injured
2. Disease incidence. Diseases were identified and observed during the
cropping period using The scale byKemeraittet al., 1981.
Score Description
0 No
disease
1
Trace to 5% infection
2
5-15%
4
35 to 67%
5
67.5 to 100%
Screening And Evaluation Of Sweet potato Genotypes
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Statistical Analysis
All data were tabulated and analyzed using the appropriate analysis of
variance for two factor factorial in Completely Randomized Design for
Experiment 1, two factor factorial in Randomized Complete Block Design for
Experiment 2. Significance among treatment means was analyzed using the
Duncan’s Multiple Range Test (DMRT). Correlation analysis was also done.
The degree of relationship between two variables was measures using the
Pearson product moment correlation coefficient (R) which characterizes the
independence of X and Y (Amid, 2005). The coefficient R is a parameter which
can be estimated from sample data using the formula:
N ∑xy – (∑x)(∑y)
R =
[ n∑ x 2 – (∑x) 2] [ n∑ y 2 – (∑x) ] 2
Screening And Evaluation Of Sweet potato Genotypes
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RESULTS AND DISCUSSION
Experiment 1. Screening of Sweetpotato Genotypes using Uni-green Technique
Morphological Parameters
Number of Stomates on the Abaxial Portion of Leaves
Effect of genotype. Significant differences were noted on the number of
stomates on the abaxial portion of the leaves. Genotype JK-18-4 had the highest
number of stomates cm2 -1 while the least was observed in genotype UPLSP-3.
Other genotypes had stomates cm2 -1 ranging from 53 to 121.67 (Table 3).
Stomatal number is a genotype characteristic but the stomatal opening and
closing are more important to affect transpiration (Jose and Tad-awan, 2008).
Furthermore, the plant leaves lose water primarily by evaporation through the
stomata. The stomatal density depends upon plant species, and can be related to
the plant-ecotype stomata mm-1 (Rowland-Bamford et al., 1990).
Effect of water stress level. Number of stomates on the abaxial portion
of leaves was significantly affected by the level of water stress. In all genotypes,
subjecting plants to moderate stress condition increased the number of stomates.
Genotypes not stressed (20 cb) showed lesser stomates-1cm2.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
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Table 3. Number of stomates on the abaxial and adaxial leaf surface (cm2) of
the 40 sweetpotato genotypes as affected by water stress level
NUMBER OF STOMATES
ABAXIAL
ADAXIAL
GENOTYPE NO
MODERATE
NO
MODERATE
STRESS
STRESS
G-MEAN
STRESS
STRESS
G-MEAN
(20 cb)
(60 cb)
(20 cb)
(60 cb)
BSU # 1
88.00 h 97.33
h 92.67g
17.27 a-g 18.24
a-e
17.76 b-e
Bureau – N
76.00 n
79.00 o 77.50m
16.41 d-I 16.57
d-g
16.49 e-h
Haponita
112.33 c
122.33 c
117.33cd
13.49 kl 14.28
j 13.39
k
Inubi –BS
118.67 b
124.67 b
121.67b
15.44 f-k 16.13
e-I
15.79 f-I
Inubi – Ca
96.33 ef
108.33 e
102.33e
14.50 h-l 16.62
d-g 15.56
g-j
Inubi- N
70.00 p 73.00
q 71.50o
17.13 a-g 17.30
a-f
17.21 c-g
Japanese Inubi
69.33 p 73.67
q 71.50o
15.86 e-k 16.37
e-h
16.11 e-i
JK -7-4
69.67 p 88.00
klm
78.83lm
14.94 g-l 16.56
d-g
15.75 f-I
JK-18-4
136.33 a
143.67 a 140.00a
14.29 i-l 16.39
e-h
15.34 hij
JK- 23-1
81.00 kl 86.67
lm
83.83k
13.46 kl 13.87 ij 13.66
k
JO6-30-3
111.00 c 114.00
d
112.50d
14.99 g-l 15.92
e-i 15.46
hij
JOG- 11-10
116.67 b 121.67
c
119.17c
16.33 d-I 17.73
a-f
17.03 d-h
JO6-11-22
78.00 mn
82.33 n 80.17l
17.52 a-f 17.86
a-f
17.69 b-e
MBE –SP
72.67 o 120.67c
96.67g
13.62 kl 15.47
f-j
14.55 ijk
NSIC 23
62.67 s
80.67 no 71.67o
15.31 f-l 15.85
e-I
15.58 g-j
NSIC 24
68.00 pq 82.00
n 75.00n
17.26 a-g 17.47
a-f
17.36 b-f
NSIC 28
82.00 k 86.00
m
84.00k
19.49 a 19.29
ab
19.39 a
NSIC 29
66.00 qr
73.67 q 69.83op
19.00 abc 19.03
a-d
19.02 ab
NSIC 31
65.67 qr
85.67 m
75.67n
12.99 l 13.36
j 13.18
k
NSIC -31 BSU
101.00 d
104.67 f
102.83e
17.49 a-f 17.58
a-f
17.54 b-e
SG-02-06-02
85.00 ij 89.00
kl 87.00i
14.38 h-l 14.76
g-j
14.57 ijk
SG-02-13-02
85.00 g
101.67 g
93.33h
15.55 f-k 15.50
f-j
15.53 g-j
SG-02-05-01
92.00 hi
96.67 h 94.33h
16.18 d-j 16.18 e-i 16.18
e-I
SG-98-6-02
86.33 n 90.33
jk
88.33j
16.23 d-j 16.86 b-g
16.55 e-h
SG-02-07-05
76.00 n 79.00
o 77.50m
16.79 c-h 17.30
a-f
17.04 d-h
SG-03-39-01
88.00 h 91.67
ij
89.83i
16.35 d-I 16.94
b-g
16.65 e-h
SP-30-03
94.67 f 98.67
h 96.67g
18.23 a-e 18.90
a-d
18.57 a-d
Super bureau B
79.00 lm 82.00
n
80.50 l
16.22 d-j 16.76
c-g
16.49 e-h
Super Bureau –N 97.00 ef 103.00 fg
100.00f
17.39 a-g 17.7
a-f
17.55 b-e
Taiwan- D
70.00 p 74.00
q 72.00o
16.69 c-I 16.66
c-g
16.68 e-h
Taiwan- R
88.00 h
92.67 ij
90.33i
18.89 abc 19.13
abc
19.01 ab
UPLB SP 1
69.00 p 72.67
q 70.83op
16.61 c-i 17.32
a-f
16.96 d-h
UPLB SP 2
83.33 jk 87.00
lm 85.17k
13.84 jkl 14.09
hij
13.97 jk
UPLB SP 3
50.00 t 53.33
s 51.67pq
17.70 a-f 17.69
a-f
17.70 b-e
UPLB SP 4
69.00 p
73.67 q
71.33o
19.43 ab 19.58
a 19.50
a
UPLB SP 5
50.00 t
56.00 r
53.00 p
17.53 a-f 17.52 a-f
17.53 b-e
UPLB SP 6
98.00 e
107.33 e
102.67e
17.03 b-g 17.10 b-g
17.07 c-h
UPLB SP 10
88.00 h
94.00 i 91.00i
18.55 a-d 18.97
a-d
18.76 abc
UPLB SP 12
65.00 r
76.67 p
70.83op
17.28 a-g 17.41
a-f
17.35 b-f
UPLB SP 24
75.67 n
79.00 o 77.33m
15.85 e-k 16.24
e-h
16.04 e-I
L- Mean
83.26b
91.16 a
87.21
16.34b
16.84a
16.59
CV(%) =1.7
*Means with the same letters are not significantly different at 5 % level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
48
Figure 2. Number of stomates on the abaxial leaf surface of representative sweetpotato
genotypes as affected by water stress level.
Interaction effect. There was a significant interaction between the
genotypes and level of water stress on the number of stomates on the abaxial
portion of the leaves. Genotype JK 18-4 under moderate stress had the highest
number of stomatescm2 -1 and the lowest number of stomate-1cm2 was observed
from UPLSP 3 under normal condition (Figure 2).
Number of Stomates on the Adaxial Portion of Leaves
Effect of genotype. Significant differences on the number of stomates on
the adaxial portion of the leaves were noted. Genotype UPLB-SP 4 had the most
number of stomates cm2 -1 with a mean of 19.50 while the least number of
stomates- cm2 -1 was observed from genotype NSIC 31. Other genotypes had
stomates cm2 -1 ranging from 13.39 to 19.39 (Table 3). According to Gardener et
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
49
al., (1985) stomatal number and size are genotypic characters of plants and
have less effect on total transpiration than stomatal opening and closing. When
stomata open wider more water is lost especially under increased solar radiation,
high temperature and windy condition.
Effect of water stress level. Level of water stress significantly affected
the number of stomates on the adaxial portion of the leaves. Genotypes under
moderate stress (60 cb) registered a higher number of stomates cm2 -1 on the
adaxial portion of the leaves, and the genotypes under not stressed had lesser
number of stomates cm2 -1. Other genotypes had a number of stomates-1cm2
ranging from 3.36 to 19.29 (Table 3). According to Xu and Zhou (2008)
moderate water deficits had positive effects on stomatal number, but more severe
deficits led to a reduction. The stomatal size obviously decreased with water
deficit, and stomatal density was positively correlated with stomatal conductance
(gs), net CO2 assimilation rate (An), and water use efficiency (WUE).
Interaction effect. Genotypes and level of water stress significantly
affected the number of stomates on the adaxial portion of the sweetpotato leaves.
Genotype UPL-SP 4 under moderate stress (60 cb) had the highest number of
stomates cm2 -1 while the least number of stomates cm2 -1 was observed from
NSIC 31 under no stress (Figure 3).
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
50
Figure 3. Number of stomates on the abaxial leaf surface of the representative
sweetpotato genotypes as affected by water stress level.
Leaf
Characteristics
Most of the genotypes exhibited planophyle leaf orientation while
genotypes Japanese-Inube and JK 23 -1 had erectophyle leaf orientation.
Erectophyle leaf orientation was noted to be efficient in intercepting solar
radiation.
Most of the genotypes’ reaction to water deficit were shedding and
dropping. Genotypes UPLB SP 5, Taiwan N, JK 7-4 and JK 18-4 had dropping
leaves as a response to water deficit. This conforms with the study of Amthor
(2005) that dropping, shedding and curling are crop responses to high
temperature and limited irrigation to reduce transpiration.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
51
Leaf Area
Effect of genotype. Genotypes significantly different on their leaf area.
Genotype NSIC 28 had the largest leaves followed by Taiwan D while the
smallest leaves were noted from genotype Super Bureau B. Other genotypes had
leaf size ranging from 19.24 to 94.95 cm2 (Table 4). The large leaf of NSIC 28
could be a mechanism to endure drought stress. According to Del Ocampo (2002)
the capacity to form leaves and sensitivity of leaf development in response to
water stress were apparently under genetic control.
Effect of water stress level. Significant effect of level of water stress was
noted on the area per leaf at 35 days after planting (DAP). Leaf area of the
genotypes under normal condition were higher than under moderate stress (60 cb).
This could be attributed to the effect of water stress on leaf expansion. Insufficient
water supply inhibits cell division and expansion resulting in the production of
smaller leaves (ICPRE and UI-CALS, 2002; Pritchard and Amthor, 2005).
Quisenberry (1982) found that the reduced leaf area observed in the stressed
plants resulted primarily from a mitotic sensitivity to water stress.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
52
Table 4. Leaf area of the 40 sweetpotato genotypes as affected by water stress
level
LEAF AREA (cm2)
WATER STRESS LEVEL
GENOTYPE NO
MODERATE
STRESS
STRESS
G- MEAN
(20 cb)
(60 cb)
BSU # 1
75.70 d 20.19
p-s
47.95 f
Bureau – N
35.96 jk
42.27 h
39.11 gh
Haponita
63.09 f 86.42
c
74.76 c
Inubi –BS
29.65 lmo 30.28
i-m 29.97
j
Inubi – Ca
18.93 pq
23.97 n-r 21.45
m
Inubi- N
26.50 mno 20.19
p-s
23.34 m
Japanese Inubi
22.71 op
25.23 m-p
23.97 kl
JO6-30-3
26.50 mno
24.60 m-q 25.55
k
JOG- 11-10
30.28 lmo
34.07 i 32.18 I
JO6-11-22
35.96 jk
18.30 rs
27.13 k
JK -7-4
30.28 lmn 26.50
l-o 28.39
jk
JK-18-4
68.13 e
56.78 f
62.46 d
JK- 23-1
34.07 jkl
92.74 b
63.40 d
MBE –SP
26.50 mno 23.97
n-r
25.24 kl
NSIC 23
47.32 hg
32.17 i-l 39.75
g
NSIC 24
23.34 op
15.14 s 19.24
n
NSIC 28
140.68 a
88.95 bc 114.28
a
NSIC 29
30.28 lmn
15.14 s 22.71
m
NSIC 31
37.85 ij
32.80 ijk 35.33
h
NSIC -31 BSU
22.71 op 19.56
p-s
21.13 mn
SG-02-06-02
81.38 c
54.26 fg
67.82 d
SG-02-13-02
27.76 mno
20.19 p-s
23.97 klm
SG-02-05-01
32.17 klm
66.24 e
49.21 f
SG-98-6-02
84.54 bc
19.56 p-s
52.05 e
SG-02-07-05
34.07 jkl 27.76
j-o
30.91 ij
SG-03-39-01
60.56 f
18.93 qrs
39.75 g
SP-30-03
25.23 no
20.19 p-s
22.71 m
Super bureau B
17.33 q
18.93 qrs
18.13 n
Super Bureau –N
51.10 g
49.84 g
50.47 ef
Taiwan- D
88.32 b
101.57 a
94.95 b
Taiwan- R
28.39 l-o 29.65
i-n
29.02 j
UPLB SP 1
36.59 jk
33.44 ij 35.01
hi
UPLB SP 2
42.27 hi 30.28
i-m 36.27
h
UPLB SP 3
47.35 gh 26.50
l-o
36.92 h
UPLB SP 4
48.58 g 26.50
h
44.16 fg
UPLB SP 5
34.07 jkl 30.28
i-m 32.17
i
UPLB SP 6
28.39 1mno 28.39
i-o 28.39
j
UPLB SP 10
80.12 cd
73.74 d 76.93
c
UPLB SP 12
39.74 ij
27.13 k-o 33.44
hi
UPLB SP 24
38.48 ij
23.34 o-r
30.91 ij
L-Mean
43.82 a 36.73
b
CV(%)= 7.8
*Means with the same letters are not significantly different at 5 % level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
53
Figure 4. Leaf area (cm2) as affected by the interaction of sweetpotato
genotypes and water stress level
Interaction
effect. Leaf area was significantly affected by the interaction
of genotypes and level of water stress (Figure 4). Genotypes under moderate
stress condition (60 cb) had smaller leaves than the leaves of the genotypes not
stressed (20 cb). Water stress during vegetative stage inhibits both cell expansion
and division leading to reduced leaf area resulting to the production of smaller
leaves, reduce vine and root expansion, plant height, and delays canopy
development but tends to acclimate the plant to water stress (IICPRE and UI-
CALS, 2002).
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
54
Root
Length
Effect of genotype. Root length of genotypes significantly different
among the genotypes (Table 5.) Genotype JK 23-1 significantly produced the
longest roots but comparable with NSIC 23 followed by Inubi – CA. While the
shortest roots were noted from genotype NSIC 28. Root length ranged from 4.93
cm to 9.37 cm. Longest roots of the genotypes may be a mechanism to endure
water stress.
Effect of water stress level. Length of roots at harvest was significantly
affected by the level of water stress (Table 7.) Longer roots were observed from
genotypes under normal condition than genotypes under moderate stress condition
(60 cb). Trachsel et al., (2011) found that plants exposed to water stress led to
the reduction in elongation rates of lateral roots. Nejad (2011) likewise stressed
that root length, number, weight and volume decreased quite in a mild drought
stress.
Interaction
effect. Genotypes and level of water stress significantly
interacted to affect the length of roots (Figure 5). The longest roots were observed
from genotype NSIC 23 under normal condition (20 cb) while the shortest roots
were observed from genotype Inubi B under moderate stress condition (60 cb)
Thangadurai et.al., (2007) cited that many plant species are able to increase water
uptake efficiency by developing deep and extensive root system under period of
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
55
Table 5. Length of roots of the 40 sweetpotato genotypes as affected by water
stress level
ROOT LENGTH (cm)
WATER STRESS LEVEL
GENOTYPE
NO STRESS
MODERATE
G-MEAN
(20 cb)
STRESS (60 cb)
BSU # 1
8.87 de
7.86 def
8.37 b
Haponita
6.73 lmn
5.66 mn
6.20 d
Inubi –BS
5.67 o 4.19
q
4.93 f
Inubi – Ca
9.63 bc
8.18 cde
8.91 b
Inubi- N
7.33 jk
6.29 k
6.81 d
Japanese Inubi
7.23 jkl
4.82 p
6.03 e
JK -7-4
9.47 bc
7.34 gh
8.40 b
JK-18-4
9.37 cd 7.97
cde 8.67
b
JK- 23-1
11.63 a
10.27 a
10.95 a
JO6-30-3
6.63 n
5.24 m-p
5.94 e
JOG- 11-10
9.75 bc
8.28 cde
9.02 b
JOG-11-22
7.73 h-k
6.19 kl
6.96 d
MBE –SP
9.23 cde
8.30 bcd
8.81 b
NSIC 23
9.92 b
8.81 b
9.37 ab
NSIC 24
6.70 lmn
5.35 m-p
6.02 e
NSIC 28
5.47 o
4.30 q
4.88 f
NSIC 29
6.60 n
5.35 m-p
5.97 e
NSIC 31
9.77 bc
7.44 fgh 8.61
b
NSIC -31 BSU
6.65 n
5.14 nop
5.89 e
SG-02-06-02
6.60 lmn
5.24 m-p
5.97 e
SG-02-13-02
5.73 o
5.03 op
5.38 ef
SG-02-05-01
7.20 klm 6.29
k
6.75 d
SG-98-6-02
8.20 ghi
5.24 m-p
6.72 d
SG-02-07-05
8.37 fg
7.76 efg
8.06 bc
SG-03-39-01
7.70 ijk 6.50
jk
7.10 cd
SP-30-03
6.70 lmn 6.19
kl
6.44 d
Super bureau B
6.77 lmn
5.35 m-p
6.06 de
Super Bureau –N
6.67 mn
5.35 m-p
6.01 e
Taiwan- D
6.63 n
5.24 m-p
5.94 e
Taiwan – N
8.77 ef
7.34 gh
8.05 bc
Taiwan- R
6.73 lmn 5.56
mno
6.15 d
UPLB SP 1
7.77 hij 6.39
k
7.08 cd
UPLB SP 2
6.67 mn
5.77 lm
6.22 d
UPLB SP 3
8.00 ghi
7.34 gh
7.67 c
UPLB SP 4
8.33 fg
6.81 ij
7.57 c
UPLB SP 5
7.67 ijk 5.77
lm
6.72 d
UPLB SP 6
6.67 mn
5.35 m-p
6.01 e
UPLB SP 10
7.98 ghi
7.44 fgh
7.71 c
UPLB SP 12
8.94 de
8.49 bc
8.71 b
UPLB SP 24
8.25 fgh
7.02 hi
7.64 c
L- Mean
7.77 a
6.46 b
7.12
CV(%)= 4.2
*Means with the same letters are not significantly different at 5 % level by DMRT
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
56
Figure 5. Root length of 10 representative sweetpotato genotypes as affected
by water stress level
drought. The degree of deep rooting can be a function of the plants root
penetration ability due to the mechanical impedance of various soil types and root
morphological characteristic such as length and density.
Number of Roots
Effect of genotype. Number of roots significantly varied among the
different genotypes (Table 6). Genotype MBE- SP produced the highest number
of roots while the lowest number of roots was observed from Inubi- BS and
SG-02-06-02. Other genotypes had number of roots ranging from 5.50 to 12.00.
Effect of water stress level. Number of roots was greatly affected by level
of water stress (Table 6). Genotypes not stressed produced higher number of
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
57
roots with while the lower number of roots was observed genotypes under
moderate stress condition. Root length density decreased with decreasing soil
moisture and increasing soil mechanical impedance (Thangaraj, 1990). Nejad
(2011) found that increased water stress reduced the root weight of the plants.
Interaction
effect. Number of roots was significantly affected by the
interaction of genotypes and level of water stress (Figure 7). Generally, genotypes
under normal condition produced more number of roots except for genotypes
Taiwan –D, JK 7-4, MBE-SP and Inubi – CA which produced higher number of
roots under moderate stress condition (60 cb). Water stress sometimes stimulates
roots growth and this presumably represents a mechanism to compensate for
limited water supply (Pritchard and Amthor, 2005).
Genotypes Inubi- BS, Super Bureau N and SG-02-06-02 under moderate
stress condition produced the lowest number of roots with a mean of 4.0 cm.
Dami (1995) found in grapes that there was a reduction and slow production of
roots under water stress.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
58
Table 6. Number of roots of the 40 sweetpotato genotypes as affected by water
stress level
NUMBER OF ROOTS
WATER STRESS LEVEL
GENOTYPE
NO STRESS
MODERATE STRESS
(20 cb)
(60 cb)
G- MEAN
BSU # 1
12.00 a
19.67bcd
11.33 b
Haponita
8.00 de
7.00 gh
7.50 ef
Inubi –BS
5.00 g 4.00
j
4.50 h
Inubi – Ca
10.00bc 11.00 bc
10.50 b
Inubi- N
9.00 cd 8.00
efg
8.50 de
Japanese Inubi
7.00 ef
7.00 gh
7.00 f
JK -7-4
7.00 ef
9.00 def
8.00 e
JK-18-4
12.00 a
12.00 b
12.00 b
JK- 23-1
9.00 cd
8.00 efg
8.50 de
JO6-30-3
7.00 ef
6.00 hi
6.50 f
JOG- 11-10
11.00 ab 10.00
cd
10.50 b
JOG-11-22
6.00 gf 5.00
ij
5.50 g
MBE –SP
11.00 ab
17.00 a
14.00 a
NSIC 23
9.00 cd 9.00
def 9.00
d
NSIC 24
7.00 ef
6.00 hi
6.50 fg
NSIC 28
8.00 de
8.00 efg
8.00 e
NSIC 29
10.33 abc
7.00 gh 8.67
d
NSIC 31
11.00 ab
10.00 cd 10.50b
NSIC -31 BSU
10.00 bc 9.00
def
9.50 cd
SG-02-06-02
5.00 g 4.00
j 4.50
h
SG-02-13-02
6.00fg
5.00 ij
5.50 g
SG-02-05-01
5.00 g
4.00 j
4.50 h
SG-98-6-02
6.00 fg 5.00
ij
5.50 g
SG-02-07-05
10.00 bc
9.00 def
9.50 c
SG-03-39-01
8.00 de 7.00
gh 7.50
ef
SP-30-03
9.00 cd
8.00 efg 8.50
de
Super bureau B
7.00 ef
7.00 gh
7.00 f
Super Bureau –N
7.00 ef
4.00 j 5.50
g
Taiwan- D
6.00 fg
7.33 fgh 6.67
f
Taiwan – N
12.00 a
11.00 bc
11.50 b
Taiwan- R
8.00 de
7.00 gh 7.50
ef
UPLB SP 1
8.00 de
8.00 efg
8.00 d
UPLB SP 2
7.00 ef
6.00 hi
6.50 f
UPLB SP 3
9.00 cd
9.00 def
9.00 c
UPLB SP 4
10.00 bc 9.67
cde
9.83 c
UPLB SP 5
9.00 cd 9.00
def
9.00 c
UPLB SP 6
7.00 ef
7.00 gh
7.00 c
UPLB SP 10
7.67 def 7.00
gh
7.33 ef
UPLB SP 12
9.00 cd 7.67
fgh 8.33
de
UPLB SP 24
9.00 cd
9.00 def
9.00 d
L- Mean
8.35 a 7.86
b
CV(%)= 12.6
*Means with the same letters are not significantly different at 5 % level by DMRT
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
59
Figure 6. Number of roots as affected by the interaction of genotypes and water
stress level
Length of Shoots Before and After Water Stress Imposition
Effect of genotype. Results show significant differences among the
different genotypes on the length of shoots (Table 7). All genotypes exhibited
increased in shoot length except for Super Bureau N. The longest shoots before
imposing stress were observed from genotype JK18- 4 and shortest shoots were
obtained from Super Bureau B.
The longest shoots after stress imposition were observed from genotype
UPLB SP 2 and the shortest shoots were measured from genotype Taiwan D.
Reduced shoot growth could be a mechanism of crops to endure water stress.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
60
Table 7. Shoot length before and after exposing to drought of the 40 sweetpotato
genotypes as by affected by water stress level
SHOOTS LENGTH (cm)
LEVEL OF WATER STRESS
NO STRESS
MODERATE
GENOTYPE
(20 cb)
STRESS (60 cb)
BEFORE
AFTER
INCREMENT
BEFORE
AFTER
INCREMENT
BSU # 1
18.87 b
21.43 d
2.56
16.83 d 19.10
cd 2.27
Haponita
15.28 h
18.14 gh
2.86
15.22 g 16.46
h 1.24
Inubi –BS
14.11 jk 17.40
I
3.29
14.05 I 15.29
klm 1.24
Inubi – Ca
15.20 h
16.80 j
1.60
13.11 lm 14.09
opq 0.98
Inubi- N
11.78 q
12.56 pq
0.78
8.87 t 11.97
st 3.10
Japanese Inubi
14.27 jk
17.53 hi
3.26
12.69 n 14.17
opq 1.48
JK -7-4
11.69 q
14.33 n
2.64
19.49 b 19.59
d 0.10
JK-18-4
20.47 a
23.29 b
2.82
18.03 c 19.92
b 1.89
JK- 23-1
14.28 jk
15.82 kl
1.54
13.00 m 13.89
pqr 0.89
JO6-30-3
15.03 h
18.16 gh
3.13
13.31 kl 16.17
hi 3.40
JOG- 11-10
14.38 j
17.96 ghi
3.58
12.10 o 15.57
i-m 3.47
JOG-11-22
15.59 g
18.44 fg
2.85
14.47 h 15.84
ijk 1.37
MBE –SP
18.03 c 19.67
e
1.64
16.74 de 17.81
f 1.07
NSIC 23
13.98 k
15.35 lm
1.37
13.58 jk 15.96
hij 2.38
NSIC 24
9.24 v
14.10 n
4.86
8.67 tu 9.66
v 0.99
NSIC 28
16.10 f
18.95 f
2.85
13.35 kl 15.55
i-m 2.20
NSIC 29
11.06 r
15.01 m
3.95
10.71 r 12.42
s 1.71
NSIC -31 BSU
14.75 I
17.92 ghi 3.17 16.33
f 18.71
de 2.38
NSIC 31
12.56 o 16.14
k
3.58
11.13 q 15.52
j-m 4.39
SG-02-06-02
12.37 no
12.81 qr
0.44
12.13 o 12.56
s 0.43
SG-02-13-02
12.87 n
13.03 op
0.16
12.58 n 13.73
qr 1.15
SG-02-05-01
13.00 mn 15.73
kl
2.73
14.83 ij 16.06
hij 1.23
SG-98-6-02 11.93
pq
13.08 op
1.15
11.04 q 13.40
r 2.36
SG-02-07-05
18.88 b
22.12 c
3.24
14.55 h 15.80
i-l 1.25
SG-03-39-01
13.19 lm 15.94
k
2.75
10.34 s 14.30
opq 3.96
SP-30-03
14.71 I
18.52 fg 3.81 15.23
g 17.29
fg 2.06
Super bureau B
6.23 x
14.03 n
7.80
8.45 u 10.79
u 2.34
Super Bureau –N
14.22 jk
16.11 k
1.89
11.78 p 14.46
nop 2.68
Taiwan D
8.72 w
11.94 r
3.22
6.17 v 6.64
w 0.27
Taiwan- N
13.42 l
16.03 k
2.61
12.05 op 15.03
mn 2.98
Taiwan- R
10.20 t
12.64 pq 2.44 10.34
s 12.04
st 1.70
UPLB SP 1
12.08 p 16.77
j
4.69
15.05 g 18.51
e 3.46
UPLB SP 2
10.08 t
24.82 a
14.12
20.36 a 21.95
a 1.59
UPLB SP 3
16.89 e
18.91 f
2.02
12.62 n 14.43
nop 1.81
UPLB SP 4
17.69 d
17.89 ghi
0.20
16.54 ef 15.48
j-m 1.06
UPLB SP 5
14.15 jk
18.34 fg
4.19
13.18 lm 17.06
g 3.88
UPLB SP 6
15.82 g
17.88 ghi
2.06
16.95 d 19.60
bc 2.65
UPLB SP 10
15.70 g
16.73 j
1.03
11.23 q 14.24
opq 3.01
UPLB SP 12
10.52 s
13.45 o
2.93
12.43 n 15.18
lm 2.75
UPLB SP 24
9.76 u
11.13 s
1.37
11.21 q 14.52
nop 3.31
L- Mean
13.74 a
16.66 a
2.92
13.24 b 15.12
b 1.88
CV(%)=
1.2
CV(%)
=2.1
*Means with the same letters are not significantly different at 5 % level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
61
Dami (1995) found that tobacco plantlets treated with PEG showed reduction in
shoot growth and lack of roots.
The highest increment in shoot length was observed from genotype NSIC
24 while the lowest increment was observed from UPLSP 3. High shoot length
increment means that genotypes may have the ability to grow faster even under
water deficit condition.
Effect of water stress level. Shoot length was significantly affected by
water stress level. The longest shoots after stress imposition were observed from
genotypes under normal condition while the shortest shoots were observed from
genotypes under moderate stress. According to Fernandez et al., (1997) there was
a consistent shoot length reduction due to drought stress.
Interaction effect. After stress imposition, shoot length significantly
different among genotypes at different water stress level (Figure 8). Genotypes
UPLB –SP 2 and JK18-4 under normal condition exhibited the longest shoots.
Shortest shoots were observed from genotype Taiwan D under moderate stress
(60 cb). This conforms with the findings of Kirnak et al. (2001) in eggplants
showing that water stress reduced both stem height and internode diameter by
46% to 51% under 40 % field capacity.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
62
Figure 7. Shoot length before water stress imposition of representative sweetpotato
genotypes as affected by water stress level.
Figure 8. Shoot length after water stress imposition of ten best genotypes as
affected by water stress level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
63
Physiological Parameters
Drought
Score
Effect of genotype. Drought score significantly differed among the
genotypes (Table 10). Lowest drought were observed in genotypes NSIC 23,
NSIC 31, Taiwan D, JOG 11-10, JK7-4, JK17-4, JK 23-1, BSU #1, MBE –SP and
Inubi- CA. Low drought score means there was no stress observed or all the
leaves were turgid in all the plants observed. This might be due to the long roots
of these genotypes which can absorb more water under limited water supply and
wide leaves to conserve moisture by covering the soil to minimize soil
evaporation.
Effect of water stress level. Significant differences in drought score as
affected by level of water stress were observed (Table 8). Lower drought score
was observed from the unstressed plants. Low drought score could be attributed
to the acculable water on a saturated soil (20 cb).
Interaction
effect. Genotypes and level of water stress interacted
significantly to affect drought score. Genotypes NSIC 23, NSIC 31, Super
Bureau N, JOG 11-10, JK 7- 4, JK-18- 4 ,JK 23-1, BSU #1, MBE –SP and
Inubi–CA subjected to moderate stress (60 cb) had the lowest drought score.
This could be attributed to the characteristic of Super Bureau B of producing roots
slowly. Salim (2010) found that shoot/root ratios consistently decrease under
drought stress, which is a universal expression of adaptation.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
64
Table 8. Drought score of the 40 sweetpotato genotypes as affected by water
stress level
DROUGHT
SCORE*
WATER STRESS LEVEL
GENOTYPE
NO STRESS
MODERATE
G-MEAN
(20 cb)
STRESS (60 cb)
BSU # 1
1.00 a
1.00 f
1.00 fg
Haponita
1.00 a
2.99 d
1.99 d
Inubi –BS
1.00 a
4.99 c
3.00 bc
Inubi – Ca
1.00 a
1.00 f
1.00 fg
Inubi- N
1.00 a
2.99 d 1.99
d
Japanese Inubi
1.00 a
2.99 d 1.99
d
JK -7-4
1.00 a 1.00
f
1.00 g
JK-18-4
1.00 a
1.00 f
1.00 g
JK- 23-1
1.00 a
1.00 f
1.00 g
JOG-30-3
1.00 a
2.99 d 1.99
d
JOG- 11-10
1.00 a
1.00 f
1.00 g
JOG-11-22
1.00 a
4.99 c
2.99 c
MBE –SP
1.00 a
1.00 f
1.00 g
NSIC 23
1.00 a
1.00 f 1.00
g
NSIC 24
1.00 a
4.99 c 2.99
c
NSIC 28
1.00 a
2.99 d 1.99
d
NSIC 29
1.00 a
4.99 c 2.99
c
NSIC 31
1.00 a
1.00 f 1.00
g
NSIC -31 BSU
1.00 a
2.99 d
1.99 d
SG-02-06-02
1.00 a 2.99
d 1.99
d
SG-02-13-02
1.00 a
2.99 d
1.99 d
SG-02-05-01
1.00 a
2.99 d
1.99 d
SG-98-6-02
1.00 a
2.99 d 1.99 d
SG-02-07-05
1.00 a
2.99 d
1.99 d
SG-03-39-01
1.00 a
2.99 d
1.99 d
SP-30-03
1.00 a
4.99 c
2.99 c
Super bureau B
1.00 a
8.99 a 4.99
ab
Super Bureau –N
1.00 a
4.99 c 2.99
c
Taiwan- D
1.00 a
1.00 f 1.00
g
Taiwan –N
1.00 a
1.67 e 1.33
e
Taiwan- R
1.00 a 8.99
a
5.00 a
UPLB SP 1
1.00 a
6.99 b
3.99 b
UPLB SP 2
1.00 a
2.99 d 1.99
d
UPLB SP 3
1.00 a
2.99 d
1.99 d
UPLB SP 4
1.00 a
2.99 d 1.99
d
UPLB SP 5
1.00 a
2.99 d
1.99 d
UPLB SP 6
1.00 a
2.99 d
1.99 d
UPLB SP 10
1.00 a
6.99 d 3.99
b
UPLB SP 12
1.00 a
2.99 d 1.99
d
UPLB SP 24
1.00 a
4.99 c 2.99
c
L-Mean
1.00 b
3.30 a
2.15
*Rating scale: 1- no stress; 2 – 30% of the leaves wilted; 5- 50% of the leaves wilted; 7- 80% of the leaves
wilted; 9- complete wilting and death of plants.
CV(%)= 15.0
*Means with the same letters are not significantly different at 5 % level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
65
Recovery
Rating
Effect of genotype. Significant differences on the recovery rating of the
different genotypes is shown in Table 9. Generally, the different genotypes had a
complete recovery. Complete recovery from water stress may imply degrees of
resistance of the genotypes evaluated.
Effect of water stress level. Recovery rating of the plants was not affected
by water stress level. All plants recovered after 24 hr of irrigation.
Interaction effect. Genotypes and level of stress did not affect the
recovery rating although all genotypes subjected to moderate stress (60 cb) had
lower recovery rating.
Relative Water Content (RWC)
Effect
genotype. Significant difference were observed on the relative
water content of the different genotypes (Table 10). Highest RWC was recorded
from JK 23-1 but comparable with Haponita. The lowest RWC was obtained
from NSIC 28. This could be attributed to the characteristic of the leaves to
absorb more water than other genotypes. Plants were able to regain turgidity to
certain extent Laurel et al., (2009).
Effect of water stress level. Relative water content (RWC) of plants at
35 DAP was significantly affected by the level of water stress. Plants under
normal condition had lower RWC while and higher RWC was observed from
plants under moderate stress (60 cb).
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
66
Table 9. Recovery rating of the 40 sweetpotato genotypes as affected by water
stress level
RECOVERY RATING *
WATER STRESS LEVEL
GENOTYPE
NO STRESS
MODERATE
G-MEAN
(20 cb)
STRESS (60 cb)
BSU # 1
9.00 a
8.99 a 8.99
a
Haponita
9.00 a
8.99 a
8.99 a
Inubi –BS
9.00 a
8.99 a 8.99
a
Inubi – Ca
9.00 a
8.99 a
8.99 a
Inubi- N
9.00 a
8.99 a 8.99
a
Japanese Inubi
9.00 a
8.99 a
8.99 a
JK -7-4
9.00 a 8.99
a 8.99
a
JK-18-4
9.00 a
8.99 a
8.99 a
JK- 23-1
9.00 a
8.99 a 8.99
a
JO6-30-3
9.00 a
8.99 a
8.99 a
JOG- 11-10
9.00 a
8.99 a 8.99
a
JOG-11-22
9.00 a
8.99 a
8.99 a
MBE –SP
9.00 a
8.99 a 8.99
a
NSIC 23
9.00 a
8.99 a
8.99 a
NSIC 24
9.00 a 8.99
a 8.99
a
NSIC 28
9.00 a
8.99 a
8.99 a
NSIC 29
9.00 a
8.99 a 8.99
a
NSIC 31
9.00 a
8.99 a
8.99 a
NSIC -31 BSU
9.00 a
8.99 a 8.99
a
SG-02-06-02
9.00 a
8.99 a
8.99 a
SG-02-13-02
9.00 a
8.99 a 8.99
a
SG-02-05-01
9.00 a
8.99 a
8.99 a
SG-98-6-02
9.00 a 8.99
a 8.99
a
SG-02-07-05
9.00 a
8.99 a
8.99 a
SG-03-39-01
9.00 a
8.99 a
8.99 a
SP-30-03
9.00 a
8.99 a 8.99
a
Super bureau B
9.00 a
0.99 d 5.00c
Super Bureau –N
9.00 a
2.96 c 5.98bc
Taiwan- D
9.00 a
8.99 a 8.99
a
Taiwan –N
9.00 a
8.99 a 8.99
a
Taiwan- R
9.00 a 8.99
a
8.99 a
UPLB SP 1
9.00 a
8.99 a 8.99
a
UPLB SP 2
9.00 a
8.99 a
8.99 a
UPLB SP 3
9.00 a
8.99 a 8.99
a
UPLB SP 4
9.00 a
8.99 a
8.99 a
UPLB SP 5
9.00 a
8.99 a 8.99
a
UPLB SP 6
9.00 a
8.99 a
8.99 a
UPLB SP 10
9.00 a
8.32 b 8.66ab
UPLB SP 12
9.00 a 8.99
a 8.99
a
UPLB SP 24
9.00 a
8.99 a
8.99 a
L-Mean
9.00 a
8.62b
8.81
*Recovery rating : 1 – no recovery; 3- 30% of the leaves recovered ; 5 – 50% of the leaves recovered ;
7 – 80% of the leaves recovered; 9- complete recovery of the plants.
CV(%) = 1.5
Means with the same letters are not significantly different at 5 % level by DMRT
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
67
Table 10. Relative water content of the 40 sweetpotato genotypes as affected by
water stress level
RELATIVE WATER CONTENT (%)
LEVEL OF WATER STRESS
GENOTYPE NO
STRESS
MODERATE
G-MEAN
(20 cb )
STRESS (60 cb)
BSU # 1
27.66 c-i 33.96
bf 30.81 bc
Haponita
42.68 a
44.12 a 43.40 a
Inubi –BS
31.10 bcd 36.42
bc 33.76 b
Inubi – Ca
29.42 b-f
27.43 gh
28.42 cd
Inubi- N
22.76 i-n
22.82 hij 22.79 de
Japanese Inubi
28.03 b-h 31.17
d-g 29.60 cd
JK -7-4
29.97 b-e
30.55 d-g
30.26 bc
JK-18-4
27.92 b-h
28.92 fg 28.42 cd
JK- 23-1
44.31 a 43.73
a 44.02 a
JO6-30-3
25.54 e-k
33.27 c-f 29.40 cd
JOG- 11-10
32.74 bc 29.19
fg 30.97 bc
JOG-11-22
32.85 b 38.32
b 35.59 b
MBE –SP
31.03 bcd
31.48 c-g
31.25 bc
NSIC 23
20.07 l-o
20.68 ij
20.38 de
NSIC 24
20.19 l-o 20.29
ij
20.24 e
NSIC 28
19.70 mno 15.59
k 17.65 e
NSIC 29
15.87 o 23.42
hij 19.65 e
NSIC 31
31.89 bcd
32.35 c-g 32.12 b
NSIC -31 BSU
28.97 b-g 30.29
d-g 29.63 cd
SG-02-06-02
28.76 b-g
32.65 c-f
30.70 bc
SG-02-13-02
25.70 e-k
29.89 efg 27.77 cd
SG-02-05-01
27.13 d-j
32.34 c-g 29.74 cd
SG-98-6-02
25.01 e-l 29.76
efg 27.39 cd
SG-02-07-05
24.55 f-m 35.10
bcd
29.83 c
SG-03-39-01
23.84 g-n
29.14 fg
26.49 cd
SP-30-03
28.04 b-h
32.26 c-g
30.15 bc
Super bureau B
24.21 g-n
24.46 hi
24.34 d
Super Bureau –N
22.06 j-n
22.59 hij 22.33 de
Taiwan- D
28.17 b-g 29.60
efg 28.88 cd
Taiwan – N
22.54 i-n
44.61 a 33.58 b
Taiwan- R
25.65 e-k 34.45
b-e
30.05 bc
UPLB SP 1
20.35 l-o 21.74
ij 21.05de
UPLB SP 2
19.83 l-o 20.32
ij
20.08e
UPLB SP 3
21.51 k-n
21.60 ij 21.55de
UPLB SP 4
21.41 k-n 23.29
hij 22.35 de
UPLB SP 5
19.19 no 19.21
jk 19.20 e
UPLB SP 6
19.92 l-o 20.70
ij
20.31 e
UPLB SP 10
22.95 h-n
23.14 hij 23.04 de
UPLB SP 12
22.56 i-n
23.17 hij 22.86 de
UPLB SP 24
22.96 h-n
23.13 hij 23.05 de
L- Mean
25.98 b 28.68 a
CV(%) =9.6
*Means with same letters in column are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
68
Interaction
effect. Significant interaction of genotypes and level of water
stress was observed on RWC at 35 DAP (Figure 10). Genotype Super Bureau N
subjected to moderate stress had the highest RWC while the lowest RWC was
observed from NSIC 28 subjected to moderate stress. Other treatment
combinations had RWC ranging from 15.87 to 43.73%. This conforms with
the study of Rai (1989) on bush beans subjected to water deficit which showed a
significant reduction of RWC of the leaves.
Figure 9. Relative water of content (%) of representative sweetpotato
genotypes as affected by water stress level
Garg (2004) cited that genotypes under drought condition had significant
decreased in plant water potential, relative water content, rate of net photosynthesis,
contents of chlorophyll, starch, soluble protein, and nitrate reductase activity.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
69
Other Growth Parameters
Percentage
Survival
Effect of genotype. Genotypes significantly varied n their survival at 30
DAP. Out of the 40 genotypes 25 genotypes had almost 100% survival. The
lowest survival were observed from genotypes UPLB SP 10 and NSIC 24. Other
genotypes had survival percentage ranging from 91.67 to 98.33% (Table 11).
Effect of water stress level. Percent survival at 30 DAP was significantly
affected by the level of water stress. Higher survival percentage was observed
from plants under normal condition. This result conforms with the study of
Badiane et al., (2003) that inadequate water availability is crucial limitation to
crop growth and yield and thus, survival.
Interaction
effect. Genotypes and water stress level interacted
significantly on the survival percentage. All genotypes under both normal and
moderate stress (60 cb) the survival percentage ranging from 88.33 to 99.99%. It
was also observed that genotypes under moderate stress had comparable with
those genotypes not stressed.
Plant
Vigor
Effect of genotype. Plant vigor at 30 DAP of the genotypes did not differ.
All genotypes had robust stems and leaves with light to dark green in color.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
70
Table 11. Survival percentage of the 40 sweetpotato genotypes as affected by
water stress level
SURVIVAL
PERCENTAGE
(%)
WATER STRESS LEVEL
GENOTYPE
NO STRESS
MODERATE
G-MEAN
(20 cb)
STRESS (60 cb)
BSU # 1
99.99 a 99.99
a 99.99
a
Haponita
99.99 a 99.99
a 99.99
a
Inubi –BS
99.99 a 99.99
a 99.99
a
Inubi – Ca
99.99 a 99.99
a 99.99
a
Inubi- N
99.66 b 99.66
b 99.66
a
Japanese Inubi
99.99 a 96.67
c 98.33
b
JK -7-4
99.99 a 99.99
a 99.99
a
JK-18-4
99.99 a 99.99
a 99.99
a
JK- 23-1
99.66 b 99.66
b 99.66
a
JO6-30-3
99.99 a 99.99
a 99.99
a
JOG- 11-10
99.99 a 99.99
a 99.99
a
JOG-11-22
99.99 a 99.99
a 99.99
a
MBE –SP
99.99 a 99.99
a 99.99
a
NSIC 23
99.99 a 99.99
a 99.99
a
NSIC 24
89.99 e 86.67
f 88.33
d
NSIC 28
99.99 a 96.67
c 98.33
b
NSIC 29
96.67c 93.33
d 95.00
c
NSIC 31
99.99 a 96.97
c 98.33
b
NSIC -31 BSU
99.99 a 99.99
a 99.99
a
SG-02-06-02
99.99 a 99.99
a 99.99
a
SG-02-13-02
99.99 a 96.67
c 98.33
b
SG-02-05-01
99.99 a 99.99
a 99.99
a
SG-98-6-02
99.99 a 99.99
a 99.99
a
SG-02-07-05
99.99 a 99.99
a 99.99
a
SG-03-39-01
99.66 b 99.66
b 99.66
a
SP-30-03
99.99 a 99.99
a 99.99
a
Super bureau B
99.99 a 99.99
a 99.99
a
Super Bureau –N
99.99 a 99.99
a 99.99
a
Taiwan- D
99.99 a 99.99
a 99.99
a
Taiwan – N
96.67 c 93.33
d 95.00
c
Taiwan- R
99.99 a 99.99
a 99.99
a
UPLB SP 1
100.00a 100.00
a 100.00
a
UPLB SP 2
100.00a 96.67
c 98.33
b
UPLB SP 3
99.67 c 96.67
c 96.67
c
UPLB SP 4
96.67 c 93.33
d 95.00
c
UPLB SP 5
100.00 a 93.33
d 96.66
c
UPLB SP 6
99.99 a 96.97
c 98.33
b
UPLB SP 10
93.33 d 83.33
g 88.33
d
UPLB SP 12
93.33 d 90.00
e 91.67
b
UPLB SP 24
93.33 d 86.67
f 90.00
b
L-Mean
98.99 a
97.39 b
98.14
CV(%) = 0.2
*Means with same letters in column are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
71
Effect of water stress level. Plant vigor at 30 DAP was not significantly
affected by level of water stress. All plants were highly vigorous.
Interaction
effect. Plant vigor at 30 DAP was not significantly affected
by genotypes and level of water stress. All genotypes were highly vigorous.
Plant Height
Effect of genotype. Plant heights at 10 DAP were significantly different
among genotypes. Genotype JK 18-4 registered the tallest plants at 10 DAP,
while the shortest plants were observed from Taiwan R with a mean height of
5.09 cm and Super Bureau B at 20 DAP (Table 12). Other genotypes had plant
heights ranging from 5.15 to 17.00 cm.
Plant heights at 30, 40 and 50 DAP are shown in Table 13. The tallest
genotypes were observed from UPLB SP 2. Shortest plants were obtained from
Taiwan N.
Effect of water stress level. Plant heights at 10, 20, 30, 40 and 50 DAP
were significantly affected by the level of waters stress (Table 13). Plants under
normal condition produced taller plants respectively while at 30 DAP plants
under moderate stress registered the tallest plants.
Interaction effect. The interaction of genotypes and level of water stress
significantly affected the height of the plants at 10, 20, 30, 40 and 50 DAP
(Figures 11, 12, 13, 14 and 15). Genotype UPLB SP2 exposed to normal
condition registered the tallest heights.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
72
Table 12. Plant height at 10, 20, and 30 DAP of the 40 sweetpotato genotypes
as affected by level of water stress
PLANT HEIGHT (cm)
LEVEL OF WATER STRESS
GENOTYPE
NO STRESS (20 cb)
MODERATE STRESS (60 cb)
10 DAP
20 DAP
30 DAP
10 DAP
20 DAP
30 DAP
BSU # 1
9.43ab
17.96b
18.41c
8.42b-e 16.03d
18.29cd
Haponita
7.62 c-h
14.51fgh
15.51efg
7.63c-g 14.52e
15.96hij
Inubi –BS
7.01 e-k
13.35ij
14.95ghi
7.00d-k 13.32gh
14.71ln
Inubi – Ca
7.57 c-I
14.42fgh
13.43lm
6.57g-m 12.51i-l
13.54o-r
Inubi- N
5.87 j-o 11.18mn
10.78qr
4.42nop 8.41s
10.8u
Japanese Inubi
7.06 e-k 13.45ij
15.00ghi
6.36g-m 12.1j-m
13.64o-r
JK -7-4
5.84 j-o 11.12mn
12.28no
9.75ab 18.56b
16.31hi
JK-18-4
10.24 a 19.52a
19.97b
9.01abc 17.16c
19.23b
JK- 23-1
7.07e-k 13.47i-j
13.53klm
6.51g-m 12.39i-l
13.57o-s
JOG-30-3
7.51d-i 14.31fgh
14.52hij
6.64g-m 12.65h-k
15.15j-m
JOG- 11-10
7.03e-k 13.39ij
15.41e-h
6.06h-m 11.54mn
14.29mno
JOG-11-22
7.74c-h 14.72efg
15.81efg
7.20 d-j 13.71fg
15.34jkl
MBE –SP
9.01abc 17.14c
16.87d
8.39b-e 15.98d
17.47def
NSIC 23
6.99 e-k 13.31ij
13.18lm
6.76f-l 12.87hij
15.1j-m
NSIC 24
4.61 op 8.78qr
12.09no
4.26op 8.10s
9.27v
NSIC 28
8.04 b-f 15.31e
16.24der
6.7f-m 12.75h-k
14.78k-n
NSIC 29
5.57 k-p 10.63no
12.84mn
5.34l-o 10.17qr
11.77t
NSIC -31 BSU
7.34 e-j 13.9klm
15.39jkl
8.18c-f 15.58pqt
17.91n-r
NSIC 31
6.24 h-n
11.89ghi
13.8e-h
5.58k-o 10.62d
13.91cde
SG-02-06-02
6.42 g-n 12.45k
13.66i-m
6.23g-m 11.56mn
13.24p-s
SG-02-13-02
6.43 g-n
12.23kl
11.57opq
6.3g-m 12.00k-n
13.34o-s
SG-02-05-01
6.56 f-m
12.48k
13.49klm
6.93e-k 13.19ghi
15.28jkl
SG-98-6-02 5.94
j-o 11.31mn
11.18pq
5.51k-o 10.5pqr
12.64s
SG-02-07-05
9.44 ab 17.98b
18.99c
7.27d-j 13.85efg
15.23jkl
SG-03-39-01
6.54 f-n
12.46k
13.66j-m
5.2l-o 9.90qr
12.97rs
SP-30-03
7.34 e-j 14.02ghi
15.86efg
7.61c-h 14.5e
16.56ghi
Super bureau B
3.11 q 5.92s 12.00nop
4.23op 8.06s
9.99v
Super Bureau –N
7.11 e-k
13.52i
13.88jkl
5.89j-n 11.21nop
13.52o-s
Taiwan D
5.01 nop 9.52jk
10.88j-m
5.17gmno
9.86mno
11.51n-q
Taiwan- N
4.34 pq 8.3ij
10.22rs
3.07p 5.81s
6.42w
Taiwan- R
6.66 f-l 12.69pq
13.71qr
6.03i-m 11.43r
14.01tu
UPLB SP 1
6.04 i-o 11.5
lm
14.38ijk
7.53 d-i 14.33ef
17.27efg
UPLB SP 2
5.04 m-p 9.6p
21.26a
10.17a 19.37a
21.36a
UPLB SP 3
8.45 b-e 16.09d
16.27de
6.33g-m 12.05klm
13.78o-r
UPLB SP 4
8.84 a-d 16.84c
15.36e-h
7. 41d-j 15.95d
16.75fgh
UPLB SP 5
7.08 e-k 13.8hi
15.73efg
6.57g-m 12.51i-l
15.69ijk
UPLB SP 6
7.9 c-g 15.04ef
15.31fgh
8.49bcd 16.16d
18.64bc
UPLB SP 10
6.35 g-n 12.1kl
14.4ijk
5.61k-o 10.69opq
13.14qrs
UPLB SP 12
5.26 l-p 10.02op
9.82s
6.21g-m 11.82lmn
14.17nop
UPLB SP 24
5.2 l-p 9.3pq
9.51s
5.5k-o 10.67opq
13.32p-s
T- Mean
6.82 a
12.99 a 14.28b 6.60
b
12.61 b
14.50a
CV(%)=11.7
CV(%)= 3.5
CV(%) = 3.5
*Means with same letters in column are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
73
Table 13. Plant height at 40 and 50 DAP of the 40 sweetpotato genotypes as
affected by level of water stress
PLANT HEIGHT (cm)
LEVEL OF WATER STRESS
NO STRESS (20 cb)
MODERATE STRESS (60 cb)
GENOTYPE
40 DAP
50 DAP
40 DAP
50 DAP
BSU # 1
24.55c
19.91c
30.69b
21.53b
Haponita
20.69ef
16.74fgh
25.86e-h
17.53f-i
Inubi –BS
19.93f-i
15.49i-m
24.91hi
16.28ijk
Inubi – Ca
19.25hij
14.4mno
24.06ijk
15.07klm
Inubi- N
14.38pq
13.00p
17.97pq
15.19klm
Japanese Inubi
20.04f-i
14.68l-o
25.00ghi
15.71jkl
JK -7-4
16.39no
12.79p
20.49no
9.26p
JK-18-4
26.63b
20.75b
33.29b
21.91b
JK- 23-1
18.03klm
14.19no
22.53lm
14.81lm
JOG-30-3
19.36q-j
17.23def
24.2ij
19.31cde
JOG- 11-10
20.55efg
16.69f-i
25.69fgh
19.1cde
JOG-11-22
20.07f-i
16.38f-j
26.34ghi
17.17ghi
MBE –SP
22.49d
18.23cd
28.11d
19cde
NSIC 23
17.58lm
16.86fgh
21.97 lm
18.63def
NSIC 24
16.11no
10.13r
20.14o
10.99o
NSIC 28
21.66de
16.35f-j
27.07de
17.91e-h
NSIC 29
17.14mn
12.99p
21.43mn
14.2mn
NSIC -31 BSU
18.4jkl
16.99efg
23.03jkl 20.06c
NSIC 31
20.53efg
19.66b
25.66fgh
21.39b
SG-02-06-02
17.88lm
13.89op
24.22ij
14.89lm
SG-02-13-02
15.43op
14.16no
17.29qr
14.98klm
SG-02-05-01
17.99klm
16.86fgh
22.49lm
18.45d-g
SG-98-6-02 14.89p
14.45mno
18.63p
16.26ijk
SG-02-07-05
25.33c 16.01f-k
31.66c
16.78hij
SG-03-39-01
18.22j-m
15.83g-l
22.77kl
18.7def
SP-30-03
21.14ef
18.06cde
26.43ef
19.55cd
Super bureau B
16.00o
11.68q
20.01o
13.37n
Super Bureau –N
18.49jkl
15.46i-m
23.11jkl
17.4f-i
Taiwan D
18.29j-m
16.19f-k
22.86jk
18.36d-g
Taiwan- N
13.52qr
6.78s
17.03qrs
7.14q
Taiwan- R
14.4pg
12.8p
18.00pq
14.09mn
UPLB SP 1
19.18ijk
19.77b
23.97ijk
22.26b
UPLB SP 2
28.34a
22.5a
35.43a
23.63a
UPLB SP 3
21.69de
15.03k-o
27.11de
16.28ijk
UPLB SP 4
20.48efg
16.75fgh
25.6fgh
16.75hij
UPLB SP 5
20.97e-f
18.51c
26.21e-h
21.34b
UPLB SP 6
20.41fgh
20.49b
25.56fgh
22.34b
UPLB SP 10
19.2ijk
15.29j-n
24.00ijk
17.41f-i
UPLB SP 12
13.1r
16.13f-k
16.37rs
18.09e-h
UPLB SP 24
12.69r
15.68h-l
15.86s
18.04e-h
Mean 19.03
a
23.83
a 17.28 b
CV(%)=3.7
CV(%)=
3.6
*Means with same letters in column are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
74
Figure 10. Plant height at 10 DAP of 10 sweetpotato genotypes as affected by
water stress level
Figure 11. Plant height at 20 DAP of 10 sweetpotato genotypes as affected by
water stress level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
75
Figure 12. Plant height at 30 DAP of 10 sweetpotato genotypes as affected by
water stress level
Figure 13. Plant height at 40 DAP of 10 sweetpotato genotypes as affected by
water stress level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
76
Figure 14. Plant height at 50 DAP of 10 sweetpotato genotypes as affected by
water stress level
Experiment 2. Evaluation of Selected Genotypes for Drought
Resistance under Greenhouse Condition
Meteorological Data
The greenhouse air temperature during the growing period ranged from
19 0C to 43 0C (Table 14). The highest temperature was observed in July
with 43 oC, while the lowest air temperature was observed in October with 18 oC.
The high temperature of 43 0C recorded was beyond the temperature
requirement of sweetpotato. According to Romero et al., (1991), sweetpotato
plants grow with temperatures between 15oC and 35oC and that lower and higher
temperatures have detrimental effects on yield. This condition may explain the
absence of storage roots of the genotypes evaluated in this study.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
77
Table 14. Greenhouse air temperature from June to September, 2011
GREENHOUSE AIR TEMPERATURE (0C)
MONTH
MINIMUM
MAXIMUM
MEAN
June 19
40 29.5
July
20
43
31.5
August
19
42
30.5
September
19
39
29.0
October
18
38
28.0
Mean
19
40.4
Morphological Parameters
Number of Stomates on the Abaxial Portion of Leaves
Effect of genotype. Significant differences among the genotypes existed
on the number of stomates on the abaxial portion of the leaves. Genotype JOG 11-
10 had the most number of stomata-1cm2 while the least was observed from
genotype NSIC 31. Other genotypes had stomates-1cm2 ranging from 87.22 to
122.44 (Table 15).
Effect of water stress level. The number of stomates on the abaxial
portion of leaves was significantly affected by the level of water stress (Table 15).
Genotypes under moderate stress condition (60 cb) showed the most number of
stomates-1cm2 in the abaxial portion of the leaves followed by genotypes under
severe stress condition (80 cb) and genotypes under control (20 cb) condition
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
78
registered the least number of stomata cm2 -1. The plant leaves lose water
primarily by transpiration through the stomata. The stomatal density depends
upon plant species, and can be related to the plant-ecotype between 300 and 800
stomata/mm (Rowland-Bamford et al., 1990). Furthermore, there was increased in
stomatal density of rice and bean leaves, with a differential effect at abaxial
(increasing) and adaxial sides. Moreover, many studies have shown that water
deficit leads to an increase in stomatal density (McCree and Davis, 1974; Cutler et
al., 1977; Yang and Wang, 2001; Zhang et al., 2006), and a decrease in stomatal
size (Cutler et al., 1977; Quarrie and Jones, 1977; Spence et al., 1986), indicating
that stomatal density may enhance the adaptation of plant to drought (Cutler et al.,
1977; Spence et al., 1986; Martinez et al., 2007).
Interaction effect. A significant interaction of genotypes and level of
water stress on the number of stomates cm2 -1 on the abaxial portion of the leaves
of sweetpotato existed (Figure 15). Genotype JOG 11-10 under moderate stress
(50 cb) registered the most number of stomates cm2 -1 on the abaxial portion of
the leaves while genotype JK 18-4 under control condition (20 cb) had the least
Other treatment combination had the number of stomates cm2 -1 ranging from
76.00 to 130.00. This confirms with results of Xu and Zhou (2008) on wheat that
moderate water deficits had positive effects on stomatal number, but more severe
deficits led to a reduction of stomata. Further, water stress decreases mean cell
size and reduces the number of stomata per leaf (Quarrie and Jones, 1977).
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
79
Table 15. Number of stomates on the abaxial leaf surface (cm2) of the 10
sweetpotato genotypes as affected level of water stress under
greenhouse condition
NUMBER OF STOMATES
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
(20 cb)
(60 cb)
(80 cb)
G-MEAN
BSU# 1
103.67 b 122.67
d
99.00 e
108.44 c
Inubi- CA
95.00 d 119.67
e 107.67
d 107.44
cd
JK-7-1 85.00
f 126.67
c 115.33
b 109.00
c
JK-18-4 74.00
h 124.67
cd 109.00
cd 102.56 d
JK 23-1
79.00 g 96.67
h 86.00
f 87.22
gh
JOG 11-10
99.00 c 175.00
a 111.00
c 128.33
a
MBE-SP 81.00
g 109.00
g 97.00 e 95.67
f
NSIC 23
91.33 e 111.67
f 97.00
e 100.00e
NSIC 31
76.00 h 98.00
h 82.00
g 85.33
g
TAIWAN- D
117.67 a 130.00
b 119.67 a 122.44
b
L- Mean
90.17 c
121.40 a
102.37 a
104.64
CV(%) = 1.3
*Means with the same letters in a column are no significantly different at 5%
level of DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
80
Figure 15. Number of stomates on the abaxial leaf surface (cm2) as affected by
the interaction of genotypes and level of water stress.
Number of Stomates on the Adaxial Portion of the Leaves
Effect of genotype. Significant differences among the genotypes on the
number of stomates in the adaxial portion of leaves were observed. Genotype
JOG 11-10 had the most number of stomatas cm2 -1 while the least was observed
from genotype NSIC 31. Other genotypes had stomates-1cm2 ranging from 13.83
to 19.44 (Table 16).
Effect of water stress level. Number of stomates on the adaxial portion
of leaves was significantly affected by the level of water stress. Genotypes under
moderate stress (60 cb) condition showed the highest number of stomates cm2 -1
on the adaxial portion of the leaves, followed by genotypes under severe stress
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
81
Table 16. Number of stomates on the adaxial leaf surface (cm2) of the 10
sweetpotato genotypes as affected level of water stress under
greenhouse condition
NUMBER
OF
STOMATES
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
(20 cb)
(60 cb)
(80 cb)
G-MEAN
BSU# 1
16.59 b 18.40
cd 16.83
d 7.27
b
JK-7-1 14.60
d 18.97
bc 19.26
ab 7.61b
JK-18-4 11.84
f 18.70
cd 18.20
c 6.25 c
JK 23-1
12.64 e 14.50
f 14.36
f 3.83
e
JOG 11-10
15.84 bc 26.25
a 18.54
bc 20.21 a
MBE-SP 13.29
e 16.35 e 15.75
e 5.13d
NSIC 23
14.61 d 16.75
e 16.20
de 5.85cd
NSIC 31
13.01 e 14.70
f 13.69
f 3.80
e
TAIWAN D
18.83 a 19.50
b 19.98
a 9.44
b
Inubi- CA
15.20 cd
17.95 d
17.98 c
7.04
bc
L-Mean
14.6c
18.21a
17.08b
CV(%)= 2.8
*Means with the same letters in a column are not significantly different at 5 %
level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
82
(80 cb) condition while genotypes under normal (20 cb) condition registered the
least number of stomates cm2 -1.
Interaction effect. There was a significant interaction of genotypes and
level of water stress on the number of stomates cm2 -1 on the adaxial portion of the
leaves of sweetpotato. Genotype JOG 11-10 under moderate stress (60 cb)
registered the most number of stomates cm2 -1 on the adaxial portion of the
leaves while genotype JK 18-4 under normal condition (20 cb) had the least.
Other treatment combinations had number of stomates cm2 -1 ranging from 12.64
to 19.98 (Figure 16). According to Klooster and Young (2004), the stomatal
density was 29 % higher in the dry vs. wet conditions which explains the higher
number of stomates during moderate and severe condition compared to the
unstressed condition.
Fig. 16. Number of stomates on the adaxial leaf surface (cm2) as affected by
genotypes and level of water stress
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
83
Leaf Characters
Leaf Orientation. Most of the genotypes exhibited planophyle leaf
orientation while genotype JK-23-1 had erectophyle leaf orientation. Erectophyle
leaf orientation was noted to be efficient in intercepting solar radiation.
Leaf Reaction to Moisture Deficit. Leaves of all genotypes responded to
water deficit through shedding and dropping. This conforms with the study of
Noogle and Fritz (1983) that drooping and sagging of plant tissues especially
leaves known as wilting which is due to change in elastic properties of cell walls
when turgor pressure declines below a certain critical value. The leaves of some
herbaceous plants sometimes droop and sag in the afternoon during hot weather
and recover again at night.
Physiological Parameters
Drought Score
Effect of genotype. Significant differences were observed on the
drought scores of the different genotypes (Table 17). Genotype Inubi –CA
registered the lowest drought score followed by genotypes Taiwan D, NSIC 31,
and BSU # 1 with 2.56 drought score. These genotypes have comparable drought
score with Inubi – CA. Low drought score may be attributed to mechanism that
help in absorbing sufficient water to maintain leaf turgidity during water stress
condition. One mechanism could be the production of pubescence in the leaves
which was exhibited by Inubi – CA.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
84
Table 17. Drought score as affected by sweetpotato genotypes and level of
water stress under greenhouse condition
DROUGHT
SCORE*
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
MEAN
(20 cb)
(60 cb)
(80 cb
BSU# 1
1.00 a 2.33
cd 4.33
cd 2.56
bc
JK-7-1 1.67
a 4.33
b 8.33
a 4.78
ab
JK-18-4 1.67
a 6.33
a 8.33
a 5.44 a
JK 23-1
1.00 a 3.67
bc 5.67
bc
3.44
b
JOG 11-10
1.67 a 4.33
b 6.33
b 4.11
bc
MBE-SP 1.67
a 2.33
cd 7.07
ab 3.69
b
NSIC 23
1.00 a 2.33
cd 6.33
b
3.22
bc
NSIC 31
1.00 a 2.33
cd 4.33
cd 2.56
bc
TAIWAN D
1.67 a 2.33
cd 3.67
d 2.56
bc
Inubi-CA 1.00
a 1.67
d 4.33
cd 2.33bc
L-Mean
1.33 bc 3.20
b
5.87 a 3.47
*Rating scale: 1 = no stress; 3 = 30% of the leaves wilted; 5 = 50% of the leaves
wilted; 7 = 80% of the leaves wilted; 9 = complete wilting and death of plants.
CV(%) = 5.09
*Mean with the same letters are not significantly different at 5% level by DMRT.
Effect of water stress level. Significant difference was observed on the
drought score of the plants as affected by the level of water stress (Table 17).
Genotypes under severe stress (80 cb) exhibited the highest drought score of
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
85
5.87. Genotypes under moderate stress condition had comparable drought score
with plants under normal condition. It was also observed that plants in the
normal condition or sufficient water showed wilting of leaves. This could be
attributed to the high temperature (39-43 oC) inside the greenhouse.
Interaction
effect. Genotypes and level of water stress interacted
significantly to affect drought scores (Figure 13). Genotypes under normal
condition (20 cb) had the lowest score ranging from 1.00 and 1.67. High
drought score is due to the depletion of water needed for turgidity brought
about by water stress and high temperature during conduct of the study.
Figure 17. Drought score as affected by the interaction of genotypes and level
of water stress.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
86
Recovery
Rating
Effect of genotype. There were significant differences on the recovery
rating of the different genotypes (Table 18). Genotype Taiwan D had the highest
recovery rating but not significantly different with Inubi-CA. Genotypes JK 7-4,
JOG 11-10 and NSIC 31 were comparable with Taiwan D and Inubi- CA. The
lowest recovery rating was noted from MBE –SP. This conforms with the work
of Taligan and Tad-awan (2004) in potato that high recovery rating of cultivars
results after rewatering under greenhouse condition.
Effect of water level on stress. Level of water stress significantly affected
the recovery rating of the plants after rewatering. Genotypes under control
condition (20 cb) had the highest recovery rating followed by genotypes under
moderate stress condition( 60 cb) and the lowest recovery rating was observed
from genotypes under severe condition.
Interaction
effect. Significant interaction of genotypes and level of water
stress was observed on the recovery rating (Figure 18). All genotypes under
control condition (20 cb) and moderate stress condition (60 cb) had higher and
comparable recovery ratings ranging from 5.00 to 9.00 and the lowest recovery
rating was observed from genotypes under severe stress condition (60 cb). It was
also observed that genotypes Taiwan D and Inubi–CA under severe stress
condition (80 cb) had recovery ratings comparable with the control and moderate
stress condition. This could be attributed to the effect of genotypic characteristic
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
87
Table 18. Recovery rating of the 10 sweetpotato genotypes as affected by level
of water stress
RECOVERY
RATING
*
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
9.00 a 6.33
bc 3.67
c 6.33 bc
JK-7-1 9.00
a 7.67
ab 5.67
b 7.44
ab
JK-18-4 9.00
a 8.33
a 3.67
c 7.00
b
JK 23-1
9.00 a 7.00
ab 5.00 bc 7.00
b
JOG 11-10
9.00 a 7.67
ab 5.67
b 7.44
ab
MBE-SP 9.00
a 5.00
c 3.67
c 5.89
c
NSIC 23
8.33 a 7.00
ab 4.33
bc 6.56bc
NSIC 31
9.00 a 7.67
ab 5.00
bc 7.22
ab
TAIWAN D
9.00 a 8.33
a 8.33
a 8.56
a
Unubi -CA
9.00 a 8.33
a 7.67
a 8.33
a
L-Mean 8.93a
7.33 b
5.27 c
7.18
*Recovery rating : 1 = no recovery; 3 = 30% of the leaves recovered; 5 = 50%
of the leaves recovered; 7 = 80% of the leaves recovered; 9 = complete recovery
of the plants
CV(%)= 12.9
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
88
of the plants and the responses to different levels of water stress. Sweetpotato as
described by O’Sullican (2002 ) is known as a relatively drought-tolerant crop, it
will tolerate brief periods of drought stress, recovering quickly when soil moisture
is restored.
Figure 18. Recovery rating as affected by the inteaction of genotypes and level of
water stress.
Relative Water Content
Effect of genotype. Relative water content (RWC) of the different
genotypes did not differ at 35 DAP. Highest RWC was obtained from genotypes
JK- 23-1 while the lowest was observed from Inubi-CA. Other genotypes had
RWC ranging from 36.93 to 55.36 %. This could be due to the mechanism of
genotypes that can regain turgidity rapidly over other genotypes. According to
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
89
Table 19. Relative water content of the 10 sweetpotato genotypes as affected by
level of water stress
RELATIVE WATER CONTENT (%)
LEVEL OF WATER STRESS
GENOTYPE
CONTROL MODERATE
SEVERE G- MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
44.46
45.32
51.01
46.93
JK-7-1
40.81
44.42
47.65
44.29
JK-18-4
42.60
42.60
50.13
44.16
JK 23-1
50.26
54.93
85.32
63.64
JOG 11-10
40.14
41.34
44.36
41.95
MBE-SP
28.93
38.63
43.24
36.93
NSIC 23
47.44
56.97
61.69
55.36
NSIC 31
40.22
40.95
49.63
43.60
TAIWAN- D
42.91
39.27
46.91
43.03
Inubi-CA
27.49
27.87
43.07
32.81
L-Mean
40.28
43.23
52.30
45.27
CV(%)= 5.38
*Means with the same letters are not significantly different at 5% level by
DMRT.
Laure et al. (2009) plants were able to regain turgidity to certain extent and
slowly loose moisture as the stress continued until harvest.
Effect of water stress level. No significant differences were observed
among the levels of water stress on relative water content at 35 DAP (Table 9).
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90
Plants subjected to severe stress (80 cb) gave the highest RWC followed by
control (20 cb) and moderate stress (60 cb) .
Interaction effect. Results show no significant interaction of genotypes
and level of water stress on RWC at 30 DAP. Genotype JK -23-1 under severe
stress condition (80 cb) had the highest RWC while the lowest was Inubi –CA
normal condition ( 20 cb). Other treatment combinations had RWC ranging
from 37.27 to 55.34 %.
Net Assimilation Rate
Effect of genotype. Net assimilation rate (NAR) of the different
genotypes was greatly affected at 35, 50 and 65 DAP. NSIC 23 exhibited the
highest NAR followed by JK-18-4 but not significantly different with NSIC 23.
Genotype JOG 11-10 had comparable NAR with NSIC 23 and JK-18-4. The
lowest NAR was observed from genotype MBE-SP. At 70 DAP, it was observed
that most genotypes had an increased NAR except for genotype Inubi-CA.
Genotype JK 23-1 had the highest NAR with a mean 4.93 followed by JK 18-4,
but these genotypes were not significantly different.
The NAR of all genotypes at 65 DAP had increased. Genotype JK 18-4
had the highest NAR which was not significantly different with JK 7-4. JOG 11-
10, Inubi –CA and JK 23-1 had comparable NAR with JK18-4 and JK 7- 4, while
the lowest NAR was observed from genotype BSU#1. Results indicate that all
genotypes had an increased dry weight accumulation per unit area of assimilate
Screening And Evaluation Of Sweet potato Genotypes
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Table 20. Net assimilation rate (NAR ) of 10 selected sweetpotato genotypes at
35 DAP as affected by level of water stress
NET ASSIMILATION RATE (%)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
2.94
2.34
1.70
2.33d
JK-7-1 3.33
2.92
2.27
2.84c
G10- JK-18-4
4.18
3.85
3.54
3.89a
JK 23-1
3.55
2.69
2.05
2.76cd
JOG 11-10
4.11
3.76 3.18
3.69ab
MBE-SP 4.37
3.19 2.26
3.27b
NSIC 23
4.66
3.74
3.49
3.96a
NSIC 31
3.02
2.52
2.28
2.61cd
TAIWAN D
3.44
3.01
1.85
2.77cd
Inubi – CA
3.68
3.46
2.82
3.32b
Mean
3.78a
3.15b
2.54 c
3.14
CV(%) =14.1
*Means with the same letters are not significantly different at 5% level by DMRT.
per unit of time. According to Fitter and Hay (1981) net assimilation rate or the
dry matter accumulation rate per unit leaf area is one of the useful parameters on
growth analysis, which influence the increase in plant weight per unit area of
assimilatory tissue (usually leaf area: AL ) per unit of time. It was observed that
Screening And Evaluation Of Sweet potato Genotypes
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92
NAR of the genotypes increased as plants mature regardless of water stress level.
Hunt (1978) mentioned that NAR is not constant with time but show downward
drift with plant age, and the age drift is accelerated by unfavorable environment.
Genotype and dry matter gain per unit leaf surface decreases as new leaves are
added due to mutual shading. Also, NAR decreases at more than 50 days old
leaves since photosynthesis decreases (Zaag, 1992).
Effect of water stress level. Significant differences were noted on NAR
of the plants at 35, 50 and 65 DAP as affected by level of water stress (Table 20,
Table 21 and Table 22). NAR of all genotypes decreased with increasing water
stress at 35, 50 and 65 DAP. Lowest NAR was observed from genotypes under
severe stress. Based on the study of Van Heerden (2008), restricted water supply
leads to inhibition of CO2 assimilation and photosynthesis through stomatal
closure. Further, drought stress decreased leaf area duration, cumulative water
transpired, net assimilation rate (Simane et al., 1993). This may explain the
decreasing trend in the net assimilation rates of sweetpotato with increasing water
stress.
Most of the genotypes under moderate stress had an increased NAR
except for genotype Inubi-CA which did not increase in NAR from 35 up to 50
DAP . Genotypes NSIC 31 and JOG 11-10 showed a decrease in NAR with
from 35 to 50 DAP.
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Table 21. Net assimilation rate (NAR ) of the 10 sweetpotato selected genotypes
at 50 DAP as affected by level of water stress
NET ASSIMILATION RATE (%)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
3.04
2.74
1.68
4.16
JK-7-1 3.83
3.62
2.77
3.41
JK-18-4 5.27
4.85
4.56
4.89
JK 23-1
4.95
5.20
4.63
4.93
JOG 11-10
4.92
2.86
3.88
3.89
MBE-SP 4.96
4.07
3.37
4.13
NSIC 23
5.07
4.88
3.47
4.49
NSIC 31
3.39
2.01
2.47
2.62
TAIWAN D
3.63
3.39
2.10
3.04
Inubi -CA
3.41
3.46
2.82
3.23
L- Mean
4.25
3.21
3.18
6.88
CV(%) = 22.9
*Means with the same letters are not significantly different at 5% level by DMRT.
Interaction
effect. The interaction of genotypes and level of water stress
did not significantly affect the NAR at 35, 50 and 65 DAP. All genotypes
subjected to level of water stress had an increased NAR from 35 up to 65 DAP.
Screening And Evaluation Of Sweet potato Genotypes
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Table 22. Net assimilation rate (NAR ) of the 10 sweetpotato selected genotypes
at 65 DAP as affected by level of water stress
NET ASSIMILATION RATE (%)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
3.45
3.31
3.20
3.32 d
JK-7-1
6.88
5.46
5.02
5.79 a
JK-18-4
6.67
5.52
5.34
5.84 a
JK 23-1
5.30
5.00
4.84
5.05 abc
JOG 11-10
5.63
5.42
5.31
5.46 ab
MBE-SP
5.82
4.47
4.25
4.85 bc
NSIC 23
5.93
5.07
3.57
4.86 bc
NSIC 31
5.41
4.54
4.37
4.77 bc
TAIWAN – D
3.92
5.04
4.08
4.34c
Inubi-CA 5.58
4.98
4.65
5.07 abc
L- Mean
5.46a
4.88b
4.46c
4.93
CV(%)= 16.1
*Means with the same letters are not significantly different at 5% level by DMRT
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Growth Parameters
Plant
Vigor
Effect of genotype. There were remarkable differences on plant vigor
among the different genotypes at 30 DAP (Table 23). Genotypes JOG 11-10,
NSIC 23, NSIC 31, Unubi-CA, Taiwan D, JK 7-4 and MBE- SP exhibited
highly vigorous growth. Genotypes JK 18- 4 and BSU # 1 had moderate vigor
rates.
Level of water stress effect. Plant vigor at 30 DAP was not significantly
affected by level of water stress (Table 23), although the highest plant vigor rating
was observed from genotypes under moderate stress condition (60 cb) with 4.77
(highly vigorous).
Interaction effect. Genotypes and level of water stress did not
significantly affect plant vigor at 30 DAP. Genotypes JK 7-1, JOG 11-10, NSIC
31, Taiwan D and Inubi –CA under any level of water stress had highly
vigorous growth. The least plant vigor was observed from genotype BSU # 1
under severe stress. Plant vigor is affected primarily by inherent characteristic;
secondary is the environment where the crop is grown (OSU, 1997).
Screening And Evaluation Of Sweet potato Genotypes
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Table 23. Plant vigor of the 10 sweetpotato genotypes as affected level of
water stress
PLANT
VIGOR
*
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
3.67
4.00
3.33
3.67 c
JK-7-1
5.00
5.00
5.00
5.00 a
JK-18-4
4.33
4.33
4.33
4.33 b
JK 23-1
4.67
4.67
4.67
4.67 ab
JOG 11-10
5.00
5.00
5.00
5.00 a
MBE-SP
4.67
4.67
5.00
4.78 a
NSIC 23
5.00
5.00
5.00
5.00 a
NSIC 31
5.00
5.00
5.00
5.00 a
TAIWAN- D
5.00
5.00
5.00
5.00 a
Inubi –CA
5.00
5.00
5.00
5.00 a
L-Mean 4.73a
4.77a
4.73a
4.73
Plant Vigor Rating: 5= Highly vigorous; 4= Moderately stress; 3= Vigorous; 2 =
Less vigorous; 1 = Poor vigor.
CV(%)=7.8
*Means with the same letters are not significantly different at 5% level by DMRT.
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Vine length at 35 DAP
Effect of genotype. Vine length significantly varied at 35 DAP among the
different genotypes (Table 24). Genotype JK 7- 4 exhibited the longest vines
but not significantly different with genotypes JK 23-1, NSIC 23, BSU # 1, and
Inubi- CA. The shortest vines were observed from JK 18-4.
Effect of water level of stress. Vine length at 35 days was not
significantly affected by the level of water stress ( Table 24). Although it can be
seen that genotypes under severe stress condition (80 cb) had the longest vines
followed by genotypes under moderate stress (60 cb) while genotypes under
control condition (20 cb) the shortest vines. Varied vine lengths could be due to
the soil moisture used for cell elongation.
Interaction
effect. The interaction of genotypes and level of water stress
did not significantly affect the vine length 35 DAP. Genotype JK 7-4 under
severe stress condition (80 cb) was noted to have the longest vines. Vine growth
could be due to the genotypic characteristic affected by environment. In the case
of JK producing long vines, the condition is possible. Other treatment
combinations had lengths ranging from 59.33 cm to 149.07 cm.
Screening And Evaluation Of Sweet potato Genotypes
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Table 24. Vine length at 35 DAP of the 10 sweetpotato genotypes as affected
by level of water stress
VINE LENGTH (cm)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
131.47
157.27
135.27
138.00 a
JK- 7-1
135.07
127.27
180.73
147.69 a
JK-18-4 70.73
59.33
58.40
62.82 c
JK 23-1
138.60
154.93
147.07
146.87 a
JOG 11-10
113.73
128.00
134.20
125.31 a
MBE-SP
118.40
136.53
134.60
129.84 a
NSIC 23
129.60
137.80
149.07 138.82
a
NSIC 31
95.27
95.93
107.07
99.42 b
TAIWAN D
66.47
81.67 73.40
73.84
c
Inubi–CA
122.40
136.67 138.67
132.58 a
L-Mean
112.17 a 120.54
a 125.85
a 119.52
CV(%) =19.7
*Means with the same letters are not significantly different at 5% level by DMRT.
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Vine length at 70 and 105 DAP
Effect of genotype. Genotypes significantly varied in their vine length at
70 DAP (Table 25). Genotype BSU # 1 exhibited the longest vines at 70 DAP
followed by Inubi–CA. Genotypes JK 7-4, MBE –SP, JK 23-1 and JOG 11-10
had comparable vine lengths with BSU #1 and Inubi –CA. The shortest vines
were observed from genotype JK 18-4. It also observed that all genotypes
under different level of water stress had increased in vine length from 35 to 70
DAP. Vine length is primarily a genotypic characteristic (OSU, 1997), however,
different genotypes have different sensitivity to the environment. For instance
Taiwan D and JK 18-4 produce short vines to conserve water, thus coping with
water stress. Other genotypes like BSU #1 and Inubi-CA produce long vines also
a coping mechanism by more roots per node as the vine creeps on the ground.
At 105 DAP genotype Inubi- CA registered the longest vines but not
significantly different with BSU #1. Genotypes MBE-SP, JOG 11-10, JK23-1
and JK 7-4 had comparable vine lengths with Inubi - CA and BSU # 1.
The adaptive mechanism of sweetpotato to drought condition include vine
length. The vines elongate with increasing moisture stress. According to Hammett
et al. (1982), sweetpotatoes are considered moderately tolerant to drought
conditions due to their low plant growth habit and extensive root system. This is
supported by the data in Table 33 where root elongates with increasing moisture
stress.
Screening And Evaluation Of Sweet potato Genotypes
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Effect of water level of stress. Vine length at 70 DAP was significantly
affected by level of water stress (Table 25). Genotypes under severe stress
condition (60 cb) had the longest vines followed by genotypes under moderate
stress condition (60 cb), and the lowest vine length was observed from genotypes
under control condition (20 cb) .
Vine length at 105 DAP was significantly affected by level of water stress
(Table 26). Genotypes under moderate stress (60 cb) had the longest vines
followed by genotypes under severe stress condition (60 cb) and the lowest vine
length was observed from genotypes under control condition (20 cb).
Interaction
effect. The interaction of genotypes and level of water stress
did not significantly affect the vine length of the plant at 70 and 105 DAP.
Genotype Inubi –CA under severe stress condition (60 cb) produced the longest
vines while the shortest vines were observed from genotype Taiwan D under
severe stress (80 cb). Other treatment combinations had vine length ranging from
151.15 cm to 338.13 cm.
Screening And Evaluation Of Sweet potato Genotypes
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Table 25. Vine length (cm) at 70 DAP of 10 selected sweetpotato genotypes as
affected by level of water stress
VINE LENGTH (cm)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
271.37
248.52
262.60
260.83 a
JK- 7-1
231.76
255.26
264.38
250.47 ab
JK-18-4
151.15
166.07
170.71
162.64 d
JK 23-1
213.12
231.55
249.72
231.40 abc
JOG 11-10
210.74
229.46
246.38
228.86 abc
MBE-SP
218.42
249.93
272.29
246.88 abc
NSIC 23
188.48
204.03
243.02
211.84 bc
NSIC 31
205.96
195.98
228.75
210.23 c
TAIWAN- D
145.42
175.82
186.29
169.18 d
Inubi -CA
219.90
274.10
285.60
259.86 a
L-Mean
205.63c 223.05
b
240.97 a
CV(%)= 16.5
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
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Table 26. Vine length (cm) at 105 DAP of the10 selected sweetpotato genotypes
as affected by level of water stress
VINE LENGTH (cm)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
385.87
442.40
345.47
391.24 a
JK- 7-1
307.00
322.40
338.13
322.51 ab
JK-18-4
216.27
462.80
203.40
294.16 b
JK 23-1
285.80
286.93
335.47
302.73 ab
JOG 11-10
279.33
305.00
333.20
305.84 ab
MBE-SP
296.40
340.60
287.47
308.16 ab
NSIC 23
257.47
303.67
300.60
287.24 b
NSIC 31
262.80
262.93
278.80
268.18 bc
TAIWAN- D
214.93
229.93
150.20
198.36 c
Inubi-CA
360.20
462.80
352.40
391.80 a
L-Mean
286.61 b 341.95
a 292.51
b
CV(%) = 16.5
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
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Number of Vine Cuttings per plant
Effect of genotype. Number of vine per plant was significantly
different among the genotypes (Table 27). Genotype BSU # 1 had the most
vines while the lowest vine number was observed from genotype Taiwan D.
Table 27. Vine number cutting per plant of the 10 selected sweetpotato
genotypes as affected by level of water stress
NUMBER OF VINES
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
7.71 a
8.84 a
4.91 a
7.82 a
JK- 7-1
6.14 a
6.44 a 6.76
a
6.45 ab
JK-18-4 4.32
a 9.25
a 4.06
a
5.88 b
JK 23-1
5.72 a
5.73 a
6.72 a
6.06 ab
JOG 11-10
5.58 a
6.10 a
6.66 a
6.11 ab
MBE-SP 5.87
a
6.80 a 5.75
a
6.14 ab
NSIC 23
5.15 a
6.07 a
6.01 a 5.74
b
NSIC 31
5.26 a
5.26 a
5.57 a
5.36 bc
TAIWAN- D
4.30 a
4.59 a
3.00 a
3.96 c
Inubi –CA
7.20 a
9.25 a
7.07 a
7.83 a
L- Mean
5.72 b
6.83 a 5.86
b 6.14
CV(%) = 4.14
*Means with the same letters are not significantly different at 5% level by DMRT.
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Effect of water stress level. The number of vine cuttings was significantly
affected by level of water stress. Genotypes under moderate stress condition
produced more number of vines than genotypes under normal.
Interaction
effect. Number of vine cuttings of plants as affected by the
genotypes and level of water stress was not significant. Although it can be seen
that genotypes JK 7-1 and Inubi–CA under moderate stress produced more
number of vine cuttings while the lowest number of vine cuttings was observed
from genotypes Taiwan D under severe stress condition.
Vine Weight per Plant
Effect of genotype. Vine weight was significantly different among the
genotypes (Table 28). The highest vine yield was observed from genotype NSIC
31 followed by Inubi-CA. Lowest vine yield was observed from JK -18-4.
Effect of level of water stress. Vine weight was significantly affected by
level of water stress (Table 28). Genotypes under moderate stress registered the
heaviest vine compared to genotypes under normal condition and genotypes
under severe stress condition.
Interaction
effect. Vine yield of plant as affected by genotypes and level
of water stress was significant (Figure 19). Genotype NSIC 31 produced the
heaviest vines under any level of water stress while the lowest was observed
from genotype JK 18-4. Other treatment combinations had vine weights ranging
from 376.33 to 845.00 g.
Screening And Evaluation Of Sweet potato Genotypes
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Table 28. Weight of vine per plant of the 10 selected sweetpotato genotypes as
affected by level of water stress
VINE WEIGHT (g)
LEVEL OF WATER STRESS
GENOTYPE CONTROL MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
484.67 de
592.00d 433.65e 503.44d
JK- 7-1
499.00 d
582.33d 441.33e 507.56d
JK-18-4 376.33
f
447.33e
266.00g
363.22f
JK 23-1
501.33 d
81.33 d
425.33 e
502.67 d
JOG 11-10
547.67 c
716.33c
458.67 de
574.22cd
MBE-SP 457.67
e
571.67d
361.00f 463.44
e
NSIC 23
473.00 de
560.67 d 508.67c 514.11d
NSIC 31
845.00a 928.33a 755.00a 842.78
a
TAIWAN- D
580.33c
727.67c
485.33cd 597.78c
Inubi –CA
691.00b
774.00b
678.33b 714.44b
L- Mean
545.60b
648.17 a 481.33
c
558.37
CV(%) = 4.0
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
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106
Figure 19. Vine weight of sweetpotato genotypes as affected by water stress level
Leaf area
Effect of genotype. Significant differences were noted on the area per
leaf of the different genotypes at 35, 50 and 65 DAP (Table 29, 30 and 31). All
genotypes had an increase area per leaf from 35 to 65 DAP.
Genotype BSU# 1 was noted to have the highest leaf area at 35 DAP.
Genotypes NSIC 23, Taiwan D, JK 23-1, JOG 11-10 and Inubi-CA had
comparable leaf area with BSU #1. The lowest leaf area was observed from
genotypes MBE-SP.
Genotypes BSU # 1 registered the highest leaf area but not significantly
different with Inubi – CA. Genotypes JK 7-4, JK 23-1, MBE-SP and JOG -11-10
Screening And Evaluation Of Sweet potato Genotypes
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107
were comparable with BSU #1 and Inubi- CA. The lowest leaf area was
observed from genotypes Taiwan D.
At 65 DAP genotype Inubi- CA had a mean of 310.56 while the lowest
leaf area was observed from JK 18-4.
Level of water stress effect. Area per leaf at 35 DAP was not greatly
affected by level of water stress. Area per leaf of genotypes under moderate
stress (60 cb) registered the highest followed by genotypes under control
condition (20 cb) while the lowest leaf area was observed from genotypes under
severe stress condition (80 cb). The results conforms with the study of
Mickelbart (2010) that the leaf characteristic of drought tolerant plants are
characterized as having small leaves, with leaf waxes, and minimal leaf area all
lead to reduced water loss, and therefore, drought tolerance. Tongket et al. (1991)
also found that the response of water stress in earlier stage in sweetpotato
inhibited the leaf growth than the root growth. Water stress caused a reduction of
leaf size in Centennial variety and in leaf number in other genotypes of
sweetpotato.
Level of water stress significantly affected the area per leaf at 50 and 65
DAP (Table 28 and 29). Leaf area of all genotypes under different levels of water
stress increased. Genotypes under moderate (60 cb) registered the highest leaf
area followed by genotypes under control condition (20 cb) while the lowest
leaf area was observed from genotypes under severe stress condition (80 cb).
Screening And Evaluation Of Sweet potato Genotypes
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108
Table 29. Leaf area (cm2) at 35 DAP of the 10 sweetpotato selected genotypes
as affected by level of water stress
LEAF AREA (cm2)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
101.70
87.51
88.76
92.66 a
JK- 7-4
42.85
64.98
55.98
54.60 c
JK-18-4
57.98
58.71
65.57
61.09 bc
JK 23-1
85.80
68.54
77.27 77.20
ab
JOG 11-10
79.83
76.54
63.11
73.16 abc
MBE-SP
64.18
55.81
42.33
54.11 c
NSIC 23
76.13
89.58
86.42 84.04
ab
NSIC 31
70.28
68.85
60.80
66.64 bc
TAIWAN- D
88.02
80.23
83.04
83.76 ab
Inubi –CA
76.70
71.48
67.25
71.81 abc
L-Mean
74.35 a 72.22
a 69.15
a 71.91
CV(%) =5.55
*Means with the same letters are not significantly different at 5% level by DMRT.
Water deficit or insufficient water supply inhibits cell division and expansion
resulting in the production of smaller leaves (Zaag, 1992; ICPRE and UI-CALS,
2002; Pritchard and Amthor, 2005).
Screening And Evaluation Of Sweet potato Genotypes
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Table 30. Leaf area (cm2) at 50 DAP of the 10 selected sweetpotato genotypes
as affected by level of water stress
LEAF AREA (cm2)
LEVEL OF WATER STRESS
GENOTYPE
CONTROL MODERATE
SEVERE G- MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
259.40 a 242.47 a 296.00
a 265.96 a
JK- 7-1
218.33 ab 258.60
a 220.73
ab 232.56
ab
JK-18-4 142.40
b 130.67
bc 154.00
b 142.36
cd
JK 23-1
219.87 ab 207.53
ab 234.13
ab 220.51
ab
JOG 11-10
201.07 ab 233.20
a 27.07
ab 217.11
ab
MBE-SP 203.00
ab 210.60
ab 238.13
ab 217.24
ab
NSIC 23
176.80 ab 220.27
ab 187.07
b 194.71
b
NSIC 31
194.80 ab 190.27
abc 170.93
b 185.33
bc
TAIWAN- D
135.20 b 106.13
c 161.60
b 134.31
d
Inubi-CA 237.47
a 243.27
a 282.73
a 254.49
a
L-Mean
198.83
204.30
216.24
CV (%) =5.67
*Means with the same letters are not significantly different at 5% level by
DMRT.
Interaction
effect. Area per leaf of genotypes at 35 and 65 DAP was not
remarkably affected by the interaction of genotypes and level of water stress
(Table 27 and 29). Although the highest leaf area was observed from genotype
Screening And Evaluation Of Sweet potato Genotypes
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Table 31. Leaf area (cm2) at 65 DAP of the 10 selected sweetpotato genotypes as
affected by level of water stress
LEAF AREA (cm2)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
290.25
257.29
221.21
256.25 cd
JK- 7-1
304.39
274.48
245.31
274.73 bc
JK-18-4
270.96
233.26
203.11
235.78 d
JK 23-1
315.08
250.11
229.77
264.99 c
JOG 11-10
300.04
250.90
233.78
261.58 c
MBE-SP
289.86
257.49
240.89
262.75 c
NSIC 23
267.04
251.81
237.26
252.03 cd
NSIC 31
313.48
282.11
268.15
287.91 b
TAIWAN- D
265.70
234.52
210.16
236.79 d
Inubi-CA
352.69
309.49
269.48
310.56 a
L- Mean
296.95a 260.15b
235.91c
CV(%) = 8.0
*Means with the same letters are not significantly different at 5% level by DMRT.
BSU #1 under normal condition (20 cb) while the lowest leaf area was observed
from genotype MBE-SP under severe stress (80 cb). Other treatment combination
had the leaf area ranging from 42.85 to 89.58 cm2.
Screening And Evaluation Of Sweet potato Genotypes
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Leaf Area Index
Effect of genotype. Genotypes significantly differ in their leaf area index
(LAI) at 35, 50 and 65 DAP (Table 32,33 and 34). All genotypes used had an
increase LAI at 35, 50 up to 65 DAP having vigorous lateral shoots.
Table 32. Leaf area index at 35 DAP of the 10 selected sweetpotato genotypes
as affected by level of water stress
LEAF AREA INDEX
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
3.09
4.98
2.93
3.67 a
JK- 7-1
1.50
1.23
1.99
1.57 c
JK-18-4
1.51
1.56
1.27
1.44 c
JK 23-1
3.70
3.12
2.86
3.22 ab
JOG 11-10
2.48
2.92
2.02
2.47 bc
MBE-SP
1.22
1.98
1.59
1.60 c
NSIC 23
1.98
2.22
2.12
2.11 c
NSIC 31
2.17
1.80
1.99
1.99 c
TAIWAN- D
1.68
2.90
2.10
2.23 bc
Inubi-CA
1.89
2.53
1.59
2.00 c
L-Mean
2.12
2.52
2.05
CV(%) – 8.6
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
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Table 33. Leaf area index at 50 DAP of 10 selected sweetpotato genotypes as
affected by level of water stress
LEAF AREA INDEX
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
10.23 a
8.74 a
8.44 a
9.14 a
JK- 7-1
3.52 a
5.60 a
2.26 a
3.79 de
JK-18-4 3.93
a
4.90 a
3.19 a 4.00
d
JK 23-1
6.77 a
8.04 a
4.63 a
6.48 c
JOG 11-10
7.74 a
9.66 a
6.00 a
7.80 b
MBE-SP 2.63
a
3.48 a
1.87 a 2.66
e
NSIC 23
3.54 a
4.28 a
3.11 a
3.64 de
NSIC 31
5.82 a
6.30 a
4.63 a
5.58 c
TAIWAN- D
3.04 a
3.08 a
2.49 a
2.87 de
Inubi –CA
6.49 a
7.71 a
5.40 a
6.53 c
L-MEAN
5.37 b 6.18
a
4.20 c
CV(%) = 6.55
*Means with the same letters are not significantly different at 5% level by DMRT.
Results show significant differences among genotypes for LAI. Genotypes BSU#
1 exhibited the largest LAI but comparable with JK-23-1. The smallest LAI was
obtained from genotype JK-18-4 at 35 DAP. This could be due to shedding of
leaves and heavy infestation of cutworms.
Screening And Evaluation Of Sweet potato Genotypes
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Table 34. Leaf area index at 65 DAP of the 10 selected sweetpotato genotypes
as affected by level of water stress
LEAF AREA INDEX
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
14.39 a
13.19 a
15.92 a
14.50 a
JK- 7-4
12.61 a
8.40 a 13.73
a
11.58 abc
JK-18-4 5.98
a
9.80 b 8.29
a 8.02
bc
JK 23-1
10.88 a 13.58
a
15.30 a
13.25 ab
JOG 11-10
13.28 a
12.76 a
11.70 a
12.58 abc
MBE-SP 12.28 a
18.49 a
7.24 a 12.67
abc
NSIC 23
9.58 a 5.62
a 5.62
a 6.94
c
NSIC 31
15.28 a
8.86 a
12.27 a
12.14 abc
TAIWAN- D
4.18 a
10.92 a
4.95 a 6.69
c
Inubi -CA
9.97 a
23.38 a 12.92
a
15.43 a
L- Mean
10.98b
12.50a
10.80 c
CV(%) = 24.2
*Means with the same letters are not significantly different at 5% level by DMRT.
At 50 DAP, BSU#1 had the highest leaf area index while the lowest was
from MBE-SP and Taiwan-D at 50 and 65 DAP.
Level of water stress effect. LAI at 35 DAP was not significantly affected
by level of water stress although it is noted that plants under normal condition
Screening And Evaluation Of Sweet potato Genotypes
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(20 cb) registered the highest LAI. The lowest LAI was observed from
genotypes under severe stress condition (80 cb).
At 50 and 65 DAP, highest LAI was observed from moderate water stress..
This shows that sweetpotato can tolerate moderate stress condition, as shown by
normal leaf development. But at severe stress, leaf development is affected to an
extent that leaf development is reduced. This could be attributed to the defense
mechanism of having small leaves against water stress. As stated by
Akyeampong (1985), drought-stressed leaves were smaller than the unstressed
leaves in the case of cowpea.
Interaction effect. The interaction of genotypes and level of water stress
did not significantly affect the LAI of plants at 35 , 50 and 65 DAP. At 35 DAP,
Genotype BSU#1 under moderate stress condition exhibited the highest LAI
while the lowest LAI was observed from genotype JK-18-4 under severe stress
condition while MBE-SP had the lowest LAI at 50 DAP.
Root Weight at Harvest
Effect of genotype. There were significant differences on the root weight
at harvest of the different genotypes (Table 35). Genotype NSIC 31 produced the
heaviest root, while the lowest was observed from genotype JK 7-4. Other
genotypes had the root weight ranging from 4.92 to 12.61 g.
Level of water stress effect. Root weight at harvest was significantly
affected by level of water stress (Table 33). Genotypes under severe stress
Screening And Evaluation Of Sweet potato Genotypes
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Table 35. Root weight at harvest of the 10 selected sweetpotato genotypes as
affected by level of water stress
ROOT
WEIGHT
(g)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
5.54 e 3.54
g 5.68
g 4.92
f
JK- 7-1
5.04 f 2.63
h 6.86
f 4.84
f
JK-18-4 4.79
f 6.50
d
8.35 e 6.55
d
JK 23-1
4.77 f 5.24
f 6.53
f
5.52 e
JOG 11-10
5.81 de 5.73
e 8.81
d 6.79
d
MBE-SP 8.59
c 3.78
g 4.81
h 5.73
e
NSIC 23
4.77 f 6.74
d 6.55
f 6.01
e
NSIC 31
12.89 a 13.82
a 15.45
a 14.06
a
TAIWAN- D
6.17 d 8.67
c 9.34
c 8.06
c
Inubi -CA
10.88 b 12.52 b 14.45
b 12.61
b
L- Mean
6.92 b 6.92
b 8.68
a
CV(%) =3.0
*Mean with the same letters are not significantly different at 5% level of DMRT
condition (80 cb) registered the heaviest roots while the lowest was noted from
genotypes under control and moderate stress. This may be due to the mechanism
of the plants of having long roots during stress. Akyeampong (1985) and Hall
and Schulze (1980) found that in cowpea, increased root density and depth during
Screening And Evaluation Of Sweet potato Genotypes
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116
stress to exploit larger volume of soil to ensure the survival of the crop during
drought water stress and maintain plant status. Pritchard and Amthor (2005)
stressed that water stress sometimes stimulates root growth and this presumably
represents a mechanism to compensate for limited water supply. Moreover,
adaptation allow maximum growth and reproduction during dry period which
includes rapid development, C4 photosynthesis, high cuticular and stomatal
resistance to water loss, deep rooting systems, minimal leaf area, leaf rolling,
flagging and self shading.
Interaction effect. Genotypes and level of water stress interacted
significantly to affect root weight (Figure 20). Genotype NSIC 31 under severe
stress condition (60 cb) had the highest root weight while the lowest weight was
observed from genotype JK 23-1 under normal condition (20 cb).
Figure 20. Root weight as affected by the interaction of genotypes and level of
water stress
Screening And Evaluation Of Sweet potato Genotypes
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Root Length at harvest
Effect
genotype. There were significant differences on the root length of
the different genotypes (Table 36). Genotype JOG 11-10 exhibited the longest
roots while the shortest roots were obtained from NSIC 23.
Table 36. Root length at harvest of the 10 sweetpotato genotypes as affected by
level of water stress
ROOT
LENGTH
(cm)
LEVEL OF WATER STRESS
Genotype CONTROL
MODERATE
SEVERE
G-Mean
(20 cb)
(60 cb)
(80 cb)
BSU# 1
24.33 d 45.67
b 60.00
b 43.33 b
JK- 7-1
39.00 c 20.67
e 73.00
a 44.22
b
JK-18-4 35.33
c 44.33 b 57.67
b 45.78 b
JK 23-1
48.67 b 28.33
d 14.00
f 30.33
c
JOG 11-10
56.33 a 58.67
a 69.33
a 61.44
a
MBE-SP 53.00
a 55.00
a 21.00
e 43.00
b
NSIC 23
15.00 e 34.67
c 23.33
e 24.33
d
NSIC 31
37.00 c 14.33
f 30.33
d 27.22
d
TAIWAN- D
12.00 e 41.67
b 44.00
c 32.56
c
Inibi-CA 26.33
d 34.00
c 70.67
a 43.67
b
L-Mean
34.70 b 37.73
b 46.33
a
CV(%) = 6.1
*Means with same letters are not significantly different at 5% level by DMRT
Screening And Evaluation Of Sweet potato Genotypes
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Level of water stress effect. Length of roots at harvest was significantly
affected by level of water stress (Table 36). The longest roots were observed
from genotypes under severe stress condition (60 cb), followed by moderate
stress while the shortest roots were observed in genotypes under control
condition (20 cb).
Gurgel (2008) stated that indicators of drought tolerance is characterized
by having a deep root system and ability of leaf rolling since root play an
important role in controlling plant water status to avoid drought injury and leaves
roll under dry conditions, exposing less leaf surface to be in contact with dry air,
which was also observed during the study.
Fig. 15. Root length as affected by the interaction of genotypes and level of
water stress
Screening And Evaluation Of Sweet potato Genotypes
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119
Interaction effect. There was a significant interaction on the length of
roots as affected by genotypes and level of water stress (Figure 21). The longest
roots were observed from genotypes JK 7-4 under severe stress condition (60 cb)
while the shortest roots were observed from genotypes JK 23-1. Other treatment
combinations had root lengths ranging from 15.00 to 70.67 cm.
Incidence of Insect Pest and Diseases
Cutworm
Incidence
Effect
genotypes. Reaction to cutworm was significantly affected by
different genotypes (Table 37). Genotype JOG 11-10 had the lowest incidence
but not significantly different with genotypes JK 7-4, MBE-SP and BSU # 1. The
highest cutworm incidence was observed from JK 23-1.
Level of water stress effect. Incidence of cutworm was significantly
affected by level of water stress. Genotypes under severe stress condition (60 cb)
obtained the highest incidence rating of 2.73 followed by moderate stress
condition and the lowest rating was observed from genotypes under control
condition. It was observed that plants that were stressed are more susceptible to
cutworm infestation.
Interaction effect. Genotypes and level of water stress interacted significantly
with regards to incidence of cutworm (Figure 22). Genotype Inubi -CA under
severe stress incurred the highest incidence while the lowest rating was observed
Screening And Evaluation Of Sweet potato Genotypes
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Table 37. Cutworm incidence of the 10 selected sweetpotato genotypes as
affected by level of water stress
CUTWORM INCIDENCE *
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
1.00 b
2.00 bcd 2.33
cde 1.78
bc
JK- 7-1
1.00 b
1.67 cd 2.00
cde
1.56 bc
JK-18-4 1.00
b
1.00 d
4.00 ab 2.00b
JK 23-1
3.67 a
4.00 a
4.00 ab
3.89 a
JOG 11-10
1.00 b
1.67 cd
1.67 de
1.44 bc
MBE-SP 1.67
b
1.33 d
2.00 cde
1.67 bc
NSIC 23
3.33 a
3.33 ab
3.33 abc
3.33a
NSIC 31
3.33 a
2.33 bcd
1.00 e 2.22b
TAIWAN- D
1.67 b
2.33 bcd
2.67 bcd
2.22b
Inubi-CA 4.00
a
3.00 abc
4.33 a
3.78 a
L- Mean
2.17 b
2.27 b
2.73 a
2.39
* Rating scale: 1- no apparent injury; 2- injury confined to youngest leaf; 3- some
older leaves injured; 4-over 50% of the leaves injured; 5- over 90% of the leaves
injured
CV(%)- 10.56
*Means with the same letters are not significantly different at 5% level by
DMRT.
from genotypes JK 7 -4, JOG 11-10, BSU # 1 and JK 18-4 under control
condition.
Screening And Evaluation Of Sweet potato Genotypes
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Figure 22. Insect pest as affected by the interaction of genotypes and level of
water stress.
Leaf
Curling
Effect of genotype. The highest disease rating was observed from
genotype BSU#1 while genotypes JOG 11-10 and JK 18-7 had no disease
symptoms observed. JK 23-1 was susceptible to leaf curling while JOG 11-10
and JK 18-4 were highly resistant to leaf curling disease (Table 38).
Effect of water stress Level. Incidence of leaf curl disease was not
significantly affected by level of water stress ( Table 38). All genotypes under
different level of stress had ratings of 0.47 to 0.60, where there is 0 to 2.5 %
infection.
Screening And Evaluation Of Sweet potato Genotypes
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Table 38. Leaf curling incidence of 10 selected sweetpotato genotypes as
affected by level of water stress
LEAF CURLING INCIDENCE *
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
1.33
2.00
2.33
1.89 a
JK- 7-1
0.67
0.33
0.33
0.44 bc
JK-18-4
0.00
0.00
0.00
0.00 c
JK 23-1
1.00
1.67
1.67
1.44 a
JOG 11-10
0.00
0.00
0.00
0.00 c
MBE-SP
0.33
0.33
0.33
0.33 bc
NSIC 23
0.67
0.33
0.67
0.56 b
NSIC 31
0.00
0.33
0.00
0.11 bc
TAIWAN- D
0.67
0.67
0.33
0.56 bc
Inubi –CA
0.00
0.33
0.33
0.22 bc
L- Mean
0.47 0.60
0.60
*Disease rating: 0-no disease; 1- trace 5% infection; 2-5 -15% infection; 4- 35 to
65% infection; 5 – 67.5 to 100% infection.
CV(%)= 12.76
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
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123
Interaction
effect. The interaction of genotypes and level of water stress
did not significantly affect the incidence of viral disease. All genotypes under
different levels of water stress had ratings ranging from 0.00 to 2.33.
Correlation of Morphological, Physiological, Growth, Incidence of Insect pest
and Diseases and Vine yield Characters
The correlation coefficient between the vine yield at vine length (35, 70
and 105 DAP), leaf size (35, 50, and 65 DAP) leaf area index (35, 50 and 65 DAP)
of the different physiological, growth, morphological, incidence of pest and
diseases to vine yield are presented in Table 39.
Results revealed that drought score has negative significant correlation
with vine yield. This implies that genotypes lesser drought score produce more
vine yield. This collaborates with the findings of Ndler and Heuer (1995) that
there is a direct correlation between increasing drought and reduction in yield.
Drought causes wilting where cells become flaccid and leaves do not carry
assimilation normally (Dar,1980).
Root weight has positive significant correlation with vine yield. This
shows that genotypes with heavier roots have higher vine yield.
Screening And Evaluation Of Sweet potato Genotypes
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124
Table 39. Correlation coefficients of morphology, physiological, growth, insect
pest incidence, disease incidence to the vine yield.
COEFFICIENT OF
Characters
PROBABILITY
CORRELATION
No. of stomates in Abaxial
-.119ns .743
No. of stomates Adaxial
-.098ns .787
Drought score
-.688*
.028
Recovery rating
+471 ns .170
Disease incidence
.229ns .525
Insect Pest incidence
.+229 ns .524
Plant Vigor
+464 ns
.176
Root weight
+.883**
.001
Root length
-.279 ns .436
Leaf area index 65 DAP
+.289 ns .418
Leaf area index 50 DAP
+.217 ns .548
Leaf area index 35 DAP
+.019 ns .958
Leaf area 65 DAP
+.699*
.028
Leaf area 50 DAP
+.106 ns .772
Leaf area 35 DAP
+.166 ns .749
Vine Length at 35 DAP
+.007ns .985
Vine Length at 70 DAP
+.146ns .688
Vine Length 105 DAP
-.057ns .876
** = significant at 1% level
ns = not significant
* = significant at 5% level
Screening And Evaluation Of Sweet potato Genotypes
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125
Leaf area was significantly correlated with vine yield. This implies that
maintaining large leaves may help in increasing the vine yield of different
sweetpotato genotypes. This coincides with the view of Steppler (1967) that
among the contributory factor to high yield is the early establishment of large leaf
area.
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SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
Summary
The study was composed of two experiments, first was screening of
sweetpotato genotypes using uni-green techniques under room temperature and
the second was evaluation of selected genotypes for drought resistance under
greenhouse condition. The study aimed to screen sweetpotato genotypes from
various germplasm sources for drought resistance; determine the effect of water
stress on the growth of genotypes; evaluate the growth and yield of selected
sweetpotato genotypes for drought resistance under greenhouse condition;
determine the interaction effect of sweetpotato genotypes and levels of water
stress and to correlate growth parameters with vine yield of the sweetpotato
genotypes.
Genotype
Forty sweetpotato genotypes were evaluated for drought resistance using
uni-green technique. All the parameters used in evaluating the characters of the
genotypes were significantly different.
Genotypes JK 18-4 and UPL-SP 4 had the most number of stomates/cm2
on the abaxial and adaxial portions of leaves. Out of the 40 genotypes 38 had
planophyle leaf orientation while two genotypes (Japanese inubi and JK 23-1) had
erectophyle leaf orientation. All genotypes’ responses to water deficit were
Screening And Evaluation Of Sweet potato Genotypes
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127
shedding, rolling and dropping. NSIC 28 had the biggest leaf size and produced
the shortest roots.
Genotype MBE-SP produced more number of roots while Genotype JK
23-1 produced the longest roots, highest recovery rating and lowest drought
score resulting in the highest RWC. The highest increment in shoot growth was
observed from genotype NSIC 24 and the lowest increment was observed from
UPL-SP 3. The tallest plants were observed from genotype JK 18-4
Out of forty sweetpotato genotypes ten genotypes selected based on the
highest recovery rating, lowest drought score. long roots, more number of roots
and small leaves.
Genotype JOG 11-10 had the most number of stomates-1cm2 on the
abaxial and adaxial portions of leaves. Out of 10 genotypes 9 were noted that had
planophyle leaf orientation and only genotype JK 23-1 had erectophyle leaf
orientation.
Genotype Inubi –CA had the lowest drought score, high recovery rating,
tallest plants at 70 and 105 DAP, biggest leaf area at 65 DAP and lowest relative
water content at 35DAP.
Taiwan D registered the highest recovery rating, high plant vigor, smallest
plant at 70 and 105 DAP (169.86cm and 198.63 and lowest vine yield. Genotype
JK 7-4 registered the tallest plants at 35 DAP.
Screening And Evaluation Of Sweet potato Genotypes
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128
JK 18-4 was noted to have the smallest plants at 35 DAP, lowest leaf area
at 50 and 65 DAP, smallest leaf area index and lowest disease rating. BSU # 1
registered the biggest leaf area at 35, 50 and 65 DAP, highest leaf area index
and highest vine yield. JK 23 -1 noted the highest relative water content but not
significantly different with the other genotypes and NSIC 23 produced the
shortest roots but heaviest root. Genotype JOG 11-10 produced the longest root
lowest insect infestation.
Five genotypes had characters that can be considered as adaptive
mechanism for water stress such as; small to medium leaf area, high leaf area
index, long roots, more roots, long vines, more of vines and high vine yield.
Genotypes JOG 11-10, Inubi-Ca, Taiwan D, NSIC 23 and JK 18-4 exhibited
these characters. .
Water Stress
Genotypes under not stressed (20 cb) registered the lowest drought score,
highest recovery rating; lowest relative water content; highly vigorous plants,
lowest vine length at 35 and 105 DAP; highest leaf area; lowest root weight;
lowest root length; moderate resistance to cutworm; and few vine cuttings.
Genotypes under moderate stress (60 cb) produced had moderate drought
score and recovery rating; lowest relative water content; highly vigorous; tallest
plants and biggest leaf area index.
Screening And Evaluation Of Sweet potato Genotypes
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129
Plants under severe water stress had the highest drought score; lowest
recovery rating; highest relative water content; lowest plant vigor rating; tallest
plants; smallest leaf area; smallest leaf area index; heaviest roots and the longest
roots.
Interaction of Genotype and Water Stress Level
Genotype JOG 11-10 under moderate stress had the highest stomata-1cm2
on the abaxial and adaxial portions of the leaves and genotype JK 18-4 under
control condition produced the least stomata-1cm2 on the abaxial and adaxial
portions of the leaves; JK 18-4 and JK 7-1 under severe stress were the highest
drought score and the lowest was Inubi-CA under moderate stress.
Taiwan D under severe stress produced the highest recovery rating and
lowest were JK 18-4 and BSU # 1 under severe stress and JK 23-1 under severe
stress produced the highest relative water content and the lowest Inubi –CA
under normal and moderate stress; lowest plant vigor was observed from
genotype BSU #1 under severe stress condition.
Correlation of Characters
Vine yield was positively correlated to leaf size at 65 DAP and root
weight. Drought score had negative significant correlated to vine yield.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
130
Conclusions
Based on the results, the following conclusions are drawn:
1. Moderate water stress had negative effects on the morphological,
physiological and growth performance of the forty genotypes evaluated.
2. Plantlets under moderates stress produced smallest leaf area and leaf area
index, lowest drought score, high relative water content and smallest height
increment.
3. Ten best genotypes were selected such as NSIC 23,. NSIC 31, Taiwan D, JOG
11-10, JK 7-4, JK 18-4, JK 23-1, BSU #1 , MBE –SP and Inubi –CA which
exhibited drought resistant characteristics such as dropping and shedding of
leaves lower drought score, higher recovery rating, high RWC, medium to
small leaf area, and leaf area index and vigorous plants.
4. Plants under moderates stress and severe stress produced smallest leaf area
and leaf area index, heaviest roots, longest roots and highest RWC.
5. Production of sweetpotato can be still be feasible in soil with 60 cb soil
moisture matric potential .
6. Genotypes JOG 11-10, JK 18 -4, JK 7-4, Taiwan D, NSIC 31 and Inubi –CA
had drought resistant characteristic such as small leaf area and area index,
longest roots, low drought score , high recovery rating and more vine yield.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
131
7. Significant positive correlation between leaf area at 65 DAP and root weight
with vine yield in 10 genotypes and negative significant correlation existed
in drought score to vine yield.
Recommendation
Considering the findings in study , the following are recommended:
1. Genotypes NSIC 23, NSIC 31, Taiwan D, JOG 11-10, JK 7-4, JK 18-4, JK
23-1, BSU #1 , MBE –SP and Inubi –CA can be planted under 60 cb soil
moisture matric potential.
2. When soil matric potential is 80 cb genotypes JOG 11-10, JK 18 -1, NSIC 23,
Taiwan D and Inubi –CA can be planted.
3. Characters significantly correlated with vine yield can be used as selection
indices for sweetpotato genotypes under water stress condition.
4. Further studies need to be undertaken during dry season for drought resistant
genotypes under field condition.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
132
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Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
135
APPENDICES
Appendix Study 1
APPENDIX TABLE 1. Analysis of variance for number of stomates on the
abaxial portion of leaf
SV DF
SS MS F
Treatment
79
85493.6
1082.2
518.42 **
Genotype ( G )
39
77978.9
1999.5
957.82 **
Treatment (T)
1
3744.6
3744.6
1793.82 **
VxT 39
3770.10
96.7
46.31
**
Error 160
334.0
2.1
TOTAL 239
85827.6
CV (%) = 1.7
** = significant at 1 % level
APPENDIX TABLE 2. Analysis of variance for number of stomates on the
adaxial portion of leaf
SV DF
SS MS F
Treatment
79
630.545
7.982
5.19 **
Genotype ( G )
39
595.614
15.272
9.93 **
Treatment (T)
1
14.915
14.915
9.69 **
VxT 39
20.016
0.1513
0.33ns
Error 160
246.195
1.539
TOTAL 239
876.740
CV(%) = 7.5
** = significant at 1 % level
ns
=
non
significant
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
136
Appendix Table 3. Analysis of variance for leaf area
SV DF
SS MS F
Treatment
79
137735
1743
178.36 **
Genotype ( G )
39
107488
2756
281.96 **
Treatment (T)
1
3018
3018
308.70 **
V x T
39
27229
698
71.43 **
Error 160
1564
10
TOTAL 239
139299
CV (%) = 7.8
** = significant at 1 % level
APPENDIX TABLE 4. Analysis of variance for root length
SV DF
SS MS F
Treatment
79
550.203
6.965
79.15 **
Genotype ( G )
39
432.091
11.079
125.92 **
Treatment (T)
1
102.534
102.534
1165.33 **
VxT
39
15.578
0.399
4.54 **
Error 160
14.078
0.088
TOTAL 239
564.281
CV (%) = 4.2
** = significant at 1 % level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
137
APPENDIX TABLE 5. Analysis of variance for number of roots
SV DF
SS MS F
Treatment
79
1218.40
15.42
14.69 **
Genotype ( G )
39
1087.90
27.89
26.57 **
Treatment (T)
1
14.50
14.50
13.81 **
VxT 39
116.00
2.97
2.83
**
Error 160
168.00
1.05
TOTAL 239
1386.40
CV (%) = 12.6
** = significant at 1 % level
APPENDIX TABLE 6. Analysis of variance for vine length before exposing to
drought
SV DF
SS MS
F
Treatment
79
2105.90
26.66
940.38 **
Genotype ( G )
39
1622.16
41.59
1467.30 **
Treatment (T)
1
14.73
14.73
519.50 **
VxT
39
469.01
12.03
424.24 **
Error
160
4.54
0.03
TOTAL 239
2110.43
CV (%) = 1.2
** = significant at 1% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
138
APPENDIX TABLE 7. Analysis of variance for vine length after drought
imposition
SV DF
SS MS
F
Treatment
79
2224.66
28.16
242.69 **
Genotype ( G )
39
1839.49
47.17
406.49 **
Treatment (T)
1
142.96
142.96
1232.04 **
VxT
39
242.21
6.21
53.52 **
Error 160
18.57
0.12
TOTAL 239
CV (%) = 2.1
** = significant at 1% level
APPENDIX TABLE 8. Analysis of variance for drought score
SV DF
SS MS F
Treatment
79
830.053
10.507
100.73 **
Genotype ( G )
39
254.702
6.531
62.61 **
Treatment (T)
1
320.351
320.351
3071.23 **
VxT
39
255.000
6.538
62.68 **
Error 160
16.689
0.104
TOTAL 239
846.742
CV (%) = 15.0
** = significant at 1% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
139
APPENDIX TABLE 9. Analysis of variance for recovery rating
SV DF
SS MS F
Treatment
79
294.782
3.731
226.94 **
Genotype ( G )
39
143.050
3.668
223.08 **
Treatment (T)
1
8.645
8.645
525.77 **
VxT 39
143.087
3.669
223.14
**
Error
160
2.631
0.016
TOTAL 239
297.413
CV (%) = 1.5
** = significant at 1% level
APPENDIX TABLE 10. Analysis of variance for relative water content
SV DF
SS MS F
Treatment
79 10286.10 130.2 18.83**
Genotype ( G )
39
8670.2
222.3
32.16 **
Treatment (T)
1
437.9
437.9
63.34 **
VxT
39
1178.0
30.2
4.37 **
Error 160
1106.10
6.9
TOTAL 239
11392.2
CV (%) = 9.6
** = significant at 1 % level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
140
APPENDIX TABLE 11. Analysis of variance for percentage of survival
SV DF
SS MS F
Treatment
79
2967.30
37.56
1452.68 **
Genotype ( G )
39
2501.70
64.15
2480.88 **
Treatment (T)
1
134.58
134.58
5204.94 **
VxT 39
331.02
8.49
328.27**
Error 160
4.14
0.03
TOTAL 239
2971.44
CV(%) = 0.2
** = significant at 1 % level
APPENDIX TABLE 12. Analysis of variance for vine length at 10 DAP
SV DF
SS MS F
Treatment
79
515.501
6.525
10.58 **
Genotype ( G )
39
400.938
10.280
16.67 **
Treatment (T)
1
2.933
2.933
4.75 *
VxT
39
111.630
2.862
4.64 **
Error
160
98.694
0.617
TOTAL 239
614.195
CV(%) =11.7
** = significant at 1 % level
* = significant at 5% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
141
APPENDIX TABLE 13. Analysis of variance for vine length at 20 DAP
SV DF
SS MS F
Treatment
79
1908.03
24.15
122.73 **
Genotype ( G )
39
1498.08
38.41
195.19 **
Treatment (T)
1
8.66
8.66
43.99 **
VxT
39
401.29
10.29
52.28 **
Error 160
31.49
0.20
TOTAL 239
1939.52
CV (%) = 3.5
** = significant at 1% level
APPENDIX TABLE 14. Analysis of variance for vine length at 30 DAP
SV DF
SS MS
F
Treatment
79
1734.47
21.96
87.54 **
Genotype ( G )
39
1512.52
38.78
154.64 **
Treatment (T)
1
2.98
2.98
11.89 **
VxT
39
218.97
5.61
22.39 **
Error
160
40.13
0.25
TOTAL 239
1774.60
CV (%) = 3.5
** = significant at 1% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
142
APPENDIX TABLE 15. Analysis of variance for vine length for 40 at DAP
SV DF
SS MS
F
Treatment
79
3058.46
38.71
92.20 **
Genotype ( G )
39
2091.60
53.63
127.72 **
Treatment (T)
1
593.71
593.71
1413.95 **
VxT 39
373.15
9.57
22.79
**
Error 160
67.18
0.42
TOTAL 239
3125.65
CV (%) = 3.7
** = significant at 1% level
APPENDIX TABLE 16. Analysis of variance for vine length for 50 at DAP
SV DF
SS MS
F
Treatment
79
6288.15
79.60
144.42 **
Genotype ( G )
39
2923.37
74.96
136.00 **
Treatment (T)
1
2572.25
2572.25
4667.11 **
VxT 39
792.53
20.32
36.87
**
Error 160
160
88.18
0.55
TOTAL 239
6376.34
CV (%) = 3.6
** = significant at 1% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
143
Appendix Study 2
APPENDIX TABLE 17. Analysis of variance for number of stomates on the
abaxial portion of leaves
SV DF
SS MS
F
Replication ( R )
2
11.4
5.7
2.27*
Treatment 29
37372.6
1288.7
742.67**
Genotype (G)
9
15320.2
1702.2
980.98**
Factor (B)
2
14866.3
7433.10
4283.62**
GxT 18
7186.2
399.2
230.07**
Error 58
100.6
1.7
TOTAL 89
37484.6
CV (%)= 1.3
** = significant at 1 % level
*
=
significant
at
5
%
level
APPENDIX TABLE 18. Analysis of variance for number of stomates on the
adaxial portion of leaves
SV DF
SS MS
F
Replication ( R )
2
11.4
5.7
2.27*
Treatment 29
37372.6
1288.7
742.67**
Genotype (G)
9
15320.2
1702.2
980.98**
Factor (B)
2
14866.3
7433.10
4283.62**
GxT 18
7186.2
399.2
230.07**
Error 58
100.6
1.7
TOTAL 89
37484.6
CV (%) = 1.3
** = significant at 1 % level
* = significant at 5 % level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
144
APPENDIX TABLE 19. Analysis of variance for drought score
SV DF
SS MS
F
Replication ( R )
2
10.4569800
5.2284900
4.84 *
Treatment 29
449.8982100
15.5137314
14.36
**
Genotype (G)
9
89.3772989
9.9308110
9.19 **
Factor (B)
2
312.4756467
156.2378233
144.64 **
GxT 18
48.0452644
2.6691814
2.47
**
Error 59
61.5724200
1.0802179
TOTAL 89
521.9276100
CV (%) = 5.09
** = significant at 1 % level
* = significant level at 5% level
APPENDIX TABLE 20. Analysis of variance for recovery rating
SV DF
SS MS F
Replication ( R )
2
1.1555556
0.5777778
< 1
Treatment 29
306.4888889
10.5685824
12.38
**
Genotype (G)
9
55.8222222
6.2024691
7.27 **
Factor (B)
2
202.7555556
101.3777778
118.76 **
GxT 18
47.9111111
2.6617284
3.12
**
Error 58
49.5111111
0.8536398
TOTAL 89
357.1555556
CV (%) = 12.9
** = significant at 1% level
Screening And Evaluation Of Sweet potato Genotypes
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145
APPENDIX TABLE 21. Analysis of variance for relative water content
SV DF
SS MS F
Replication ( R )
2
192.818
96.409
39.51 **
Treatment 29
37.326
1.287
0.53
ns
Genotype (G)
9
23.631
2.626
1.08 ns
Factor (B)
2
10.293
5.147
2.11 ns
GxT 18
3.401
0.189
0.18
ns
Error 58
141.523
2.440
TOTAL 89
371.666
CV (%) = 5.38
** = significant at 1 % level
ns
=
not
significant
APPENDIX TABLE 22. Analysis of variance for net assimilation rate at 35 DAP
SV DF
SS MS
F
Replication ( R )
2
0.8501
0.4251
2.17 ns
Treatment 29
50.2446
1.7325
8.83**
Genotype (G)
9
25.7474
2.8608
14.58**
Factor (B)
2
21.0662
10.5331
53.68**
GxT
18
3.4310
0.1906
<1
Error 58
11.3798
0.1962
TOTAL
89
62.4745
CV (%)= 14.1
** = significant at 1 % level
ns
=
not
significant
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
146
APPENDIX TABLE 23. Analysis of variance for net assimilation rate at 50
DAP
SV DF
SS MS
F
Replication ( R )
2
2.881
1.441
1.94ns
Treatment 29
91.117
3.142
4.24
**
Genotype (G)
9
54.363
6.040
8.14**
Factor (B)
2
17.746
8.873
11.96**
GxT 18
19.008
1.056
1.42ns
Error 58
43.024
0.742
TOTAL
89
137.022
CV(%)=22.9
* = significant at 5 % level
APPENDIX TABLE 24. Analysis of variance for net assimilation rate at 65 DAP
SV
DF
SS
MS
F
Replication ( R )
2
0.2693756
0.1346878
< 1
Treatment 29
71.3263789
2.4595303
3.89
**
Genotype (G)
9
43.6063567
4.8451507
7.67 **
Factor (B)
2
15. 0386689
7.5193344
11.90 **
GxT
18
12.6813533
0.7045196
1.11 ns
Error 58
36.6622911
0.6321085
TOTAL 89
108.2580456
CV(%) = 16.1
** = significant at 1 % level
ns = not significant
Screening And Evaluation Of Sweet potato Genotypes
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147
APPENDIX TABLE 25. Analysis of variance for plant vigor
SV DF
SS MS
F
Replication ( R )
2
0.82222222
0.41111111
3.04 ns
Treatment 29
16.45555556
0.56743295
4.20
**
Genotype (G)
9
15.56666667
1.72962963
12.79 **
Factor (B)
2
0.02222222
0.01111111
< 1
GxT
18
0.86666667
0.04814815
< 1
Error 58
7.84444444
0.13524904
TOTAL 89
25.12222222
CV (%) = 7.8
** = significant at 1% level
ns
=
not
significant
APPENDIX TABLE 26. Analysis of variance for vine length at 35 DAP
SV DF
SS
MS
F
Replication ( R )
2
531
265
< 1
Treatment 29
83446
2877
5.18
**
Genotype (G)
9
74438
8271
14.88 **
Factor (B)
2
2851
1426
2.56 ns
GxT 18
6157
342
<
0
Error 58
32248
556
TOTAL 89
116226
CV (%) = 19.7
** = significant at 1% level
ns
=
not
significant
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
148
APPENDIX TABLE 27. Analysis of variance for vine length at 70 DAP
SV DF
SS MS
F
Replication ( R )
2
9436
4718
3.47 *
Treatment 29
127371
4392
3.23
**
Genotype (G)
9
99418
11046
8.13 **
Factor (B)
2
18735
9367
6.89 **
GxT 18
9219
512
<
1ns
Error 58
78801
1359
TOTAL 89
215608
CV (%) = 16.5
** = significant at 1% level
*
=
significant level at 5% level
APPENDIX TABLE 28. Analysis of variance for vine length at 105 DAP
SV DF
SS MS
F
Replication ( R )
2
46455
23228
2.98 ns
Treatment 29
451748
155578
2.00
*
Genotype (G)
9
255741
28416
3.64 **
Factor (B)
2
55411
27705
3.55 *
GxT
18
140597
7811
1.00 ns
Error 58
452524
7802
TOTAL 89
950728
CV (%) = 28.8
** = significant at 1 % level
* = significant level at 5% level
ns = not significant
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
149
APPENDIX TABLE 29. Analysis for variance for leaf area at 35 DAP
SV DF
SS MS
F
Replication ( R )
2
0.316
0.158
< 1
Treatment 29
57.081
1.968
1.41
ns
Genotype (G)
9
43. 076
4.786
3.44 **
Factor (B)
2
0.925
0.463
< 1
GxT
18
13. 080
0.727
< 1
Error 58
80.801
1.393
TOTAL 89
CV (%) = 5.55
** = significant at 1% level
ns = significant
APPENDIX TABLE 31. Analysis of variance leaf area at 65 DAP
SV DF
SS MS F
Replication ( R )
2
23824
11912
26.33 **
Treatment 29
103081
3555
7.86
**
Genotype (G)
9
41415
4602
10.17 **
Factor (B)
2
56677
28338
62.63 **
GxT 18
4989
277
<
1
Error 58
26243
452
0.612
TOTAL 89
153148
CV(%) = 8.0
** = significant at 1 % level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
150
APPENDIX TABLE 32. Analysis of variance for leaf area index at 35 DAP
SV DF
SS MS
F
Replication ( R )
2
0.0046
0.0023
0.06 ns
Treatment 29
1.8280
0.0630
1.71
*
Genotype (G)
9
1.3719
0.1524
4.14 **
Factor (B)
2
0.1089
0.0544
1.48 ns
GxT
18
0.3473
0.0193
0. 52 ns
Error 58
2.1369
0.0368
TOTAL 89
3.9694
CV (%) = 8.6
** = significant at 1 % level
*= significant at 5 % level
APPENDIX TABLE 33. Analysis of variance for leaf area index at 50 DAP
SV DF
SS MS
F
Replication ( R )
2
3.1377
1.5688
2.82 ns
Treatment 29
21.8757
0.7543
1.36
ns
Genotype (G)
9
12.3013
1.3668
2.46 *
Factor (B)
2
0.6636
0.3318
0.60 ns
GxT 18
8.9108
0.4950
0.89
ns
Error 58
32.2534
0.5561
TOTAL 89
57.2667
CV(%) = 6.55
** = significant at 1 % level
* = significant at 5 % level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
151
APPENDIX TABLE 35. Analysis of variance for root weight at harvest
SV DF
SS
MS F
Replication ( R )
2
1.04
0.52
10.41 **
Treatment 29
1015.04
35.00
701.50
**
Genotype (G)
9
845.00
93.89
1881.71 **
Factor (B)
2
62.29
31.15
624.24 **
GxT 18
107.75
5.99
119.98
**
Error 58
2.89
TOTAL 89
1018.98
CV (%) = 3.0
** = significant at 1% level
APPENDIX TABLE 36. Analysis of variance for root length
SV DF
SS MS
F
Replication ( R )
2
7.6
3.8
< 1
Treatment 29
27795.8
958.5
166.25
**
Genotype (G)
9
9904.7
1100.5
189.50 **
Factor (B)
2
2185.0
1092.5
189.50 **
GxT 18
15706.2
872.6
151.35
**
Error 58
334.4
5.8
TOTAL 89
28137.8
CV (%) = 6.1
** = significant at 1% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
152
APPENDIX TABLE 37. Analysis of variance for cutworm incidence
SV DF
SS MS
F
Replication ( R )
2
3.756
1.878
2.54 ns
Treatment 29
106.722
3.680
4.97
**
Genotype (G)
9
69. 833
7.759
10.49 **
Factor (B)
2
5.489
2.744
3.71 *
GxT 18
31.400
1.744
2.36
**
Error 58
42.911
0.740
TOTAL 89
153.389
CV (%) = 36.0
** = significant at 1 % level
* = significant level at 5% level
ns = not significant
APPENDIX TABLE 38. Analysis of variance for leaf curled incidence
SV DF
SS MS F
Replication ( R )
2
0.0403
0.0201
3.94 *
Treatment 29
0.8063
0.0278
5.44
**
Genotype (G)
9
0.7277
0.0809
15.82 **
Factor (B)
2
0.0075
0.0037
< 1
GxT 18
0.0712
0.0040
<
1
Error 58
0.2965
0.0051
TOTAL 89
1.1431
CV (%) = 12.76
** = significant at 1% level
* = significant level at 5% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
153
APPENDIX TABLE 39. Analysis of variance for number of vine cuttings
SV DF
SS MS
F
Replication ( R )
2
0.4170
0.2085
3.22 *
Treatment 29
3.9376
0.1358
2.10
**
Genotype (G)
9
2.2626
0.2514
3.89 **
Factor (B)
2
0.4458
0.2229
3.45 *
GxT 18
1.2292
0.0683
1.06
ns
Error 58
3.7508
0.0647
TOTAL 89
8.1054
CV(%) = 4.14
** = significant at 1 % level
* = significant at 5 % level
APPENDIX TABLE 39. Analysis of variance for vine weight
SV DF
SS MS
F
Replication ( R )
2
1805
903
1.83 ns
Treatment 29
1971091
67969
137.69**
Genotype (G)
9
1483249
164805
333.86 **
Factor (B)
2
424835
212417
430.31 **
GxT 18
63007
3500
7.09**
Error 58
28631
494
TOTAL 89
20011527
CV(%) = 4.0
** = significant at 1 % level
ns = not significant
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
154
BIOGRAPHICAL SKETCH
The author is the eldest of four daughter of Villamor Cacal and Rosita
Velasco, Nipaco, Paniqui, Tarlac. She was born on July 12, 1975 in Nipaco,
Paniqui, Tarlac.
She finished her elementary education in Nipaco, Elementary School,
Paniqui, Tarlac, She enrolled in Balaoang National High School and graduated
as fist honorable mention. She spent her college days at Tarlac College of
Agriculture and obtained a degree of Bachelor of Science in Agriculture major in
Agronomy and minor in Crop Protection. During her college life she was a
recipient of Eduardo Cojuangco Foundation and a scholar of Shouichi Yoshida
Memorial Foundation. She finished her Master in Agriculture major in
Agronomy minor in Farming ystem in 2006 at Tarlac College of Agriculture. In
order to gain more knowledge she pursued her Ph.D in Agronomy minor in Rural
Development at Benguet State University.
After obtaining her bachelor’s degree she worked with the Uni-green
Incorporated as Researcher of Ornamental Plants and Japanese vegetable at, Lipa,
Batangas. In November, 1999 to 2002 she was a Science Research Assistant at
Pangasinan State University in Sta Maria, Pangasinan because of her willingness
to share her expertise on tissue culture to her Alma mater she transferred at
Tarlac College of Agriculture and now she is a faculty of the Institute of
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
155
Agriculture and Forestry and In-charge of the Tissue Culture Laboratory Project
of the College.
In 2000, she got married to Ruben P. Perey of Mendez, Cavite and
blessed two children: Julie Hanna and Jan Benedict.
Agnes
Cacal
Perey
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
Uni-green Technique. . . . . . . . . . . . . . . . . .
29
Germplasm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
Establishment of Mother plants . . . . . . . . . . . . . . . . . . . . . . . . .
29
Experimental Design and treatments . . . . . . . . . . . . . . . . . . . . .
33
Preparation of Planting Materials . . . . . . . . . . . . . . . . . . . . . . . .
33
Preparation of Floral Foam and Single-node Planting Materials
34
Fertilizer Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
Drought Stress Imposition . . . . . . . . . . . . . . . . . . . . . . . . . . . .
35
Data Gathered . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . ..
36
Experiment ll. Evaluation of Selected Genotypes for Drought
Resistance under Greenhouse Condition . . .
39
Experimental Design and Treatments . . . . . . . . . . . . . . . . . . . .
40
Crop Establishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Drought Imposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Control of Insect Pest, Diseases . . . . . . . . . . . . . . . . . . . . . . . .
42
The Data Gathering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
42
Statistical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45
RESULTS AND DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
46
Experiment l. Screening of Sweetpotato Genotypes using
46
Uni-green Technique . . . . . . . . . . . . . . . . . . .
Morphological Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
46
Number of Stomates on the Abaxial Portion of Leaves
46
Number of Stomates on the Abaxial Portion of Leaves
48
Leaf Characters . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . .
50
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
Leaf Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
51
Roots Length. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
54
Number of Roots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
56
Length of Shoots Before and After Water Stress
Imposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
59
Physiological Parameters . . . . . . . . . . . . . . . . . . . . .. . . . . . . . .
63
Drought Score . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .
63
Recovery Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
65
Relative Water Content . . . . . . . . . . . . .. . . . . . . . . . . .
65
Other Growth Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
69
Percentage survival . . . . . . . . . . . . . . . .. . . . . . . . . . . . .
69
Plant Vigor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .
69
Plant Height every 10 days . . . . . . . . . . . . . . . . . . . . . .
71
Experiment ll. Evaluation of Selected Genotypes for drought
Resistance under Greenhouse Condition . . . . . . . . . . . . . .
76
Meteorological Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
76
Morphological Parameters . . . . . . . . . . . . . . . .. . . . . . . . . . . . .
77
Number of Stomates on the Abaxial Portion of Leaves
77
Number of Stomates on the Adaxial Portion of Leaves
80
Leaf Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
83
Physiological Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
83
Drought Score . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .
83
Recovery Rating . . . . . . . . . . . . . . . . . . . . . . . . . . .
86
Relative Water Content . . . . . . . . . . . . . . . . . . . . . . .
88
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
Net Assimilation Rate . . . . . . . . . . . . . . . . . . . . . . . .
90
Growth Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
95
Plant Vigor . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . .
95
Vine length at 35 DAP . . . . . . . . . . . . . . . . . . . . . . . . .
97
Vine length at 70 and 105 DAP . . . . . . . . . . . . . . . . . . .
99
Number of vine cuttings . . . . . . . . . . . . . . . . . . . . . . . .
103
Vine Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .
104
Leaf Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
106
Leaf Area Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
111
Root Weight a Harvest . . . . . . . . . . . . . . .. . . . . . . . . . .
114
Root Length at harvest . . . . . . . . . . . . . . . . . . . . . . . . .
117
Incidence of Insect Pest and Diseases . . . . . . . . . . . . . . . . . .
119
Cutworm Incidence . . . . . . . . . . . . . . . . . . . . . . . . . . .
119
Leaf curling Incidence . . . . . . . . . . . . . . . . . . . . . . . . .
121
Correlation of Morphological, Physiological, Growth,
Incidence of Pest and Diseases and Vine Yield. . . . . . . . . . . .
123
SUMMARY, CONCLUSIONS AND RECOMMENDATIONS. . . . . . 126
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
126
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .
130
Recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
131
LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
135
BIOGRAPHICAL SKETCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
154
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
AGNES C. PEREY, April 2012. Screening and evaluation of sweetpotato
genotypes for water stress resistance. Benguet State University, La Trinidad,
Benguet.
Adviser: Belinda A. Tad-awan, Ph.D.
ABSTRACT
The study aimed to screen sweetpotato genotypes from various germplasm
sources for drought resistance, determine the effect of water stress on the growth
ofthe genotypes, evaluate the growth and yield of selected sweetpotato genotypes
for drought resistance under greenhouse condition, and determine the interaction
effect of sweetpotato genotypes and levels of water stress.
Forty
sweetpotatogenotypeswith varying leaf and stem characters were
exposed to two (2) levels of water stress (no stress and moderate stress) under
room temperature (27 oC).
Results showed that among the genotypes evaluated, ten best genotypes
(NSIC 23, NSIC 31, Taiwan D, JOG 11-10, JK 7-4, JK 18-4, JK 23-1, BSU #1,
MBE–SP and Inubi – CA) were observed to have drought resistant characteristics
based on plant characters such as low dropping and shedding of leaves, lowest
drought score, high recovery rating,and relative water content, small leaf area per
plant, leaf area index, vigorous plants, more roots, longer shoot length increment
and longest roots.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
Ten selected sweetpotato genotypes were further evaluated for drought
resistance under greenhouse condition.
Results showed that genotype JOG 11-10 had the highest number of
stomates on the abaxial and adaxial leaf surfaces, high drought score, high
recovery rating, highest NAR at 35 DAP, longest roots, highly vigorous plants,
moderate resistance to cutworm incidence, resistance to leaf curling, bigger leaf
area and leaf area index and more number of vine cuttings that be obtained.
BSU #1 exhibited the lowest drought score, high recovery, produced
longest vine at 50 and 65 DAP, exhibited the biggest leaf area index and leaf
area, highest number of vine cuttings.
Genotype Inubi –Ca produced the highest vine length at 70 and 105 DAP,
biggest leaf area index at 35 DAP, heaviest vine and more number of vine
cuttings.
NSIC 31 exhibited the lowest drought score, highest recovery rating,
highest (NAR) at 35 and 50 DAP and heaviest roots at harvest.
JK 23-1 produced highest RWC, highest NAR at 35 and 50 DAP and
longest vines at 35 DAP.
Taiwan D exhibited more number of stomates on the leaf surface, low
drought score, highest recovery rating, high RWC, high NAR , highly vigorous
plants, shortest vine length, bigger leaf area, and moderate resistance to cutworm
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
and leaf curling.
Plants under severe stress were observed to have small leaf area and leaf
area index, lowest NAR medium roots, lowest recovery rating and highest
drought score.
Plants under moderate stress were noted to have small to medium leaf area
and leaf area index, heaviest roots, longest roots and highest RWC.
Genotypes, four (JOG 11-10, JK 18 - 4, Taiwan D, NSIC 23 and Inubi –
CA) under moderate stress produced highest leaf area, highest NAR and longest
roots. Based on the parameters genotypes JK 18 - 4 and JK 7 - 4 under severe
stress showed the highest drought score and lowest recovery rating.
Out of the 10 genotypes five (JOG 11-10, JK 18 - 4, Taiwan D, NSIC 23
and Inubi - Ca) were observed to have the characters for stress resistance such as
small leaf area and leaf area index, longest roots, low drought score, high
recovery rating and more vine yield.
Leaf area at 65 DAP and root weight were positively correlated to vine
yield. Conversely, drought score was negatively correlated to vine yield.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
1
INTRODUCTION
Background of the Study
Sweet
potato(Ipomoea batatas L. Lam), is considered worldwide as an
indigenous, traditional and subsistence crop. In the Philippines, it is “popularly
known as “camote”, a versatile rootcrop, rich in carbohydrates and other nutrients.
Its roots can be boiled, fried, sweetened, processed into flour for cakes and as part
of feed formulation. Its soft shoots can be prepared as vegetable salad while the
hard stem can be used as feed for pigs, goats and other animals (Larananget al.,
2004).
Sweet potato is high in vitamins A, C, and E, B6, copper, dietary fiber,
manganese, folate, potassium and iron. Varieties with yellow to orange flesh
indicate higher beta-carotene content while those with purple flesh have high
anthocyanin content. As a rootcrop, it has better carbohydrate complex that is
good for diabetics since they are “stabilizers”, not “enhancers”
(http://newsinfo.inquirer.net/inquirerheadlines). Its protein content is half as much
as the common potato but has less sugar (Valdez, 2002).
Sweetpotatois anunder-exploited food crop that ranks fifth among the
food crops after rice, potato wheat and seventh in the world in terms of total
production (FAOSTAT, 2008). About 90% of the world’s production comes from
Asia, and the Philippines ranks fifth next to Vietnam, Indonesia, India and China
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
2
(Huaccho and Hijmans, 2000). BAS in 2003 has recorded Leyte, Camarines Sur,
Bohol, Albay and Quezon as the top five producers of sweet potato in the country.
However,its 2004 report,Tarlac was listed to have the fifth largest hectarage of
sweet potato but has the largest contiguous commercial sweet potato area in the
Philippines (PCARRD, 2006).
Ninety percent of sweet potato produced in the Philippines is used for food,
5% for feed and another 5% for processing. The per capita consumption is only
about 18 kg per year compared to the more than 100 kg per year for rice
(FAOSTAT, 2002).
Sweetpotatois a secondary staple food crop for people living in rural areas,
hilly regions and coastal plains. In Tarlac, sweetpotato is next to rice. Production
of quality storage roots of sweetpotato is important to sustain the emerging
population in the area. However, farmers had difficulties in producing quality
storage roots during summer due to production constrains such as genotypes,
water and temperature.
Sweet potato productivity is limited by a number of both biotic and
abiotic constraints. Water stress is one of the most common environmental
stresses affecting plant growth and productivity (Boyer, 1982). Plant water stress,
often times caused by drought, can have major impacts on plant growth and
development. When it comes to crops, plant water stress can be the cause of lower
yields and possible crop failure (Onyilagha, 2008).
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
3
The main consequence of moisture stress is decreased growth and
development caused by reduced photosynthesis. Photosynthesis is the process in
which plants combine water, carbon dioxide and light to make carbohydrates for
energy. Chemical limitations due to reductions in critical photosynthetic
components such as water can negatively impact plant growth (Farkas, 2004).
Low water availability can also cause physical limitations in plants.
Stomates are plant cells that control movement of water, carbon dioxide, and
oxygen into and out of the plant. During moisture stress, stomates close to
conserve water. This also closes the pathway for the exchange of water, carbon
dioxide, and oxygen resulting in decreases in photosynthesis. Leaf growth will be
affected by moisture stress more than root growth because roots are more able to
compensate for moisture stress (Bauder, 2009).
Drought is a worldwide problem, seriously limiting global crop
production.Recently, global climate change has made this situation more serious
(Pan, 2002). Drought is a complex physical-chemical process, in which many
biological macromolecules and small molecules are involved, such as nucleic
acids (DNA, RNA, microRNA), proteins, carbohydrates, lipids, hormones, ions,
free radicals and mineral elements (Levitt, 1979).
Sweet potato is considered to be moderately drought tolerant (Valenzuela
et al., 2000). However, drought is often a major environmental constraint for
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
4
sweetpotato production in areas where it is grown under rainfed condition
(Anselmoet al., 1998).
Objectives of the Study
Generally, the study was conducted to screen and evaluate sweetpotato
genotypes for water stress.
The specific objectives of the study were to:
1. screen sweetpotato genotypes from various germplasm
sources for drought resistance;
2. determine the effect of water stress on the growth of
genotypes.
3. evaluate the growth and yield of selected sweetpotato
genotypes for drought resistance under greenhouse
condition;
4. determine the interaction effect of sweetpotato genotypes
and levels of water stress; and
5. correlate growth parameters with vine yield of sweetpotato
genotypes.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
5
Importance of the Study
Maintaining and increasing supply of food to the emerging population has
been a challenging problem to the governments because of vagaries in global
climate and the resultant effect on crop productivity. Global climate change
involves a rise in temperature, water deficit stress, high CO2, high UV radiation,
rainfall and others. All of these changes affect (beneficial or detrimental) the
production of plants that are used for food.
Considering the role that sweetpotato plays into food production and
industrial uses, it is paramount to determine genotypes that are resistant to water
stress. The information generated relative to water stress resistance can be useful
in elucidating such resistance in other crops.
Time and Place of the Study
This study was conducted at SitioBakitan, Barangay Nipaco, Paniqui,
Tarlac from May to October 2011.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
6
REVIEW OF LITERATURE
Importance of Sweetpotato
Sweet potato ranks third among the 10 major crops of the world on a
calorie per surface unit basis (Boukamp, 1985). It is the most productive
carbohydrates producing crop and requires less inputs and water compared to rice,
corn and potato. Sweet potato is a good alternative food supplement during the
rice shortage (Zuraida, 2003). It was reported by FAO (1999) that sweet potato
can produce more edible energy per hectare per day than wheat, rice or cassava.
Sweetpotato is excellent source of vitamin A (the more colored the sweet potato,
the more vitamin A it contains), potassium, vitamin C, vitamin B6, riboflavin,
copper, pantothenic acid and folic acid. Higher in starch than potato, it contains
more or less the same amount of carbohydrate and the nutritional information of
sweetpotato per 3.5 oz/100 g are water 73%, protein 1.6 g, fat 0.3g,
carbohydrates 24.3g, fiber 2.5g, and calories 105g (Encarta, 2007).
Water Stress Definition and Characteristics
Water stress occurs when the demand for water exceeds the available
amount during a certain period or when poor quality restricts its use. It causes
deterioration of fresh water resources in terms of quantity (aquifer over-
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exploitation, dry rivers, etc.) and quality (eutrophication, organic matter pollution,
saline intrusion, etc.)(UNEP Freshwater in Europe, 2009).
Water stress is characterized as having insufficient water of satisfactory
quality and quantity to meet human and environmental needs. While many people
are already living in regions facing water stress, it has been estimated that by
2025, the share of the world's population living in water stressed areas will
increase to 35% or about 2.8 billion people. In fact, it is predicted that, in the near
future, there may well be conflicts over water on the same scale as those for oil.
According to the Falkenmark (2001), a country or region is said to
experience "water stress" when annual water supplies drop below 1,700 cubic
meters per person per year. At levels between 700 and 1,000 cubic meters per
person per year, periodic or limited water shortages can be expected.
Definition of Drought
A field definition for drought is a period without rain, of sufficient
duration to cause injury to the crop and significantly reduce the economic yield.
Drought begins when the readily available soil water in the root zone is exhausted
(Kramer, 1983).
Drought stress is the most common adverse environmental condition that
can seriously reduce crop productivity. Increasing crop resistance to drought
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stress would be the most economical approach to improve agricultural
productivity and to reduce agricultural use of fresh water resources (Islam, 2007).
Drought is one of the most common environmental stresses affecting plant
growth and productivity (Boyer, 1982). Polyethylene glycols (PEG) of high
molecular weights have been long used to simulate drought stress in plants as
non-penetrating osmotic agents lowering the water potential in a way similar to
soil drying (Larher et al., 1993).
Drought tolerance refers to the degree to which a plant is adapted to arid
or drought conditions. Desiccation tolerance is an extreme degree of drought
tolerance. Plants naturally adapted to dry conditions are called xerophytes (Levitt,
1979).
Drought is a worldwide problem and a major proportion of agriculture
land is affected with varying degrees of drought. Water deficit, extreme
temperatures and low atmospheric humidity lead to drought, which is one of the
most limiting factors for better plant performance and higher crop yield (Szilgyi,
2003; Hirtet. al., 2003). The repercussions of water deficit include its adverse
effects on plant phenology, phasic development, growth, carbon assimilation,
assimilate partitioning and plant reproduction processes. Drought stress
differentially affects the level of endogenous phytohormones. Phytohormones are
naturally occurring organic substances, which influence physiological processes
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at low concentrations either in distant tissues to which they are transported or in
the tissue where synthesis occurred (Davies, 1995a).
Water plays a crucial role in the survival of all organisms. In plants in
particular, aside from fulfilling the roles of solvent, transport medium and
evaporative coolant, water provides the energy necessary to drive photosynthesis,
the natural plant process which synthesizes organic food. Photoautotrophs are
organisms that posses their own chlorophyll and are able to harness the energy
associated with sunlight, in a process called photosynthesis. Under drought
conditions the loss of water in the plant protoplasm may result in the
concentration of ions in the protoplasm to toxic levels resulting in possible protein
denaturation and membrane fusion and negatively impacting plant metabolism
(Ramanujam, 1985).
Water deficiency is a severe limiting factor in several countries and
impacts on both food production and the economies of these countries.
Approximately four-tenths of the world’s agricultural land is in arid or semi-arid
regions with transient droughts causing death of livestock, famine and social
dislocation. Several agricultural regions are reliant on irrigation to maintain yields.
Climate change has been implicated in the fact that drought areas have more than
doubled in the last thirty years (Somasundaram et al., 2008).
A drought tolerant plant can tolerate a period of time without water. A
drought resistant plant stores water (like a cactus), dies back or goes underground
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(like an ornamental onion) or has mechanisms to protect itself from the harsh
drying sun. Once drought resistant plants are established they can live for very
long periods of time without water( Vajrabhayaet al., 2001).
Mechanism of Drought Tolerance in Plant
Drought tolerant plants typically make use of either C4 carbon fixation or
crassulacean acid metabolism (CAM) to fix carbon during photosynthesis. Both
are improvements over the more common but more basalC3 pathway in that they
are more energy efficient. CAM is particularly good for arid conditions because
carbon dioxide can be taken up at night, allowing the stomata to stay closed
during the heat of day and thus reducing water loss (Levitt, 1979).
Many adaptations for dry conditions are structural, including the
following:Adaptations of the stomata to reduce water loss, such as reduced
numbers or waxy surfaces; water storage in succulent above-ground parts or
water-filled tubers, adaptations in the root system to increase water absorption,
and trichomes (small hairs) on the leaves to absorb atmospheric water.
Gurgel (2008) stated that the indicators to have the ability to survive
during drought condition are deep root system wherein the roots are the main
engine for meeting transpirational demand, and play an important role in
controlling plant water status to avoid drought injury and leaf blades wherein
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leaves which roll under dry conditions, exposing less leaf surface to be in contact
with dry air.
According to Jiyue (2008), the various mechanisms of drought tolerance
in plants.Plants has ways of responding on drought stress, three primary types of
drought tolerance in plants have been identified: (1) drought escape; (2) drought
tolerance of dehydration postonement with high tissue water potential; (3) drought
tolerance of dehydration tolerance with low tissue water potential. Drought
escaping plants, known as desert ephemerals, are of the ability of completing their
life cycle before a serious water stress develops, but their characteristics of
drought escape have not been discussed in this paper. The characteristics of
drought tolerating plants have been concentrated on discussing in this paper. The
main characteristics of drought tolerance in plants that have the ability of
dehydration postponement with high water potential are maintenance of water
uptaker and reduction of water loss. The main characteristics of drought tolerance
in plants which are of the ability of dehydration tolerance with low water potential
are maintenance of turgor and protoplasmic desiccation tolerance.
Save et al. (2005) stated that tolerance and avoidance mechanisms to
drought stress were studied in 6-month-old plants of Newhall orange (Citrus
sinensis (L.) Osbeck) and Ellendale tangor (orange × mandarin hybrid) (Citrus
sinensis (L) Osbeck × Citrus reticulata Blanco) during a drought/rewatering cycle
under controlled conditions. Drought stress did not promote osmotic adjustment,
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while elastic adjustment (tissue elasticity increase) was noted in stressed orange
and tangor plants. Both citrus plants showed a parallel decrease in leaf
conductance (g1) and leaf water potential (Ψ1) under water stress. Tangor plants
had a more efficient water conservative strategy than orange, based on the
characteristics of canopy architecture (lower canopy area and a more closed
canopy with leaves nearly vertically oriented) together with a significant decrease
in cuticular transpiration rates (TRc) under stress.
Mickelbart (2010) stated the leaf characteristic of drought tolerant plants.
Small leaves, leaf waxes, and minimal leaf area all lead to reduced water loss, and
therefore, drought tolerance. The large leaf areas can be detrimental to growth and
survival under conditions of water stress because there is more surface area from
which water can be lost. Therefore, drought-tolerant plants will often have small
leaves or, in the case of conifers, needles that have low surface area. While this is
generally true, there are many plants with large leaf areas that are drought-tolerant,
such as southern magnolia (Magnolia grandiflora), and sycamore (Platanus sp.).
Drought-tolerant plants often accumulate waxes on their leaves or needles.
Waxes are thought to prevent water loss and reflect light, which keeps leaf
temperature from becoming too high.
Leaf hairs (called trichomes) appear as grey or white pubescence and
reflect light and reduce water loss. While we still don’t fully understand how
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trichomes affect plant water loss, leaves that are covered with these small hairs
typically lose less water than those that do not.
According to various researchers the characteristic of drought tolerance
plant are: Aromatic foliage: The essential oils exuded from plants act like a
suntan lotion, which protects the plant from the suns rays; Waxy stems and leaves:
This coating, which can be scraped off with a fingernail, protects the plant against
the sun. Waxy plants also tend to have thick stems and leaves. Silver/grey Foliage
is usually caused by layers of white hairs on the leaf surface. These hairs reduce
water loss by reflecting the sun’s rays and holding moisture; and Hairy foliage
protect the leaves from the sun.
Techniques in Screening for Drought Resistance
Polyethylene glycol (PEG) is a polymer produced in a range of molecular
weights. In 1961 Lagerwerff et al., cited that PEG can be used to modify the
osmotic potential of nutrient solution culture and thus induce plant water deficit in
a relatively controlled manner, appropriate to experimental protocols. It was
assumed that PEG of large molecular weight did not penetrate the plant and thus
was an ideal osmoticum for use in hydroponics root medium.
During the 1970’s and 1980’s, PEG of higher molecular weight (4000 to
8000) was quite commonly used in physiological experiments to induce
controlled drought stress in nutrient solution cultures. Several papers also reported
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theoretical or measured concentration-osmotic potential relations for PEG of
different molecular weights (e.g.Money, 1989; Michel, 1983; Michel and
Kaufmann, 1973). Experience gained by users indicated that these relationships
can diverge to some extent depending on the lot or source of the specific PEG
used. It is therefore advisable to measure the actual osmotic potential of the
solution culture containing PEG.
Hsissouet al. (1994) stated that polyethylene glycol 10000 (PEG), which is
a non-toxic hydrosoluble polymer, is used in the in vitro culture medium for
drought-resistance selection. PEG stimulates water stress by reducing the free
water in the extracellular medium and the water available to the cells.
According to Munir andAftab (2009), PEG (polyethylene glycol) has
been used in vitro to induce water stress in plants. It is a non-penetrating inert
osmoticum that lowers the osmotic potential of nutrient solutions, but it is not
taken and is not phytotoxic. PEG stimulates water stress in cultured plant cells in
the same way it does in the cells of intact plants.
Sakthiveluet al. (2008)cited that polyethylene glycols (PEG) of high
molecular weights have been long used to simulate drought stress in plants as
non-penetrating osmotic agents lowering the water potential in a way similar to
soil drying. According to Hassanpanah (2010), polyethylene glycol (PEG) 6000
was used for exerting the water deficiency stress on the plantlet.
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Polyethylene glycol, a non penetrable and nontoxic osmotic, lowers the
water potential of the medium and has been used to simulate drought stress in
plants. Cells adapted to PEG caused deficit of water have been isolated in
Lycopersiconesculentum. ( Bressanet al.,1981; Handa et al.,1982, 1983).
Badianeet al.(2003) stated that effects of water deficit induced by
polyethylene glycol-6000 on some cowpea varieties showed that the lateral roots
number were reduced with 3.8 fold compared to control. Inadequate water
availability is a crucial limitation to crop growth and yield (Boyer, 1982).
Hamayunet al. (2010) mentioned that polyethylene glycol (PEG)
solutions of elevated strength (8% & 16%) were used for drought stress induction.
Drought stress period span for two weeks each at pre and post flowering growth
stage. It was observed that soybean growth and yield attributes significantly
reduced under drought stress at both pre and post flowering period, while
maximum reduction was caused by PEG (16%) applied at pre flowering time.
Kulkarni and Deshpande (2007)stated that using PEG in screening tomato
germplasm under in vitro condition decreased seedling growth with increasing
concentration of PEG indicating precise nature of the in vitro screening. Mutant
hybrid and its derivatives were observed with outstanding ability to continue root
growth under in vitro stress conditions indicating their ability to fight severe water
stress situation.
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Bayoumiet al. (2008) stated that drought stress in laboratory experiment
were induced by polyethylene glycol (PEG) (0, 15 and 25%, with three replicates)
and applied on germination of wheat genotypes seeds. The PEG induced a drop in
the shoot, root biomass and coleoptiles length which was the greatest in genotypes
3, 4 and 9, while the decrease in genotypes 1,2 and 6 was little under the various
levels from PEG. The variability of leaf proteins was analyzed by sodium dodecyl
sulphate polyacrylamide gel electrophoresis (SDS-PAGE). It is concluded that
leaf protein profiles could be useful marker in the studies of genetic variation and
classification of adapted cultivars under control and stress conditions.
Trachselet al. (2011) stated that the application of PEG 8000 in corn
plants at concentrations higher than 10% (osmotic potential of 0.14 MPa) led to
reductions in elongation rates of both lateral (kLat) and axile roots (ERAx). At
concentrations of 40% axile root growth was almost stopped completely after six
days of treatment, while lateral root growth was strongly reduced and the
application of 25% PEG8000 resulted in reductions of ERAx by 38% and 58%
compared to the well watered control for P2 and CML444, respectively. ERAx for
P1 was barely altered in response to desiccation stress, indicating physiological
tolerance of desiccation stress.
Abdel-Raheem et al. (2007) showed that using different concentrations of
PEG in the medium showed a great effect on the growth value at the end of 30
days growing period. The mass of callus and shoots regenerated directly from
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explants were evaluated after 60 days of growing on regeneration MS medium
supplemented with different concentration of PEG. The highest dry weight was
achieved when the Peto-86 explants were cultivated on MS supplemented with
75.00 gram PEG. Shoots regeneration frequency of cotyledon segment of tomato
genotype ranged from 12.00 to 82.40 %.
Mathekaet al. (2008) stated that using PEG 18-20% concentration in
maize calli was found out that selected had lower survival and regeneration
capacities than unselected calli. The survival percentages of maize calli grown in
mannitol at PEG were 0.4 and 4.2 %, respectively. Six plantlets were
regenerated from mannitol – tolerant calli, while only two plantlets were
generated from the PEG tolerant calli.
Tusharet al. (2010) studied the use of PEG – 6000, with increasing
concentration of (30, 60, 90, 120 and 150 g/l) in Jatropha seedlings to study its
effect on growth parameters. The root growth, number of secondary roots, true
leaf expansion at morphological level and palisade mesophyll height, xylem
vessel expansion at anatomical level showed drastic negative impact as compared
to control. It is worth to note that local germplasm performance was categorized
into susceptible group as compared to tolerant genotype indicating need for
genetic improvement.
According toVajrabhayaet al. (2001), the four drought tolerant RD23 rice
lines were selected from somaclonal variants arising in vitro. They had been
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selected under the drought condition for 5 generations before the progenies were
used for the experiments. After five weeks in the nutrient solution containing 150
g/L PEG6000, the six-week old drought-tolerant seedlings had approximately 4-
fold increase in total soluble sugar content, while the original drought sensitive
line had only 2.5-fold, when compared with the non-stressed plants. Proline
content was also determined in these rice lines. After five weeks of drought
treatment, nine-to fifteen-fold increase in proline content was detected in the
drought tolerant lines, while the original line had approximately five-fold increase
in proline content. These data suggested that the ability to accumulate the solute
contributes to better performance in drought-tolerance.
Govindarajet al. (2010) stated that pearl millet is one of the most
important cereals grown in drought-prone areas and is the staple grain for millions
of people in West Africa and India. Breeding for drought-prone environments is
constrained by lack of suitable selection indices of drought stress resistance. The
present study is conducted to determine the reliability of in vitro screening
method for initiating drought breeding programme. This in vitro screening
method proves to be an ideal method for screening large set of germplasm with
less efforts accurately and cost effective. This experiment was carried out with a
collection of twenty one millet genotypes including commercial varieties and
advance hybrid cultures tested in completely randomized design. Data were
recorded at five different moisture stress levels (-3, -5, -7.5, -10 bars and control)
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by using polyethylene glycol (PEG) 6000 on germination percentage, root length,
shoot length, root / shoot ratio and statistically analyzed for significant differences.
The genotypes recorded significant differences for all traits in response to various
moisture stresses. The genotype TNBH 0538 gave the good germination
percentage, root length, shoot length, and root/shoot ratio as compared with
commercial cultivars under all five moisture stresses. ICMV- 221 showed highest
resistance against moisture stress, while PT6034 showed lowest resistance. TNBH
0642 also gave the better performance under all four moisture levels for most of
the traits at seedling stage. The regression studies indicated, the osmotic stress
were the most suitable method for drought tolerance screening owing to their
highly significant relationship with declining root length (R2 = 0.991; P < 0.001)
and shoot length (R2 = 0.998; P < 0.001).
Martinez et al. (2005) stated that water stress reduced CO2 net
assimilation rates quantified in the presence of high CO2 and low O2 levels (A),
stomatal conductance and transpiration, but NaCl improved water use efficiency
of PEG-treated plants through its positive effect on A values, especially in young
leaves. PEG increased the internal Na1 concentration. The resistant cell line
accumulated higher concentration of Na1 than the PEG-sensitive one. The
complete absence of Na1 in the medium endangered the survival of both cell lines
exposed to PEG. Although Na1 by itself contributed only for a small part to OA,
NaCl induced an increase in proline concentration and stimulated the synthesis of
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glycinebetaine in response to PEG in photosynthetic tissues. Soluble sugars were
the main contributors to OA and increased when tissues were simultaneously
exposed to PEG and NaCl compared with PEG alone, suggesting that Na1 may
influence sugar synthesis and/or translocation.
Uni-green technique
Uni-green technique is a technique of screening a drought resistant plant
using Polyethylene Glycol (PEG) where in single nodes of sweetpotato were used
as planting materials and planted to a floral foam. Floral foam composition is
nontoxic, environmentally friendly, has improved absorption/adsorption and
retention of liquids, is not as hard as prior art foams, does not include
polymerization by-products detrimental to flower and plant life, and is a foamed
mixture of a caustic silicate solution derived from the caustic digestion of rice hull
ash having diffused activated carbon particles from thermal pyrolysis of rice hulls.
Concept of Soil Matric Potential or Tensiometer
The concept of Soil Matric Potential (SMP) was the water is in contact
with solid particles (e.g., clay or sand particles within soil),
adhesiveintermolecular forces between the water and the solid. The forces
between the water molecules and the solid particles in combination with attraction
among water molecules promote surface tension and the formation of menisci
within the solid matrix. Force is then required to break these menisci. The
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magnitude of matrix potential depends on the distances between solid particles—
the width of the menisci and the chemical composition of the solid matrix.
Soil Matric Potential or moisture content of the soil was measured
through the use of irrometer (soil moisture measurement is based on the
tensionmetric method, because of the fact that the amount of water is not as
important as how difficult it is for the plant to extract it from the soil) with a unit
in centibars (cb) an instrument that operates on the tensiometer principle,
installation was done a month after planting (Tensiometerquick start guide,
2010).
Studies on Drought Tolerance in Different Crops
Water deficit is a common stress in potato production, which leads to the
tuber quality and yield reduction . Because of potato susceptibility to drought
preparing sufficient water is very important for increasing potato quality and
quantity (Hassanpanahet al., 2008).
Ferreria (2002) cited that in hot dry climates, high evaporative demand
increases crop water requirements, which may compound the sensitivity of the
crop to water stress, resulting in greater yield reductions than experienced with
similar water deficits under cooler conditions.
According to several researchers, vegetables crop water requirements
range from about 6 to 24 inches (15 to 60 cm) per season, and precise irrigation
requirements can be predicted based on crop water use and effective precipitation
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values. Since potato has a shallow root system, normally 70 percent of the total
water uptake occurs from the upper 30 cm soil depth and 100 percent from the
upper 40 to 60 cm soil depth (FAO, 2001).
King and Stark (2004) noted that water is necessary after emergence,
early vegetative stage when stolon and tubers are formed up to tuber
enlargement while Ferreria (2002) stressed that potato should be irrigated as
even as possible, particularly at 4 to 9 weeks after emergence when the tubers
are forming to avoid tuber skin cracking and malformation. Nimahet al. (2000)
stated that irrigation below 53% evapotranspiration (ET) causes a reduction in
non- marketable tubers as well as physiological abnormalities.
Al-Taisan (2010) stated that water stress due to drought and salinity is
probably the most significant abiotic factor limiting plant and also crop growth
and development. Salinity and drought stresses are physiologically related,
because both induce osmotic stress and most of the metabolic responses of the
affected plants are similar to some extent. Water deficit affects the germination of
seed and the growth of seedlings negatively. Temperature is an exceedingly
important factor in seed germination. It directly affects whether a plant can sprout
and, if so, how long it will take to emerge from the ground.
Saraswatiet al. (2003) cited that sweetpotatoplant’s biomass, main stem
length, internode length and diameter, leaf number and area, and root weight
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decreased and leaf water potential decreased significantly in response to water
stress.
MFAI (2006) mentioned that yield is greatest when soil moisture is
maintained above 65% of the soil available water capacity because more tubers
are set and therefore, tuber set is particularly sensitive to moisture stress.
Likewise, several studies showed that water stress during tuber set and early
bulking growth stages causes the greatest reductions in tuber yield and quality
since few but larger tubers are produced while dry soil conditions in later stage
reduces yield and specific gravity, shortens dormancy (ICPRE and UI-CALS,
2002) and increases reducing sugar content of tubers (ICPRE and UI-CALS,
2002 )
Jose et al. (2008) cited that potato clones with high leaf number at 40
DAP, less vines at 55 DAP, early bulking ability, high harvest index and good
canopy cover were high yielding under drought condition.
Varietal Evaluation of Crops for Drought Resistance
Potato
Yadavet al. (2003) studied the effect of irrigation on growth and yield of
potato cv. Kufri Sutlej. Data revealed significant difference in the plant height due
to irrigation levels and maximum reduction in plant height was observed at CPE
of 100 mm in both years comparedto other treatments.
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Vegetables
Upretiet al. (2000) studied the response of pea cultivars to water stress.
The results revealed that pea cultivars differed widely in vigour under the
conditions of moisture stress. There was significant reduction in plant height in all
the cultivars and the effect of moisture stress was more pronounced at vegetative
stage than at flowering stage.
Hegde (1988) studied the effect of irrigation regimes on growth of sweet
pepper. Data revealed that when the soil matric potential reached -85 kPa plant
height reduced significantly during both years of 1984 and 1985 (42.1 and 40.8
cm, respectively) as compared to those irrigated between -25 to -65 kPa which
were on par among themselves.
Kushwahaet al. (2003) studied the drought tolerance in chickpea
genotypes. They reported, general reductions in plant height in all the genotypes
under rainout shelter conditions as compared to rainfed condition, which indicated
higher intensity of stress realization in rainout shelter. Maximum reduction in
plant height was noticed in BG-362 (- 18.00) and ICC-4958 (-17.00).
Rana and Kalloo (1989) studied the morphological attributes associated
with the adaptation under water deficit condition in tomato. Data revealed that,
resistant genotype L. pimpinellifoliumrecorded highest plant height (140 cm)
compared to other resistantgenotypes, where as susceptible genotype, KS-54 had
recorded least plant height (49.60 cm). When plants were watered biweekly there
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was significant reduction in the plant height (18.90 cm) compared to daily
watering (38.50 cm) as reported by Milton et al. (1992) in tomato.
Rad and Sree Vijay (1991) studied the moisture stress effect at different
morphological stages on growth and yield of tomato cultivars. They reported that,
different genotypes responded variedly for plant height under moisture stress.
Moisture stress at all the stages i.e., vegetative stage, 50 per cent flowering stage
and fruiting stage reduced plant height very significantly. Moisture stress imposed
at vegetative growth stage resulted in maximum reduction in plant height (68.56
cm) when compared to control (86.08 cm).
Subramanian et al. (1993) while, studying the influence of moisture
regimes on growth of brinjal, reported significant differences in the plant height at
different growth intervals. Maximum reduction was observed at the IW/CPE ratio
of 0.4 at all growth stages compared to other irrigation regimes while,
significantly higher plant height was observed in the irrigation regime of 1.0
IW/CPE ratio at all the growth stages. Differential irrigation levels revealed
reduction in the plant height in brinjal. Maximum plant height was recorded at 1.2
evapo-transpiration (59.8cm) compared to other treatments and minimum was
recorded in 1.0 evapo-transpiration (50.2 cm) as reported by Manjunathaet al.
(2004) in brinjal.
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Subramanian et al. (1998) concluded that, irrigation at 0.90 IW/CPE ratio
responded positively and registered significantly higher plant height in chilli as
compared to other irrigation levels of 0.75, 0.60 and 0.40 IW/CPE ratios.
Thakur et al. (2000) studied the effect of water deficit on growth of chilli.
They reported that due to water deficit conditions there was reduction in the plant
height and maximum reduction was observed under 75 per cent water deficit (6.0
cm) compared to control (9.1 cm).
Kushwahaet al. (2003) studied the relationship of drought tolerance with
number of branch per plant of chickpea. They reported that there was maximum
reduction in the number of branches in K-850 (23.00) and IPC-94-132 (20.50)
under rainout shelter condition compared to rainfed condition and there was no
reduction in number of braches in BG-362 under rainout shelter compared to
rainfed condition.
Gopalkrishnaet al. (1996) reported that in linseed, when irrigation level
was induced at 0.8 IW/CPE ratio up to 75 DAS resulted in significantly higher
primary braches (6.1) andwas on par with that of delayed irrigation at o.4 IW/CPE
ratio up to 75 DAS, similarly, thenumber of secondary branches were
significantly higher when irrigation was scheduled at 0.8IW/CPE ratio throughout
crop growth (20.86) and minimum was observed in irrigation at 0.4IW/CPE ratio
(16.08).
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Manjunathaet al. (2004) studied the effect of irrigation schedule on
vegetative growthof brinjal and found maximum number of branches per plant at
1.2 IW/CPE ratio (10.0)compared to the minimum number observed under
IW/CPE ratio of 1.0.
Sweetpotato
In sweetpotato, clones with high leaf number at 40 DAP, less vines at 55
DAP, early bulking ability, high harvest index and good canopy cover were high
yielding under drought condition (Anselmo, 1992)
Kelm et al. (2000) stated that sweetpotato genotypes with small canopies
were associated with a consistently positive response in their final storage root dry
matter (DM) yields to increasing N supply, and with efficient allocation of DM
and N to storage roots. Genotypes with high canopy net assimilation rates (NARs)
had a high proportion of leaves exposed to the sun and high chlorophyll content in
leaves. Nitrogen stress led to increased transpiration per unit leaf area and
decreasing WUE. Decreasing WUE under N stress was due to lower total plant
DM production rather than to increased total water transpiration per plant.
Although sweetpotato can survive severe moisture stress conditions,
marketable yield is adversely affected. The variety W-119 outperformed the other
varieties during severe moisture stress, with Resisto identified as very sensitive to
moisture stress. Variety Isondlo has the ability to use water very efficiently at all
irrigation levels showing promising results regarding yield and water usage
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effiency (WUE). Significant differences were observed in shoot development, leaf
area index, marketable yield and stomatal conductance between the varieties and
the treatments. Severe water stress resulted in closure of stoma and exhibited
dramatic decline in photosynthetic/transpiration rate. It also demonstrate a large
set of parallel changes in the morphological, physiological and biochemical
processes when the varieties were exposed to drought stress (Laurietet al., 2009)
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29
MATERIALS AND METHODS
This study composed of two experiments, first was the screening of 40
sweetpotato genotypes using the Uni-green technique under room temperature;
and thesecond is the evaluation of ten selected genotypes for drought resistance
under greenhouse condition.
Experiment 1: Screening of Sweetpotato GenotypesUsing Uni-Green Technique
Germplasm
Forty genotypes of sweetpotato were used in this study. The genotypes
used were initially observed to have variability in their morphological
characteristics for them to have been included for the screening. The
sweetpotatogenotypes and their morphological characteristics are described in
Table 1.
Establishment of mother plants
Cuttings were planted in 8 x 8 x 14 inches polyethylene bags with sandy
loam soil and decomposed cow manure at a ratio of 2:1 v/v.
The previously planted sweetpotato cuttings whichserved as mother
plants, were raised inside the nursery. Irrigation, fertilization, pest and disease
control measures were applied to the plants for fast growth.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
30
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
31
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
32
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
33
Experimental design and treatments
The 40 x 2 study was laid out in Completely Randomized Design (CRD)
following the involving two factors;(genotypes designated as Factor A (Table 1)
and water stress level as Factor B) and replicated three times. Ten sample plants
per replicate were considered; a total of 2,400 thus,
Factor A consisted of 40 genotypes (as earlier described in Table 1)
Factor B levelinvolved the two of water stress or soil matric potential
L1 – normal condition (20 cb)
L2 –moderate stress(60 cb)
Soil moisture potential (SMP) in centibars (cb) was measured with the use
of an irrometer, operating similarly on the tensiometer principle.
Preparation of plantingmaterials
Ten cmlong nodal cuttings or cuttings with 7 nodes with newly
developed leaves were obtained from healthy sweetpotato plants. The single node
cuttings ofsweetpotato were collected between 7:00 to 8:00 A.M. while the
tissues were still fresh.
The cuttings were washed with soap and Benomyl at the recommended
rate. and were rinsed three times using purified water.
Screening And Evaluation Of Sweet potato Genotypes
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34
Preparation of floral foam and single-node planting materials
Floral foam measuring 2.5 cm x 3.5 cmx 2.75 cm with a weight of 0.71 g
was used as a medium or holder. The foam contains mixture of caustic silicate
solution derived from the digestion of rice hull ash having diffused activated
carbon particles from thermal pyrolysis. Floral foams were placed in each cell of
the seedling tray. About 31.5 ml purified water was used to water each floral
foam. The weight of the floral foam after watering was 26.16 g.
Single nodes with healthy buds were obtained from sterilized nodal
cuttings of sweetpotato vines. The sterilized planting materials were planted in a
floral foam late between 4:00 to 6:00 P.M. Planted single node cutting were
maintained in a seedling tray for a month (Figure 1).
Fertilizer application
The fertilization recommendation of 20 N – 20 P2O5 - 20 K20 was used
as foliar fertilizer at a rate of 70g li -l of water.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
35
Figure 1.Sweetpotato single nodal cuttings were one week after planting in floral
foams
Drought stress imposition
A month after planting or when the plantlets had about 7 cm of roots
and shoots with at least three nodes, the plantlets wereimmersed in purified
water with 20 mg –lof polyethylene glycol 4000 (PEG) for 5 minutes on the first
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
36
day of treatment. In the succeeding days, immersion was reduced to 2 minutes.
Immersion was done twice.
The data gathered were:
A. Morphological Parameters
1. Number of stomates. Leaf samples were obtained from the middle portion
of the canopy at 9:00 AM. Nail polish was slowly brushed over the surface
of the leaf, air dried and covered with scotch tape. After 20 minutes, the
scotch tape was slowly removed, taking the epidermis,then mounted on a
glass slide and observed under the microscope with installed grid of one
square cm at 40 x magnification. The stomates on the adaxial and
abaxialsurfaces were counted and described.
2. Leaf orientation. Leaf inclination was observed during the cropping period
and characterized whetherplanophyle or erectophyle.
3. Leaf reaction to moisture deficit. The leaves of the different varieties were
observed if curling, drooping or shedding as a result of moisture deficit.
4. Leaf area (cm2). At 35 days after planting, thearea per leaf was calculated
based on the Tracing Technique method of Saupe (2006). Ten selected
leaves from the bottom, middle and top portions of five samples were
obtained, tracing on a coupon band, cutout and weighed. The area per leaf
was taken using the formula:
Area per leaf (cm2) = Weight of leaf tracing (g) x Conversion factor(cm2-g-1)
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
37
Area of coupon bond (cm2)
Conversion Factor (cm2-g-1) =
Weight of coupon bond (g)
The average area per leaf was obtained by adding the leaf areas divided by
the number of traced leaves.
5. Length of roots (cm). The roots of ten plantlets were measured.
6. Number of roots. The roots produced by 10 plantlets were counted.
7. Length of shoots (cm). The shoots of the plant were measured before and
after exposing them to stress.
B. Physiological Parameters
1. Drought score. A week after the application of PEG, visual observation on
the plant canopy was recorded using the rating scale (CIP, 1991) as:
Score Description
1
No stress or all the leaves are turgid in all plants
3
30% of the leaves wilted or 30 % of the plant population is wilted
5
50% of the leaves wilted or 50% of the population is wilted
7
80% of the leaves wilted or 80% of the plant population is wilted
9
Complete wilting and death of plants.
2. Recovery rating. Upon noting the drought score, the plants were watered
and after 24 hours, recovery rating was taken using the scale by Beckman
(1980) as cited by Jose and Tad-awan (2008) as follows:
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
38
Score Description
1
No recovery
3
30% of the leaves recovered
5
50% of the leaves recovered
7
80% of the leaves recovered
9
Complete recovery of the plants
3. Relative Water Content (RWC).After 45 days from planting (DAP) 10
leaves each from two sample plant, were taken at the middle portion from
the plant canopy at about 9:00 to 10:00 A.M. and weighed immediately.
The leaves were then immersed in tap water for 4 hr to obtain the turgid
weight and oven dried at 70 oC until crispy.
Fresh weight of leaves – oven dry weight of leaves
X 100
Turgid weight of leaves –
RWC =
Oven dry weight of leaves
C. Growth Parameters
1. Percentage survival.The number of surviving plantlets was counted and
expressed in percentage using the formula:
Number of explants that survived
% Survival =
X 100
Total number of explants planted
2. Plant vigor. Plant vigor was noted 30 DAP based on the rating scale by
Coffey (1999 ) as:
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
39
Scale Description Reaction
1
Plants are weak with few stems and
Poor vigor
leaves; very pale
2
Plants are weak with few thin stem and
Less vigorous
leaves; pale
3
Plants are better than less vigorous
Moderately vigorous
4
Plants are moderately strong with robust
Vigorous
stems
5
Plants are strong with robust stems and
Most vigorous
leaves: light to dark green in color
3. Height increment (cm). Plant height was measured everyafter ten days.
Measurement was obtained from the base of the plantlets to the tip of the
leaf.
Experiment 2.Evaluation of Selected Genotypes for Drought Resistance under
Greenhouse Condition
The 10 selected sweetpotato genotypes derived from Experiment 1 were
usedto further evaluate for drought resistance under greenhouse condition. The
characteristics of the 10sweetpotatogenotypes considered drought resistant are
presented in Table 2.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
40
Table 2. Ten genotypes selected from Experiment 1 with their morphological,
physiological and growth characteristics
RELATIVE
LENGTH
GENOTYPE
LEAF
DROUGHT
WATER
ROOT
OF
AREA
SCORE*
CONTENT
NUMBER ROOTS
(cm2)
(%)
(cm)
BSU # 1
23.97
1.00
31.48
17.00
8.30
JK 7-4
56.78
1.00
28.92
12.00
7.97
JK 18 -4
23.97
1.00
27.43
11.00
8.18
JK 23 -1
32.17
1.00
20.68
9.00
8.81
JOG 11-10
20.19
1.00
33.96
19.67
7.86
MBE-SP
92.74
1.00
43.73
8.00
10.27
NSIC- 23
32.80
1.00
32.35
10.00
7.44
NSIC- 31
101.57
1.67
29.60
7.33
5.24
Taiwan -D
26.50
1.00
30.55
9.00
7.34
UBE- CA
34.07
1.00
29.19
10.00
8.28
* Rating scale: 1-no stress; 3-30% of the leaves wilted; 5- 50% of the leaves
wilted; 7- 80% of the leaves wilted ; 9 – complete wilting
Experimental design and treatments
The 10 x 3 factor factorial in randomized complete block design
(RCBD) was usedreplicated three times with 10 samples plants per treatment.
The 10 genotypes presented in Table 2 were assigned as Factor A and three
levels of water stress were assigned as Factor B as follows:
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
41
Factor A – Sweetpotato Genotypes
Factor B – Level water stress
L1- control /normal (20 cb)
L2- Moderate stress (60 cb)
L3 - Severe stress (80 cb)
Crop establishment
Plantlets of selected genotypes were planted in 8 x 8 x 14 inches
polyethylene bag. Polyethylene bags were filled with 12 kg mixture of three
parts of sandy loam soil (sterilized) and one half part vermicompost. Plantlets
were irrigated after planting. To ensure growth and development of the crops,
fertilization was done using complete fertilizer (14 N -14 P205-14 K20) at 15 g
per pot in split application where 5 g was applied at planting and 10 g after one
month planting.
Drought imposition
All treatment combinations were watered regularly and evenly with two
liters of water per pot for four weeks until the crops were established.
From the initial reading of 20 cb (normal ), watering was withheld until
SMP was dropped to 60 cb and 80 cb then watering was done; to attain (60 cb
and 80 cb) 1500ml and 2100 ml of water, respectively,were added. The
procedure was repeated for several times up to one week before harvesting.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
42
Control of insect pest, diseases
Spraying of pesticide was done once a week or as the need arised. Hand
weeding was done every two weeks.
The data gathering were:
A. Meteorological Data
1. Temperature (0C). This was taken by using a thermometer. Temperatures
were recorded inside of the improvised greenhouse.
B. Morphological Parameters
Procedures on data gathering on morphological parameters such as
number of stomates, leaf orientation and leaf reaction to moisture deficit were
described in Experiment 1.
1. Storage roots reaction to sweetpotato weevil. Roots of the different
varieties were observed for the was presence of weevil.
C. Physiological Parameters
The procedures in gathering data on physiological parameters such as
drought score, recovery rating and relative water content were describe in
Experiment 1.
1. Net Assimilation Rate (NAR). Data on leaf areas at 35, 50, and 65 days
from planting were used in the computation of NAR. Two whole plant
samples were uprooted and cleaned. Storage roots were thinly
sliced,including the stems, leaves and roots oven dried at 70oC until
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
43
crispy. NAR was calculated as the total dry matter production per unit
leaf area per day of growth duration (modified Gardner,1985) cited by
Jose and Tadawan (2008) as:
InW2-InW1___
NAR (g/cm2 /day) =
(T2-T1) (LA2-LA1)
Where: W = Total dry matter wt of plant samples (g)
T= Time lapse (days )
LA= Leaf area ( cm2)
In = can be located in scientific calculator
D. Growth Parameters
The procedures on gathering of growth parameters such as
plantvigor,vine length,leaf area, root weight and root length were discussed in
Experiment 1.
1. Number of vine cuttings. This was the total number of vine cuttings
2. Vine Weight. This was the total weight of vines.
3. Leaf area Index (LAI). Areas per leaf at 35 , 50 and 65 DAP were used
to calculate LAI. The average area per leaf was multiplied by the
number of expanded leaves per plant. Likewise, ground area was noted
by measuring the size of the pots. Ratio of the leaf surface to the ground
area occupied by the plant was computed as:
___leaf area(cm2)_
LAI =
Ground area (cm2)
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
44
E. Incidence of Pest and Diseases
1. Insect Pest Incidence. Insect pests were identified and observed during
the cropping period using the rating scale (CIP, 2001) as cited by Jose
andTadwan (2008).
Score Description
1
No apparent injury
2
Injury confined to youngest leaves
3
Some older leaves injured
4
Over 50% of the leaves injured
5
Over 90% of the leaves injured
2. Disease incidence. Diseases were identified and observed during the
cropping period using The scale byKemeraittet al., 1981.
Score Description
0 No
disease
1
Trace to 5% infection
2
5-15%
4
35 to 67%
5
67.5 to 100%
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
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Statistical Analysis
All data were tabulated and analyzed using the appropriate analysis of
variance for two factor factorial in Completely Randomized Design for
Experiment 1, two factor factorial in Randomized Complete Block Design for
Experiment 2. Significance among treatment means was analyzed using the
Duncan’s Multiple Range Test (DMRT). Correlation analysis was also done.
The degree of relationship between two variables was measures using the
Pearson product moment correlation coefficient (R) which characterizes the
independence of X and Y (Amid, 2005). The coefficient R is a parameter which
can be estimated from sample data using the formula:
N ∑xy – (∑x)(∑y)
R =
[ n∑ x 2 – (∑x) 2] [ n∑ y 2 – (∑x) ] 2
Screening And Evaluation Of Sweet potato Genotypes
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46
RESULTS AND DISCUSSION
Experiment 1. Screening of Sweetpotato Genotypes using Uni-green Technique
Morphological Parameters
Number of Stomates on the Abaxial Portion of Leaves
Effect of genotype. Significant differences were noted on the number of
stomates on the abaxial portion of the leaves. Genotype JK-18-4 had the highest
number of stomates cm2 -1 while the least was observed in genotype UPLSP-3.
Other genotypes had stomates cm2 -1 ranging from 53 to 121.67 (Table 3).
Stomatal number is a genotype characteristic but the stomatal opening and
closing are more important to affect transpiration (Jose and Tad-awan, 2008).
Furthermore, the plant leaves lose water primarily by evaporation through the
stomata. The stomatal density depends upon plant species, and can be related to
the plant-ecotype stomata mm-1 (Rowland-Bamford et al., 1990).
Effect of water stress level. Number of stomates on the abaxial portion
of leaves was significantly affected by the level of water stress. In all genotypes,
subjecting plants to moderate stress condition increased the number of stomates.
Genotypes not stressed (20 cb) showed lesser stomates-1cm2.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
47
Table 3. Number of stomates on the abaxial and adaxial leaf surface (cm2) of
the 40 sweetpotato genotypes as affected by water stress level
NUMBER OF STOMATES
ABAXIAL
ADAXIAL
GENOTYPE NO
MODERATE
NO
MODERATE
STRESS
STRESS
G-MEAN
STRESS
STRESS
G-MEAN
(20 cb)
(60 cb)
(20 cb)
(60 cb)
BSU # 1
88.00 h 97.33
h 92.67g
17.27 a-g 18.24
a-e
17.76 b-e
Bureau – N
76.00 n
79.00 o 77.50m
16.41 d-I 16.57
d-g
16.49 e-h
Haponita
112.33 c
122.33 c
117.33cd
13.49 kl 14.28
j 13.39
k
Inubi –BS
118.67 b
124.67 b
121.67b
15.44 f-k 16.13
e-I
15.79 f-I
Inubi – Ca
96.33 ef
108.33 e
102.33e
14.50 h-l 16.62
d-g 15.56
g-j
Inubi- N
70.00 p 73.00
q 71.50o
17.13 a-g 17.30
a-f
17.21 c-g
Japanese Inubi
69.33 p 73.67
q 71.50o
15.86 e-k 16.37
e-h
16.11 e-i
JK -7-4
69.67 p 88.00
klm
78.83lm
14.94 g-l 16.56
d-g
15.75 f-I
JK-18-4
136.33 a
143.67 a 140.00a
14.29 i-l 16.39
e-h
15.34 hij
JK- 23-1
81.00 kl 86.67
lm
83.83k
13.46 kl 13.87 ij 13.66
k
JO6-30-3
111.00 c 114.00
d
112.50d
14.99 g-l 15.92
e-i 15.46
hij
JOG- 11-10
116.67 b 121.67
c
119.17c
16.33 d-I 17.73
a-f
17.03 d-h
JO6-11-22
78.00 mn
82.33 n 80.17l
17.52 a-f 17.86
a-f
17.69 b-e
MBE –SP
72.67 o 120.67c
96.67g
13.62 kl 15.47
f-j
14.55 ijk
NSIC 23
62.67 s
80.67 no 71.67o
15.31 f-l 15.85
e-I
15.58 g-j
NSIC 24
68.00 pq 82.00
n 75.00n
17.26 a-g 17.47
a-f
17.36 b-f
NSIC 28
82.00 k 86.00
m
84.00k
19.49 a 19.29
ab
19.39 a
NSIC 29
66.00 qr
73.67 q 69.83op
19.00 abc 19.03
a-d
19.02 ab
NSIC 31
65.67 qr
85.67 m
75.67n
12.99 l 13.36
j 13.18
k
NSIC -31 BSU
101.00 d
104.67 f
102.83e
17.49 a-f 17.58
a-f
17.54 b-e
SG-02-06-02
85.00 ij 89.00
kl 87.00i
14.38 h-l 14.76
g-j
14.57 ijk
SG-02-13-02
85.00 g
101.67 g
93.33h
15.55 f-k 15.50
f-j
15.53 g-j
SG-02-05-01
92.00 hi
96.67 h 94.33h
16.18 d-j 16.18 e-i 16.18
e-I
SG-98-6-02
86.33 n 90.33
jk
88.33j
16.23 d-j 16.86 b-g
16.55 e-h
SG-02-07-05
76.00 n 79.00
o 77.50m
16.79 c-h 17.30
a-f
17.04 d-h
SG-03-39-01
88.00 h 91.67
ij
89.83i
16.35 d-I 16.94
b-g
16.65 e-h
SP-30-03
94.67 f 98.67
h 96.67g
18.23 a-e 18.90
a-d
18.57 a-d
Super bureau B
79.00 lm 82.00
n
80.50 l
16.22 d-j 16.76
c-g
16.49 e-h
Super Bureau –N 97.00 ef 103.00 fg
100.00f
17.39 a-g 17.7
a-f
17.55 b-e
Taiwan- D
70.00 p 74.00
q 72.00o
16.69 c-I 16.66
c-g
16.68 e-h
Taiwan- R
88.00 h
92.67 ij
90.33i
18.89 abc 19.13
abc
19.01 ab
UPLB SP 1
69.00 p 72.67
q 70.83op
16.61 c-i 17.32
a-f
16.96 d-h
UPLB SP 2
83.33 jk 87.00
lm 85.17k
13.84 jkl 14.09
hij
13.97 jk
UPLB SP 3
50.00 t 53.33
s 51.67pq
17.70 a-f 17.69
a-f
17.70 b-e
UPLB SP 4
69.00 p
73.67 q
71.33o
19.43 ab 19.58
a 19.50
a
UPLB SP 5
50.00 t
56.00 r
53.00 p
17.53 a-f 17.52 a-f
17.53 b-e
UPLB SP 6
98.00 e
107.33 e
102.67e
17.03 b-g 17.10 b-g
17.07 c-h
UPLB SP 10
88.00 h
94.00 i 91.00i
18.55 a-d 18.97
a-d
18.76 abc
UPLB SP 12
65.00 r
76.67 p
70.83op
17.28 a-g 17.41
a-f
17.35 b-f
UPLB SP 24
75.67 n
79.00 o 77.33m
15.85 e-k 16.24
e-h
16.04 e-I
L- Mean
83.26b
91.16 a
87.21
16.34b
16.84a
16.59
CV(%) =1.7
*Means with the same letters are not significantly different at 5 % level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
48
Figure 2. Number of stomates on the abaxial leaf surface of representative sweetpotato
genotypes as affected by water stress level.
Interaction effect. There was a significant interaction between the
genotypes and level of water stress on the number of stomates on the abaxial
portion of the leaves. Genotype JK 18-4 under moderate stress had the highest
number of stomatescm2 -1 and the lowest number of stomate-1cm2 was observed
from UPLSP 3 under normal condition (Figure 2).
Number of Stomates on the Adaxial Portion of Leaves
Effect of genotype. Significant differences on the number of stomates on
the adaxial portion of the leaves were noted. Genotype UPLB-SP 4 had the most
number of stomates cm2 -1 with a mean of 19.50 while the least number of
stomates- cm2 -1 was observed from genotype NSIC 31. Other genotypes had
stomates cm2 -1 ranging from 13.39 to 19.39 (Table 3). According to Gardener et
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
49
al., (1985) stomatal number and size are genotypic characters of plants and
have less effect on total transpiration than stomatal opening and closing. When
stomata open wider more water is lost especially under increased solar radiation,
high temperature and windy condition.
Effect of water stress level. Level of water stress significantly affected
the number of stomates on the adaxial portion of the leaves. Genotypes under
moderate stress (60 cb) registered a higher number of stomates cm2 -1 on the
adaxial portion of the leaves, and the genotypes under not stressed had lesser
number of stomates cm2 -1. Other genotypes had a number of stomates-1cm2
ranging from 3.36 to 19.29 (Table 3). According to Xu and Zhou (2008)
moderate water deficits had positive effects on stomatal number, but more severe
deficits led to a reduction. The stomatal size obviously decreased with water
deficit, and stomatal density was positively correlated with stomatal conductance
(gs), net CO2 assimilation rate (An), and water use efficiency (WUE).
Interaction effect. Genotypes and level of water stress significantly
affected the number of stomates on the adaxial portion of the sweetpotato leaves.
Genotype UPL-SP 4 under moderate stress (60 cb) had the highest number of
stomates cm2 -1 while the least number of stomates cm2 -1 was observed from
NSIC 31 under no stress (Figure 3).
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
50
Figure 3. Number of stomates on the abaxial leaf surface of the representative
sweetpotato genotypes as affected by water stress level.
Leaf
Characteristics
Most of the genotypes exhibited planophyle leaf orientation while
genotypes Japanese-Inube and JK 23 -1 had erectophyle leaf orientation.
Erectophyle leaf orientation was noted to be efficient in intercepting solar
radiation.
Most of the genotypes’ reaction to water deficit were shedding and
dropping. Genotypes UPLB SP 5, Taiwan N, JK 7-4 and JK 18-4 had dropping
leaves as a response to water deficit. This conforms with the study of Amthor
(2005) that dropping, shedding and curling are crop responses to high
temperature and limited irrigation to reduce transpiration.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
51
Leaf Area
Effect of genotype. Genotypes significantly different on their leaf area.
Genotype NSIC 28 had the largest leaves followed by Taiwan D while the
smallest leaves were noted from genotype Super Bureau B. Other genotypes had
leaf size ranging from 19.24 to 94.95 cm2 (Table 4). The large leaf of NSIC 28
could be a mechanism to endure drought stress. According to Del Ocampo (2002)
the capacity to form leaves and sensitivity of leaf development in response to
water stress were apparently under genetic control.
Effect of water stress level. Significant effect of level of water stress was
noted on the area per leaf at 35 days after planting (DAP). Leaf area of the
genotypes under normal condition were higher than under moderate stress (60 cb).
This could be attributed to the effect of water stress on leaf expansion. Insufficient
water supply inhibits cell division and expansion resulting in the production of
smaller leaves (ICPRE and UI-CALS, 2002; Pritchard and Amthor, 2005).
Quisenberry (1982) found that the reduced leaf area observed in the stressed
plants resulted primarily from a mitotic sensitivity to water stress.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
52
Table 4. Leaf area of the 40 sweetpotato genotypes as affected by water stress
level
LEAF AREA (cm2)
WATER STRESS LEVEL
GENOTYPE NO
MODERATE
STRESS
STRESS
G- MEAN
(20 cb)
(60 cb)
BSU # 1
75.70 d 20.19
p-s
47.95 f
Bureau – N
35.96 jk
42.27 h
39.11 gh
Haponita
63.09 f 86.42
c
74.76 c
Inubi –BS
29.65 lmo 30.28
i-m 29.97
j
Inubi – Ca
18.93 pq
23.97 n-r 21.45
m
Inubi- N
26.50 mno 20.19
p-s
23.34 m
Japanese Inubi
22.71 op
25.23 m-p
23.97 kl
JO6-30-3
26.50 mno
24.60 m-q 25.55
k
JOG- 11-10
30.28 lmo
34.07 i 32.18 I
JO6-11-22
35.96 jk
18.30 rs
27.13 k
JK -7-4
30.28 lmn 26.50
l-o 28.39
jk
JK-18-4
68.13 e
56.78 f
62.46 d
JK- 23-1
34.07 jkl
92.74 b
63.40 d
MBE –SP
26.50 mno 23.97
n-r
25.24 kl
NSIC 23
47.32 hg
32.17 i-l 39.75
g
NSIC 24
23.34 op
15.14 s 19.24
n
NSIC 28
140.68 a
88.95 bc 114.28
a
NSIC 29
30.28 lmn
15.14 s 22.71
m
NSIC 31
37.85 ij
32.80 ijk 35.33
h
NSIC -31 BSU
22.71 op 19.56
p-s
21.13 mn
SG-02-06-02
81.38 c
54.26 fg
67.82 d
SG-02-13-02
27.76 mno
20.19 p-s
23.97 klm
SG-02-05-01
32.17 klm
66.24 e
49.21 f
SG-98-6-02
84.54 bc
19.56 p-s
52.05 e
SG-02-07-05
34.07 jkl 27.76
j-o
30.91 ij
SG-03-39-01
60.56 f
18.93 qrs
39.75 g
SP-30-03
25.23 no
20.19 p-s
22.71 m
Super bureau B
17.33 q
18.93 qrs
18.13 n
Super Bureau –N
51.10 g
49.84 g
50.47 ef
Taiwan- D
88.32 b
101.57 a
94.95 b
Taiwan- R
28.39 l-o 29.65
i-n
29.02 j
UPLB SP 1
36.59 jk
33.44 ij 35.01
hi
UPLB SP 2
42.27 hi 30.28
i-m 36.27
h
UPLB SP 3
47.35 gh 26.50
l-o
36.92 h
UPLB SP 4
48.58 g 26.50
h
44.16 fg
UPLB SP 5
34.07 jkl 30.28
i-m 32.17
i
UPLB SP 6
28.39 1mno 28.39
i-o 28.39
j
UPLB SP 10
80.12 cd
73.74 d 76.93
c
UPLB SP 12
39.74 ij
27.13 k-o 33.44
hi
UPLB SP 24
38.48 ij
23.34 o-r
30.91 ij
L-Mean
43.82 a 36.73
b
CV(%)= 7.8
*Means with the same letters are not significantly different at 5 % level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
53
Figure 4. Leaf area (cm2) as affected by the interaction of sweetpotato
genotypes and water stress level
Interaction
effect. Leaf area was significantly affected by the interaction
of genotypes and level of water stress (Figure 4). Genotypes under moderate
stress condition (60 cb) had smaller leaves than the leaves of the genotypes not
stressed (20 cb). Water stress during vegetative stage inhibits both cell expansion
and division leading to reduced leaf area resulting to the production of smaller
leaves, reduce vine and root expansion, plant height, and delays canopy
development but tends to acclimate the plant to water stress (IICPRE and UI-
CALS, 2002).
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
54
Root
Length
Effect of genotype. Root length of genotypes significantly different
among the genotypes (Table 5.) Genotype JK 23-1 significantly produced the
longest roots but comparable with NSIC 23 followed by Inubi – CA. While the
shortest roots were noted from genotype NSIC 28. Root length ranged from 4.93
cm to 9.37 cm. Longest roots of the genotypes may be a mechanism to endure
water stress.
Effect of water stress level. Length of roots at harvest was significantly
affected by the level of water stress (Table 7.) Longer roots were observed from
genotypes under normal condition than genotypes under moderate stress condition
(60 cb). Trachsel et al., (2011) found that plants exposed to water stress led to
the reduction in elongation rates of lateral roots. Nejad (2011) likewise stressed
that root length, number, weight and volume decreased quite in a mild drought
stress.
Interaction
effect. Genotypes and level of water stress significantly
interacted to affect the length of roots (Figure 5). The longest roots were observed
from genotype NSIC 23 under normal condition (20 cb) while the shortest roots
were observed from genotype Inubi B under moderate stress condition (60 cb)
Thangadurai et.al., (2007) cited that many plant species are able to increase water
uptake efficiency by developing deep and extensive root system under period of
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
55
Table 5. Length of roots of the 40 sweetpotato genotypes as affected by water
stress level
ROOT LENGTH (cm)
WATER STRESS LEVEL
GENOTYPE
NO STRESS
MODERATE
G-MEAN
(20 cb)
STRESS (60 cb)
BSU # 1
8.87 de
7.86 def
8.37 b
Haponita
6.73 lmn
5.66 mn
6.20 d
Inubi –BS
5.67 o 4.19
q
4.93 f
Inubi – Ca
9.63 bc
8.18 cde
8.91 b
Inubi- N
7.33 jk
6.29 k
6.81 d
Japanese Inubi
7.23 jkl
4.82 p
6.03 e
JK -7-4
9.47 bc
7.34 gh
8.40 b
JK-18-4
9.37 cd 7.97
cde 8.67
b
JK- 23-1
11.63 a
10.27 a
10.95 a
JO6-30-3
6.63 n
5.24 m-p
5.94 e
JOG- 11-10
9.75 bc
8.28 cde
9.02 b
JOG-11-22
7.73 h-k
6.19 kl
6.96 d
MBE –SP
9.23 cde
8.30 bcd
8.81 b
NSIC 23
9.92 b
8.81 b
9.37 ab
NSIC 24
6.70 lmn
5.35 m-p
6.02 e
NSIC 28
5.47 o
4.30 q
4.88 f
NSIC 29
6.60 n
5.35 m-p
5.97 e
NSIC 31
9.77 bc
7.44 fgh 8.61
b
NSIC -31 BSU
6.65 n
5.14 nop
5.89 e
SG-02-06-02
6.60 lmn
5.24 m-p
5.97 e
SG-02-13-02
5.73 o
5.03 op
5.38 ef
SG-02-05-01
7.20 klm 6.29
k
6.75 d
SG-98-6-02
8.20 ghi
5.24 m-p
6.72 d
SG-02-07-05
8.37 fg
7.76 efg
8.06 bc
SG-03-39-01
7.70 ijk 6.50
jk
7.10 cd
SP-30-03
6.70 lmn 6.19
kl
6.44 d
Super bureau B
6.77 lmn
5.35 m-p
6.06 de
Super Bureau –N
6.67 mn
5.35 m-p
6.01 e
Taiwan- D
6.63 n
5.24 m-p
5.94 e
Taiwan – N
8.77 ef
7.34 gh
8.05 bc
Taiwan- R
6.73 lmn 5.56
mno
6.15 d
UPLB SP 1
7.77 hij 6.39
k
7.08 cd
UPLB SP 2
6.67 mn
5.77 lm
6.22 d
UPLB SP 3
8.00 ghi
7.34 gh
7.67 c
UPLB SP 4
8.33 fg
6.81 ij
7.57 c
UPLB SP 5
7.67 ijk 5.77
lm
6.72 d
UPLB SP 6
6.67 mn
5.35 m-p
6.01 e
UPLB SP 10
7.98 ghi
7.44 fgh
7.71 c
UPLB SP 12
8.94 de
8.49 bc
8.71 b
UPLB SP 24
8.25 fgh
7.02 hi
7.64 c
L- Mean
7.77 a
6.46 b
7.12
CV(%)= 4.2
*Means with the same letters are not significantly different at 5 % level by DMRT
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
56
Figure 5. Root length of 10 representative sweetpotato genotypes as affected
by water stress level
drought. The degree of deep rooting can be a function of the plants root
penetration ability due to the mechanical impedance of various soil types and root
morphological characteristic such as length and density.
Number of Roots
Effect of genotype. Number of roots significantly varied among the
different genotypes (Table 6). Genotype MBE- SP produced the highest number
of roots while the lowest number of roots was observed from Inubi- BS and
SG-02-06-02. Other genotypes had number of roots ranging from 5.50 to 12.00.
Effect of water stress level. Number of roots was greatly affected by level
of water stress (Table 6). Genotypes not stressed produced higher number of
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
57
roots with while the lower number of roots was observed genotypes under
moderate stress condition. Root length density decreased with decreasing soil
moisture and increasing soil mechanical impedance (Thangaraj, 1990). Nejad
(2011) found that increased water stress reduced the root weight of the plants.
Interaction
effect. Number of roots was significantly affected by the
interaction of genotypes and level of water stress (Figure 7). Generally, genotypes
under normal condition produced more number of roots except for genotypes
Taiwan –D, JK 7-4, MBE-SP and Inubi – CA which produced higher number of
roots under moderate stress condition (60 cb). Water stress sometimes stimulates
roots growth and this presumably represents a mechanism to compensate for
limited water supply (Pritchard and Amthor, 2005).
Genotypes Inubi- BS, Super Bureau N and SG-02-06-02 under moderate
stress condition produced the lowest number of roots with a mean of 4.0 cm.
Dami (1995) found in grapes that there was a reduction and slow production of
roots under water stress.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
58
Table 6. Number of roots of the 40 sweetpotato genotypes as affected by water
stress level
NUMBER OF ROOTS
WATER STRESS LEVEL
GENOTYPE
NO STRESS
MODERATE STRESS
(20 cb)
(60 cb)
G- MEAN
BSU # 1
12.00 a
19.67bcd
11.33 b
Haponita
8.00 de
7.00 gh
7.50 ef
Inubi –BS
5.00 g 4.00
j
4.50 h
Inubi – Ca
10.00bc 11.00 bc
10.50 b
Inubi- N
9.00 cd 8.00
efg
8.50 de
Japanese Inubi
7.00 ef
7.00 gh
7.00 f
JK -7-4
7.00 ef
9.00 def
8.00 e
JK-18-4
12.00 a
12.00 b
12.00 b
JK- 23-1
9.00 cd
8.00 efg
8.50 de
JO6-30-3
7.00 ef
6.00 hi
6.50 f
JOG- 11-10
11.00 ab 10.00
cd
10.50 b
JOG-11-22
6.00 gf 5.00
ij
5.50 g
MBE –SP
11.00 ab
17.00 a
14.00 a
NSIC 23
9.00 cd 9.00
def 9.00
d
NSIC 24
7.00 ef
6.00 hi
6.50 fg
NSIC 28
8.00 de
8.00 efg
8.00 e
NSIC 29
10.33 abc
7.00 gh 8.67
d
NSIC 31
11.00 ab
10.00 cd 10.50b
NSIC -31 BSU
10.00 bc 9.00
def
9.50 cd
SG-02-06-02
5.00 g 4.00
j 4.50
h
SG-02-13-02
6.00fg
5.00 ij
5.50 g
SG-02-05-01
5.00 g
4.00 j
4.50 h
SG-98-6-02
6.00 fg 5.00
ij
5.50 g
SG-02-07-05
10.00 bc
9.00 def
9.50 c
SG-03-39-01
8.00 de 7.00
gh 7.50
ef
SP-30-03
9.00 cd
8.00 efg 8.50
de
Super bureau B
7.00 ef
7.00 gh
7.00 f
Super Bureau –N
7.00 ef
4.00 j 5.50
g
Taiwan- D
6.00 fg
7.33 fgh 6.67
f
Taiwan – N
12.00 a
11.00 bc
11.50 b
Taiwan- R
8.00 de
7.00 gh 7.50
ef
UPLB SP 1
8.00 de
8.00 efg
8.00 d
UPLB SP 2
7.00 ef
6.00 hi
6.50 f
UPLB SP 3
9.00 cd
9.00 def
9.00 c
UPLB SP 4
10.00 bc 9.67
cde
9.83 c
UPLB SP 5
9.00 cd 9.00
def
9.00 c
UPLB SP 6
7.00 ef
7.00 gh
7.00 c
UPLB SP 10
7.67 def 7.00
gh
7.33 ef
UPLB SP 12
9.00 cd 7.67
fgh 8.33
de
UPLB SP 24
9.00 cd
9.00 def
9.00 d
L- Mean
8.35 a 7.86
b
CV(%)= 12.6
*Means with the same letters are not significantly different at 5 % level by DMRT
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
59
Figure 6. Number of roots as affected by the interaction of genotypes and water
stress level
Length of Shoots Before and After Water Stress Imposition
Effect of genotype. Results show significant differences among the
different genotypes on the length of shoots (Table 7). All genotypes exhibited
increased in shoot length except for Super Bureau N. The longest shoots before
imposing stress were observed from genotype JK18- 4 and shortest shoots were
obtained from Super Bureau B.
The longest shoots after stress imposition were observed from genotype
UPLB SP 2 and the shortest shoots were measured from genotype Taiwan D.
Reduced shoot growth could be a mechanism of crops to endure water stress.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
60
Table 7. Shoot length before and after exposing to drought of the 40 sweetpotato
genotypes as by affected by water stress level
SHOOTS LENGTH (cm)
LEVEL OF WATER STRESS
NO STRESS
MODERATE
GENOTYPE
(20 cb)
STRESS (60 cb)
BEFORE
AFTER
INCREMENT
BEFORE
AFTER
INCREMENT
BSU # 1
18.87 b
21.43 d
2.56
16.83 d 19.10
cd 2.27
Haponita
15.28 h
18.14 gh
2.86
15.22 g 16.46
h 1.24
Inubi –BS
14.11 jk 17.40
I
3.29
14.05 I 15.29
klm 1.24
Inubi – Ca
15.20 h
16.80 j
1.60
13.11 lm 14.09
opq 0.98
Inubi- N
11.78 q
12.56 pq
0.78
8.87 t 11.97
st 3.10
Japanese Inubi
14.27 jk
17.53 hi
3.26
12.69 n 14.17
opq 1.48
JK -7-4
11.69 q
14.33 n
2.64
19.49 b 19.59
d 0.10
JK-18-4
20.47 a
23.29 b
2.82
18.03 c 19.92
b 1.89
JK- 23-1
14.28 jk
15.82 kl
1.54
13.00 m 13.89
pqr 0.89
JO6-30-3
15.03 h
18.16 gh
3.13
13.31 kl 16.17
hi 3.40
JOG- 11-10
14.38 j
17.96 ghi
3.58
12.10 o 15.57
i-m 3.47
JOG-11-22
15.59 g
18.44 fg
2.85
14.47 h 15.84
ijk 1.37
MBE –SP
18.03 c 19.67
e
1.64
16.74 de 17.81
f 1.07
NSIC 23
13.98 k
15.35 lm
1.37
13.58 jk 15.96
hij 2.38
NSIC 24
9.24 v
14.10 n
4.86
8.67 tu 9.66
v 0.99
NSIC 28
16.10 f
18.95 f
2.85
13.35 kl 15.55
i-m 2.20
NSIC 29
11.06 r
15.01 m
3.95
10.71 r 12.42
s 1.71
NSIC -31 BSU
14.75 I
17.92 ghi 3.17 16.33
f 18.71
de 2.38
NSIC 31
12.56 o 16.14
k
3.58
11.13 q 15.52
j-m 4.39
SG-02-06-02
12.37 no
12.81 qr
0.44
12.13 o 12.56
s 0.43
SG-02-13-02
12.87 n
13.03 op
0.16
12.58 n 13.73
qr 1.15
SG-02-05-01
13.00 mn 15.73
kl
2.73
14.83 ij 16.06
hij 1.23
SG-98-6-02 11.93
pq
13.08 op
1.15
11.04 q 13.40
r 2.36
SG-02-07-05
18.88 b
22.12 c
3.24
14.55 h 15.80
i-l 1.25
SG-03-39-01
13.19 lm 15.94
k
2.75
10.34 s 14.30
opq 3.96
SP-30-03
14.71 I
18.52 fg 3.81 15.23
g 17.29
fg 2.06
Super bureau B
6.23 x
14.03 n
7.80
8.45 u 10.79
u 2.34
Super Bureau –N
14.22 jk
16.11 k
1.89
11.78 p 14.46
nop 2.68
Taiwan D
8.72 w
11.94 r
3.22
6.17 v 6.64
w 0.27
Taiwan- N
13.42 l
16.03 k
2.61
12.05 op 15.03
mn 2.98
Taiwan- R
10.20 t
12.64 pq 2.44 10.34
s 12.04
st 1.70
UPLB SP 1
12.08 p 16.77
j
4.69
15.05 g 18.51
e 3.46
UPLB SP 2
10.08 t
24.82 a
14.12
20.36 a 21.95
a 1.59
UPLB SP 3
16.89 e
18.91 f
2.02
12.62 n 14.43
nop 1.81
UPLB SP 4
17.69 d
17.89 ghi
0.20
16.54 ef 15.48
j-m 1.06
UPLB SP 5
14.15 jk
18.34 fg
4.19
13.18 lm 17.06
g 3.88
UPLB SP 6
15.82 g
17.88 ghi
2.06
16.95 d 19.60
bc 2.65
UPLB SP 10
15.70 g
16.73 j
1.03
11.23 q 14.24
opq 3.01
UPLB SP 12
10.52 s
13.45 o
2.93
12.43 n 15.18
lm 2.75
UPLB SP 24
9.76 u
11.13 s
1.37
11.21 q 14.52
nop 3.31
L- Mean
13.74 a
16.66 a
2.92
13.24 b 15.12
b 1.88
CV(%)=
1.2
CV(%)
=2.1
*Means with the same letters are not significantly different at 5 % level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
61
Dami (1995) found that tobacco plantlets treated with PEG showed reduction in
shoot growth and lack of roots.
The highest increment in shoot length was observed from genotype NSIC
24 while the lowest increment was observed from UPLSP 3. High shoot length
increment means that genotypes may have the ability to grow faster even under
water deficit condition.
Effect of water stress level. Shoot length was significantly affected by
water stress level. The longest shoots after stress imposition were observed from
genotypes under normal condition while the shortest shoots were observed from
genotypes under moderate stress. According to Fernandez et al., (1997) there was
a consistent shoot length reduction due to drought stress.
Interaction effect. After stress imposition, shoot length significantly
different among genotypes at different water stress level (Figure 8). Genotypes
UPLB –SP 2 and JK18-4 under normal condition exhibited the longest shoots.
Shortest shoots were observed from genotype Taiwan D under moderate stress
(60 cb). This conforms with the findings of Kirnak et al. (2001) in eggplants
showing that water stress reduced both stem height and internode diameter by
46% to 51% under 40 % field capacity.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
62
Figure 7. Shoot length before water stress imposition of representative sweetpotato
genotypes as affected by water stress level.
Figure 8. Shoot length after water stress imposition of ten best genotypes as
affected by water stress level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
63
Physiological Parameters
Drought
Score
Effect of genotype. Drought score significantly differed among the
genotypes (Table 10). Lowest drought were observed in genotypes NSIC 23,
NSIC 31, Taiwan D, JOG 11-10, JK7-4, JK17-4, JK 23-1, BSU #1, MBE –SP and
Inubi- CA. Low drought score means there was no stress observed or all the
leaves were turgid in all the plants observed. This might be due to the long roots
of these genotypes which can absorb more water under limited water supply and
wide leaves to conserve moisture by covering the soil to minimize soil
evaporation.
Effect of water stress level. Significant differences in drought score as
affected by level of water stress were observed (Table 8). Lower drought score
was observed from the unstressed plants. Low drought score could be attributed
to the acculable water on a saturated soil (20 cb).
Interaction
effect. Genotypes and level of water stress interacted
significantly to affect drought score. Genotypes NSIC 23, NSIC 31, Super
Bureau N, JOG 11-10, JK 7- 4, JK-18- 4 ,JK 23-1, BSU #1, MBE –SP and
Inubi–CA subjected to moderate stress (60 cb) had the lowest drought score.
This could be attributed to the characteristic of Super Bureau B of producing roots
slowly. Salim (2010) found that shoot/root ratios consistently decrease under
drought stress, which is a universal expression of adaptation.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
64
Table 8. Drought score of the 40 sweetpotato genotypes as affected by water
stress level
DROUGHT
SCORE*
WATER STRESS LEVEL
GENOTYPE
NO STRESS
MODERATE
G-MEAN
(20 cb)
STRESS (60 cb)
BSU # 1
1.00 a
1.00 f
1.00 fg
Haponita
1.00 a
2.99 d
1.99 d
Inubi –BS
1.00 a
4.99 c
3.00 bc
Inubi – Ca
1.00 a
1.00 f
1.00 fg
Inubi- N
1.00 a
2.99 d 1.99
d
Japanese Inubi
1.00 a
2.99 d 1.99
d
JK -7-4
1.00 a 1.00
f
1.00 g
JK-18-4
1.00 a
1.00 f
1.00 g
JK- 23-1
1.00 a
1.00 f
1.00 g
JOG-30-3
1.00 a
2.99 d 1.99
d
JOG- 11-10
1.00 a
1.00 f
1.00 g
JOG-11-22
1.00 a
4.99 c
2.99 c
MBE –SP
1.00 a
1.00 f
1.00 g
NSIC 23
1.00 a
1.00 f 1.00
g
NSIC 24
1.00 a
4.99 c 2.99
c
NSIC 28
1.00 a
2.99 d 1.99
d
NSIC 29
1.00 a
4.99 c 2.99
c
NSIC 31
1.00 a
1.00 f 1.00
g
NSIC -31 BSU
1.00 a
2.99 d
1.99 d
SG-02-06-02
1.00 a 2.99
d 1.99
d
SG-02-13-02
1.00 a
2.99 d
1.99 d
SG-02-05-01
1.00 a
2.99 d
1.99 d
SG-98-6-02
1.00 a
2.99 d 1.99 d
SG-02-07-05
1.00 a
2.99 d
1.99 d
SG-03-39-01
1.00 a
2.99 d
1.99 d
SP-30-03
1.00 a
4.99 c
2.99 c
Super bureau B
1.00 a
8.99 a 4.99
ab
Super Bureau –N
1.00 a
4.99 c 2.99
c
Taiwan- D
1.00 a
1.00 f 1.00
g
Taiwan –N
1.00 a
1.67 e 1.33
e
Taiwan- R
1.00 a 8.99
a
5.00 a
UPLB SP 1
1.00 a
6.99 b
3.99 b
UPLB SP 2
1.00 a
2.99 d 1.99
d
UPLB SP 3
1.00 a
2.99 d
1.99 d
UPLB SP 4
1.00 a
2.99 d 1.99
d
UPLB SP 5
1.00 a
2.99 d
1.99 d
UPLB SP 6
1.00 a
2.99 d
1.99 d
UPLB SP 10
1.00 a
6.99 d 3.99
b
UPLB SP 12
1.00 a
2.99 d 1.99
d
UPLB SP 24
1.00 a
4.99 c 2.99
c
L-Mean
1.00 b
3.30 a
2.15
*Rating scale: 1- no stress; 2 – 30% of the leaves wilted; 5- 50% of the leaves wilted; 7- 80% of the leaves
wilted; 9- complete wilting and death of plants.
CV(%)= 15.0
*Means with the same letters are not significantly different at 5 % level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
65
Recovery
Rating
Effect of genotype. Significant differences on the recovery rating of the
different genotypes is shown in Table 9. Generally, the different genotypes had a
complete recovery. Complete recovery from water stress may imply degrees of
resistance of the genotypes evaluated.
Effect of water stress level. Recovery rating of the plants was not affected
by water stress level. All plants recovered after 24 hr of irrigation.
Interaction effect. Genotypes and level of stress did not affect the
recovery rating although all genotypes subjected to moderate stress (60 cb) had
lower recovery rating.
Relative Water Content (RWC)
Effect
genotype. Significant difference were observed on the relative
water content of the different genotypes (Table 10). Highest RWC was recorded
from JK 23-1 but comparable with Haponita. The lowest RWC was obtained
from NSIC 28. This could be attributed to the characteristic of the leaves to
absorb more water than other genotypes. Plants were able to regain turgidity to
certain extent Laurel et al., (2009).
Effect of water stress level. Relative water content (RWC) of plants at
35 DAP was significantly affected by the level of water stress. Plants under
normal condition had lower RWC while and higher RWC was observed from
plants under moderate stress (60 cb).
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
66
Table 9. Recovery rating of the 40 sweetpotato genotypes as affected by water
stress level
RECOVERY RATING *
WATER STRESS LEVEL
GENOTYPE
NO STRESS
MODERATE
G-MEAN
(20 cb)
STRESS (60 cb)
BSU # 1
9.00 a
8.99 a 8.99
a
Haponita
9.00 a
8.99 a
8.99 a
Inubi –BS
9.00 a
8.99 a 8.99
a
Inubi – Ca
9.00 a
8.99 a
8.99 a
Inubi- N
9.00 a
8.99 a 8.99
a
Japanese Inubi
9.00 a
8.99 a
8.99 a
JK -7-4
9.00 a 8.99
a 8.99
a
JK-18-4
9.00 a
8.99 a
8.99 a
JK- 23-1
9.00 a
8.99 a 8.99
a
JO6-30-3
9.00 a
8.99 a
8.99 a
JOG- 11-10
9.00 a
8.99 a 8.99
a
JOG-11-22
9.00 a
8.99 a
8.99 a
MBE –SP
9.00 a
8.99 a 8.99
a
NSIC 23
9.00 a
8.99 a
8.99 a
NSIC 24
9.00 a 8.99
a 8.99
a
NSIC 28
9.00 a
8.99 a
8.99 a
NSIC 29
9.00 a
8.99 a 8.99
a
NSIC 31
9.00 a
8.99 a
8.99 a
NSIC -31 BSU
9.00 a
8.99 a 8.99
a
SG-02-06-02
9.00 a
8.99 a
8.99 a
SG-02-13-02
9.00 a
8.99 a 8.99
a
SG-02-05-01
9.00 a
8.99 a
8.99 a
SG-98-6-02
9.00 a 8.99
a 8.99
a
SG-02-07-05
9.00 a
8.99 a
8.99 a
SG-03-39-01
9.00 a
8.99 a
8.99 a
SP-30-03
9.00 a
8.99 a 8.99
a
Super bureau B
9.00 a
0.99 d 5.00c
Super Bureau –N
9.00 a
2.96 c 5.98bc
Taiwan- D
9.00 a
8.99 a 8.99
a
Taiwan –N
9.00 a
8.99 a 8.99
a
Taiwan- R
9.00 a 8.99
a
8.99 a
UPLB SP 1
9.00 a
8.99 a 8.99
a
UPLB SP 2
9.00 a
8.99 a
8.99 a
UPLB SP 3
9.00 a
8.99 a 8.99
a
UPLB SP 4
9.00 a
8.99 a
8.99 a
UPLB SP 5
9.00 a
8.99 a 8.99
a
UPLB SP 6
9.00 a
8.99 a
8.99 a
UPLB SP 10
9.00 a
8.32 b 8.66ab
UPLB SP 12
9.00 a 8.99
a 8.99
a
UPLB SP 24
9.00 a
8.99 a
8.99 a
L-Mean
9.00 a
8.62b
8.81
*Recovery rating : 1 – no recovery; 3- 30% of the leaves recovered ; 5 – 50% of the leaves recovered ;
7 – 80% of the leaves recovered; 9- complete recovery of the plants.
CV(%) = 1.5
Means with the same letters are not significantly different at 5 % level by DMRT
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
67
Table 10. Relative water content of the 40 sweetpotato genotypes as affected by
water stress level
RELATIVE WATER CONTENT (%)
LEVEL OF WATER STRESS
GENOTYPE NO
STRESS
MODERATE
G-MEAN
(20 cb )
STRESS (60 cb)
BSU # 1
27.66 c-i 33.96
bf 30.81 bc
Haponita
42.68 a
44.12 a 43.40 a
Inubi –BS
31.10 bcd 36.42
bc 33.76 b
Inubi – Ca
29.42 b-f
27.43 gh
28.42 cd
Inubi- N
22.76 i-n
22.82 hij 22.79 de
Japanese Inubi
28.03 b-h 31.17
d-g 29.60 cd
JK -7-4
29.97 b-e
30.55 d-g
30.26 bc
JK-18-4
27.92 b-h
28.92 fg 28.42 cd
JK- 23-1
44.31 a 43.73
a 44.02 a
JO6-30-3
25.54 e-k
33.27 c-f 29.40 cd
JOG- 11-10
32.74 bc 29.19
fg 30.97 bc
JOG-11-22
32.85 b 38.32
b 35.59 b
MBE –SP
31.03 bcd
31.48 c-g
31.25 bc
NSIC 23
20.07 l-o
20.68 ij
20.38 de
NSIC 24
20.19 l-o 20.29
ij
20.24 e
NSIC 28
19.70 mno 15.59
k 17.65 e
NSIC 29
15.87 o 23.42
hij 19.65 e
NSIC 31
31.89 bcd
32.35 c-g 32.12 b
NSIC -31 BSU
28.97 b-g 30.29
d-g 29.63 cd
SG-02-06-02
28.76 b-g
32.65 c-f
30.70 bc
SG-02-13-02
25.70 e-k
29.89 efg 27.77 cd
SG-02-05-01
27.13 d-j
32.34 c-g 29.74 cd
SG-98-6-02
25.01 e-l 29.76
efg 27.39 cd
SG-02-07-05
24.55 f-m 35.10
bcd
29.83 c
SG-03-39-01
23.84 g-n
29.14 fg
26.49 cd
SP-30-03
28.04 b-h
32.26 c-g
30.15 bc
Super bureau B
24.21 g-n
24.46 hi
24.34 d
Super Bureau –N
22.06 j-n
22.59 hij 22.33 de
Taiwan- D
28.17 b-g 29.60
efg 28.88 cd
Taiwan – N
22.54 i-n
44.61 a 33.58 b
Taiwan- R
25.65 e-k 34.45
b-e
30.05 bc
UPLB SP 1
20.35 l-o 21.74
ij 21.05de
UPLB SP 2
19.83 l-o 20.32
ij
20.08e
UPLB SP 3
21.51 k-n
21.60 ij 21.55de
UPLB SP 4
21.41 k-n 23.29
hij 22.35 de
UPLB SP 5
19.19 no 19.21
jk 19.20 e
UPLB SP 6
19.92 l-o 20.70
ij
20.31 e
UPLB SP 10
22.95 h-n
23.14 hij 23.04 de
UPLB SP 12
22.56 i-n
23.17 hij 22.86 de
UPLB SP 24
22.96 h-n
23.13 hij 23.05 de
L- Mean
25.98 b 28.68 a
CV(%) =9.6
*Means with same letters in column are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
68
Interaction
effect. Significant interaction of genotypes and level of water
stress was observed on RWC at 35 DAP (Figure 10). Genotype Super Bureau N
subjected to moderate stress had the highest RWC while the lowest RWC was
observed from NSIC 28 subjected to moderate stress. Other treatment
combinations had RWC ranging from 15.87 to 43.73%. This conforms with
the study of Rai (1989) on bush beans subjected to water deficit which showed a
significant reduction of RWC of the leaves.
Figure 9. Relative water of content (%) of representative sweetpotato
genotypes as affected by water stress level
Garg (2004) cited that genotypes under drought condition had significant
decreased in plant water potential, relative water content, rate of net photosynthesis,
contents of chlorophyll, starch, soluble protein, and nitrate reductase activity.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
69
Other Growth Parameters
Percentage
Survival
Effect of genotype. Genotypes significantly varied n their survival at 30
DAP. Out of the 40 genotypes 25 genotypes had almost 100% survival. The
lowest survival were observed from genotypes UPLB SP 10 and NSIC 24. Other
genotypes had survival percentage ranging from 91.67 to 98.33% (Table 11).
Effect of water stress level. Percent survival at 30 DAP was significantly
affected by the level of water stress. Higher survival percentage was observed
from plants under normal condition. This result conforms with the study of
Badiane et al., (2003) that inadequate water availability is crucial limitation to
crop growth and yield and thus, survival.
Interaction
effect. Genotypes and water stress level interacted
significantly on the survival percentage. All genotypes under both normal and
moderate stress (60 cb) the survival percentage ranging from 88.33 to 99.99%. It
was also observed that genotypes under moderate stress had comparable with
those genotypes not stressed.
Plant
Vigor
Effect of genotype. Plant vigor at 30 DAP of the genotypes did not differ.
All genotypes had robust stems and leaves with light to dark green in color.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
70
Table 11. Survival percentage of the 40 sweetpotato genotypes as affected by
water stress level
SURVIVAL
PERCENTAGE
(%)
WATER STRESS LEVEL
GENOTYPE
NO STRESS
MODERATE
G-MEAN
(20 cb)
STRESS (60 cb)
BSU # 1
99.99 a 99.99
a 99.99
a
Haponita
99.99 a 99.99
a 99.99
a
Inubi –BS
99.99 a 99.99
a 99.99
a
Inubi – Ca
99.99 a 99.99
a 99.99
a
Inubi- N
99.66 b 99.66
b 99.66
a
Japanese Inubi
99.99 a 96.67
c 98.33
b
JK -7-4
99.99 a 99.99
a 99.99
a
JK-18-4
99.99 a 99.99
a 99.99
a
JK- 23-1
99.66 b 99.66
b 99.66
a
JO6-30-3
99.99 a 99.99
a 99.99
a
JOG- 11-10
99.99 a 99.99
a 99.99
a
JOG-11-22
99.99 a 99.99
a 99.99
a
MBE –SP
99.99 a 99.99
a 99.99
a
NSIC 23
99.99 a 99.99
a 99.99
a
NSIC 24
89.99 e 86.67
f 88.33
d
NSIC 28
99.99 a 96.67
c 98.33
b
NSIC 29
96.67c 93.33
d 95.00
c
NSIC 31
99.99 a 96.97
c 98.33
b
NSIC -31 BSU
99.99 a 99.99
a 99.99
a
SG-02-06-02
99.99 a 99.99
a 99.99
a
SG-02-13-02
99.99 a 96.67
c 98.33
b
SG-02-05-01
99.99 a 99.99
a 99.99
a
SG-98-6-02
99.99 a 99.99
a 99.99
a
SG-02-07-05
99.99 a 99.99
a 99.99
a
SG-03-39-01
99.66 b 99.66
b 99.66
a
SP-30-03
99.99 a 99.99
a 99.99
a
Super bureau B
99.99 a 99.99
a 99.99
a
Super Bureau –N
99.99 a 99.99
a 99.99
a
Taiwan- D
99.99 a 99.99
a 99.99
a
Taiwan – N
96.67 c 93.33
d 95.00
c
Taiwan- R
99.99 a 99.99
a 99.99
a
UPLB SP 1
100.00a 100.00
a 100.00
a
UPLB SP 2
100.00a 96.67
c 98.33
b
UPLB SP 3
99.67 c 96.67
c 96.67
c
UPLB SP 4
96.67 c 93.33
d 95.00
c
UPLB SP 5
100.00 a 93.33
d 96.66
c
UPLB SP 6
99.99 a 96.97
c 98.33
b
UPLB SP 10
93.33 d 83.33
g 88.33
d
UPLB SP 12
93.33 d 90.00
e 91.67
b
UPLB SP 24
93.33 d 86.67
f 90.00
b
L-Mean
98.99 a
97.39 b
98.14
CV(%) = 0.2
*Means with same letters in column are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
71
Effect of water stress level. Plant vigor at 30 DAP was not significantly
affected by level of water stress. All plants were highly vigorous.
Interaction
effect. Plant vigor at 30 DAP was not significantly affected
by genotypes and level of water stress. All genotypes were highly vigorous.
Plant Height
Effect of genotype. Plant heights at 10 DAP were significantly different
among genotypes. Genotype JK 18-4 registered the tallest plants at 10 DAP,
while the shortest plants were observed from Taiwan R with a mean height of
5.09 cm and Super Bureau B at 20 DAP (Table 12). Other genotypes had plant
heights ranging from 5.15 to 17.00 cm.
Plant heights at 30, 40 and 50 DAP are shown in Table 13. The tallest
genotypes were observed from UPLB SP 2. Shortest plants were obtained from
Taiwan N.
Effect of water stress level. Plant heights at 10, 20, 30, 40 and 50 DAP
were significantly affected by the level of waters stress (Table 13). Plants under
normal condition produced taller plants respectively while at 30 DAP plants
under moderate stress registered the tallest plants.
Interaction effect. The interaction of genotypes and level of water stress
significantly affected the height of the plants at 10, 20, 30, 40 and 50 DAP
(Figures 11, 12, 13, 14 and 15). Genotype UPLB SP2 exposed to normal
condition registered the tallest heights.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
72
Table 12. Plant height at 10, 20, and 30 DAP of the 40 sweetpotato genotypes
as affected by level of water stress
PLANT HEIGHT (cm)
LEVEL OF WATER STRESS
GENOTYPE
NO STRESS (20 cb)
MODERATE STRESS (60 cb)
10 DAP
20 DAP
30 DAP
10 DAP
20 DAP
30 DAP
BSU # 1
9.43ab
17.96b
18.41c
8.42b-e 16.03d
18.29cd
Haponita
7.62 c-h
14.51fgh
15.51efg
7.63c-g 14.52e
15.96hij
Inubi –BS
7.01 e-k
13.35ij
14.95ghi
7.00d-k 13.32gh
14.71ln
Inubi – Ca
7.57 c-I
14.42fgh
13.43lm
6.57g-m 12.51i-l
13.54o-r
Inubi- N
5.87 j-o 11.18mn
10.78qr
4.42nop 8.41s
10.8u
Japanese Inubi
7.06 e-k 13.45ij
15.00ghi
6.36g-m 12.1j-m
13.64o-r
JK -7-4
5.84 j-o 11.12mn
12.28no
9.75ab 18.56b
16.31hi
JK-18-4
10.24 a 19.52a
19.97b
9.01abc 17.16c
19.23b
JK- 23-1
7.07e-k 13.47i-j
13.53klm
6.51g-m 12.39i-l
13.57o-s
JOG-30-3
7.51d-i 14.31fgh
14.52hij
6.64g-m 12.65h-k
15.15j-m
JOG- 11-10
7.03e-k 13.39ij
15.41e-h
6.06h-m 11.54mn
14.29mno
JOG-11-22
7.74c-h 14.72efg
15.81efg
7.20 d-j 13.71fg
15.34jkl
MBE –SP
9.01abc 17.14c
16.87d
8.39b-e 15.98d
17.47def
NSIC 23
6.99 e-k 13.31ij
13.18lm
6.76f-l 12.87hij
15.1j-m
NSIC 24
4.61 op 8.78qr
12.09no
4.26op 8.10s
9.27v
NSIC 28
8.04 b-f 15.31e
16.24der
6.7f-m 12.75h-k
14.78k-n
NSIC 29
5.57 k-p 10.63no
12.84mn
5.34l-o 10.17qr
11.77t
NSIC -31 BSU
7.34 e-j 13.9klm
15.39jkl
8.18c-f 15.58pqt
17.91n-r
NSIC 31
6.24 h-n
11.89ghi
13.8e-h
5.58k-o 10.62d
13.91cde
SG-02-06-02
6.42 g-n 12.45k
13.66i-m
6.23g-m 11.56mn
13.24p-s
SG-02-13-02
6.43 g-n
12.23kl
11.57opq
6.3g-m 12.00k-n
13.34o-s
SG-02-05-01
6.56 f-m
12.48k
13.49klm
6.93e-k 13.19ghi
15.28jkl
SG-98-6-02 5.94
j-o 11.31mn
11.18pq
5.51k-o 10.5pqr
12.64s
SG-02-07-05
9.44 ab 17.98b
18.99c
7.27d-j 13.85efg
15.23jkl
SG-03-39-01
6.54 f-n
12.46k
13.66j-m
5.2l-o 9.90qr
12.97rs
SP-30-03
7.34 e-j 14.02ghi
15.86efg
7.61c-h 14.5e
16.56ghi
Super bureau B
3.11 q 5.92s 12.00nop
4.23op 8.06s
9.99v
Super Bureau –N
7.11 e-k
13.52i
13.88jkl
5.89j-n 11.21nop
13.52o-s
Taiwan D
5.01 nop 9.52jk
10.88j-m
5.17gmno
9.86mno
11.51n-q
Taiwan- N
4.34 pq 8.3ij
10.22rs
3.07p 5.81s
6.42w
Taiwan- R
6.66 f-l 12.69pq
13.71qr
6.03i-m 11.43r
14.01tu
UPLB SP 1
6.04 i-o 11.5
lm
14.38ijk
7.53 d-i 14.33ef
17.27efg
UPLB SP 2
5.04 m-p 9.6p
21.26a
10.17a 19.37a
21.36a
UPLB SP 3
8.45 b-e 16.09d
16.27de
6.33g-m 12.05klm
13.78o-r
UPLB SP 4
8.84 a-d 16.84c
15.36e-h
7. 41d-j 15.95d
16.75fgh
UPLB SP 5
7.08 e-k 13.8hi
15.73efg
6.57g-m 12.51i-l
15.69ijk
UPLB SP 6
7.9 c-g 15.04ef
15.31fgh
8.49bcd 16.16d
18.64bc
UPLB SP 10
6.35 g-n 12.1kl
14.4ijk
5.61k-o 10.69opq
13.14qrs
UPLB SP 12
5.26 l-p 10.02op
9.82s
6.21g-m 11.82lmn
14.17nop
UPLB SP 24
5.2 l-p 9.3pq
9.51s
5.5k-o 10.67opq
13.32p-s
T- Mean
6.82 a
12.99 a 14.28b 6.60
b
12.61 b
14.50a
CV(%)=11.7
CV(%)= 3.5
CV(%) = 3.5
*Means with same letters in column are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
73
Table 13. Plant height at 40 and 50 DAP of the 40 sweetpotato genotypes as
affected by level of water stress
PLANT HEIGHT (cm)
LEVEL OF WATER STRESS
NO STRESS (20 cb)
MODERATE STRESS (60 cb)
GENOTYPE
40 DAP
50 DAP
40 DAP
50 DAP
BSU # 1
24.55c
19.91c
30.69b
21.53b
Haponita
20.69ef
16.74fgh
25.86e-h
17.53f-i
Inubi –BS
19.93f-i
15.49i-m
24.91hi
16.28ijk
Inubi – Ca
19.25hij
14.4mno
24.06ijk
15.07klm
Inubi- N
14.38pq
13.00p
17.97pq
15.19klm
Japanese Inubi
20.04f-i
14.68l-o
25.00ghi
15.71jkl
JK -7-4
16.39no
12.79p
20.49no
9.26p
JK-18-4
26.63b
20.75b
33.29b
21.91b
JK- 23-1
18.03klm
14.19no
22.53lm
14.81lm
JOG-30-3
19.36q-j
17.23def
24.2ij
19.31cde
JOG- 11-10
20.55efg
16.69f-i
25.69fgh
19.1cde
JOG-11-22
20.07f-i
16.38f-j
26.34ghi
17.17ghi
MBE –SP
22.49d
18.23cd
28.11d
19cde
NSIC 23
17.58lm
16.86fgh
21.97 lm
18.63def
NSIC 24
16.11no
10.13r
20.14o
10.99o
NSIC 28
21.66de
16.35f-j
27.07de
17.91e-h
NSIC 29
17.14mn
12.99p
21.43mn
14.2mn
NSIC -31 BSU
18.4jkl
16.99efg
23.03jkl 20.06c
NSIC 31
20.53efg
19.66b
25.66fgh
21.39b
SG-02-06-02
17.88lm
13.89op
24.22ij
14.89lm
SG-02-13-02
15.43op
14.16no
17.29qr
14.98klm
SG-02-05-01
17.99klm
16.86fgh
22.49lm
18.45d-g
SG-98-6-02 14.89p
14.45mno
18.63p
16.26ijk
SG-02-07-05
25.33c 16.01f-k
31.66c
16.78hij
SG-03-39-01
18.22j-m
15.83g-l
22.77kl
18.7def
SP-30-03
21.14ef
18.06cde
26.43ef
19.55cd
Super bureau B
16.00o
11.68q
20.01o
13.37n
Super Bureau –N
18.49jkl
15.46i-m
23.11jkl
17.4f-i
Taiwan D
18.29j-m
16.19f-k
22.86jk
18.36d-g
Taiwan- N
13.52qr
6.78s
17.03qrs
7.14q
Taiwan- R
14.4pg
12.8p
18.00pq
14.09mn
UPLB SP 1
19.18ijk
19.77b
23.97ijk
22.26b
UPLB SP 2
28.34a
22.5a
35.43a
23.63a
UPLB SP 3
21.69de
15.03k-o
27.11de
16.28ijk
UPLB SP 4
20.48efg
16.75fgh
25.6fgh
16.75hij
UPLB SP 5
20.97e-f
18.51c
26.21e-h
21.34b
UPLB SP 6
20.41fgh
20.49b
25.56fgh
22.34b
UPLB SP 10
19.2ijk
15.29j-n
24.00ijk
17.41f-i
UPLB SP 12
13.1r
16.13f-k
16.37rs
18.09e-h
UPLB SP 24
12.69r
15.68h-l
15.86s
18.04e-h
Mean 19.03
a
23.83
a 17.28 b
CV(%)=3.7
CV(%)=
3.6
*Means with same letters in column are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
74
Figure 10. Plant height at 10 DAP of 10 sweetpotato genotypes as affected by
water stress level
Figure 11. Plant height at 20 DAP of 10 sweetpotato genotypes as affected by
water stress level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
75
Figure 12. Plant height at 30 DAP of 10 sweetpotato genotypes as affected by
water stress level
Figure 13. Plant height at 40 DAP of 10 sweetpotato genotypes as affected by
water stress level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
76
Figure 14. Plant height at 50 DAP of 10 sweetpotato genotypes as affected by
water stress level
Experiment 2. Evaluation of Selected Genotypes for Drought
Resistance under Greenhouse Condition
Meteorological Data
The greenhouse air temperature during the growing period ranged from
19 0C to 43 0C (Table 14). The highest temperature was observed in July
with 43 oC, while the lowest air temperature was observed in October with 18 oC.
The high temperature of 43 0C recorded was beyond the temperature
requirement of sweetpotato. According to Romero et al., (1991), sweetpotato
plants grow with temperatures between 15oC and 35oC and that lower and higher
temperatures have detrimental effects on yield. This condition may explain the
absence of storage roots of the genotypes evaluated in this study.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
77
Table 14. Greenhouse air temperature from June to September, 2011
GREENHOUSE AIR TEMPERATURE (0C)
MONTH
MINIMUM
MAXIMUM
MEAN
June 19
40 29.5
July
20
43
31.5
August
19
42
30.5
September
19
39
29.0
October
18
38
28.0
Mean
19
40.4
Morphological Parameters
Number of Stomates on the Abaxial Portion of Leaves
Effect of genotype. Significant differences among the genotypes existed
on the number of stomates on the abaxial portion of the leaves. Genotype JOG 11-
10 had the most number of stomata-1cm2 while the least was observed from
genotype NSIC 31. Other genotypes had stomates-1cm2 ranging from 87.22 to
122.44 (Table 15).
Effect of water stress level. The number of stomates on the abaxial
portion of leaves was significantly affected by the level of water stress (Table 15).
Genotypes under moderate stress condition (60 cb) showed the most number of
stomates-1cm2 in the abaxial portion of the leaves followed by genotypes under
severe stress condition (80 cb) and genotypes under control (20 cb) condition
Screening And Evaluation Of Sweet potato Genotypes
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78
registered the least number of stomata cm2 -1. The plant leaves lose water
primarily by transpiration through the stomata. The stomatal density depends
upon plant species, and can be related to the plant-ecotype between 300 and 800
stomata/mm (Rowland-Bamford et al., 1990). Furthermore, there was increased in
stomatal density of rice and bean leaves, with a differential effect at abaxial
(increasing) and adaxial sides. Moreover, many studies have shown that water
deficit leads to an increase in stomatal density (McCree and Davis, 1974; Cutler et
al., 1977; Yang and Wang, 2001; Zhang et al., 2006), and a decrease in stomatal
size (Cutler et al., 1977; Quarrie and Jones, 1977; Spence et al., 1986), indicating
that stomatal density may enhance the adaptation of plant to drought (Cutler et al.,
1977; Spence et al., 1986; Martinez et al., 2007).
Interaction effect. A significant interaction of genotypes and level of
water stress on the number of stomates cm2 -1 on the abaxial portion of the leaves
of sweetpotato existed (Figure 15). Genotype JOG 11-10 under moderate stress
(50 cb) registered the most number of stomates cm2 -1 on the abaxial portion of
the leaves while genotype JK 18-4 under control condition (20 cb) had the least
Other treatment combination had the number of stomates cm2 -1 ranging from
76.00 to 130.00. This confirms with results of Xu and Zhou (2008) on wheat that
moderate water deficits had positive effects on stomatal number, but more severe
deficits led to a reduction of stomata. Further, water stress decreases mean cell
size and reduces the number of stomata per leaf (Quarrie and Jones, 1977).
Screening And Evaluation Of Sweet potato Genotypes
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79
Table 15. Number of stomates on the abaxial leaf surface (cm2) of the 10
sweetpotato genotypes as affected level of water stress under
greenhouse condition
NUMBER OF STOMATES
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
(20 cb)
(60 cb)
(80 cb)
G-MEAN
BSU# 1
103.67 b 122.67
d
99.00 e
108.44 c
Inubi- CA
95.00 d 119.67
e 107.67
d 107.44
cd
JK-7-1 85.00
f 126.67
c 115.33
b 109.00
c
JK-18-4 74.00
h 124.67
cd 109.00
cd 102.56 d
JK 23-1
79.00 g 96.67
h 86.00
f 87.22
gh
JOG 11-10
99.00 c 175.00
a 111.00
c 128.33
a
MBE-SP 81.00
g 109.00
g 97.00 e 95.67
f
NSIC 23
91.33 e 111.67
f 97.00
e 100.00e
NSIC 31
76.00 h 98.00
h 82.00
g 85.33
g
TAIWAN- D
117.67 a 130.00
b 119.67 a 122.44
b
L- Mean
90.17 c
121.40 a
102.37 a
104.64
CV(%) = 1.3
*Means with the same letters in a column are no significantly different at 5%
level of DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
80
Figure 15. Number of stomates on the abaxial leaf surface (cm2) as affected by
the interaction of genotypes and level of water stress.
Number of Stomates on the Adaxial Portion of the Leaves
Effect of genotype. Significant differences among the genotypes on the
number of stomates in the adaxial portion of leaves were observed. Genotype
JOG 11-10 had the most number of stomatas cm2 -1 while the least was observed
from genotype NSIC 31. Other genotypes had stomates-1cm2 ranging from 13.83
to 19.44 (Table 16).
Effect of water stress level. Number of stomates on the adaxial portion
of leaves was significantly affected by the level of water stress. Genotypes under
moderate stress (60 cb) condition showed the highest number of stomates cm2 -1
on the adaxial portion of the leaves, followed by genotypes under severe stress
Screening And Evaluation Of Sweet potato Genotypes
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81
Table 16. Number of stomates on the adaxial leaf surface (cm2) of the 10
sweetpotato genotypes as affected level of water stress under
greenhouse condition
NUMBER
OF
STOMATES
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
(20 cb)
(60 cb)
(80 cb)
G-MEAN
BSU# 1
16.59 b 18.40
cd 16.83
d 7.27
b
JK-7-1 14.60
d 18.97
bc 19.26
ab 7.61b
JK-18-4 11.84
f 18.70
cd 18.20
c 6.25 c
JK 23-1
12.64 e 14.50
f 14.36
f 3.83
e
JOG 11-10
15.84 bc 26.25
a 18.54
bc 20.21 a
MBE-SP 13.29
e 16.35 e 15.75
e 5.13d
NSIC 23
14.61 d 16.75
e 16.20
de 5.85cd
NSIC 31
13.01 e 14.70
f 13.69
f 3.80
e
TAIWAN D
18.83 a 19.50
b 19.98
a 9.44
b
Inubi- CA
15.20 cd
17.95 d
17.98 c
7.04
bc
L-Mean
14.6c
18.21a
17.08b
CV(%)= 2.8
*Means with the same letters in a column are not significantly different at 5 %
level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
82
(80 cb) condition while genotypes under normal (20 cb) condition registered the
least number of stomates cm2 -1.
Interaction effect. There was a significant interaction of genotypes and
level of water stress on the number of stomates cm2 -1 on the adaxial portion of the
leaves of sweetpotato. Genotype JOG 11-10 under moderate stress (60 cb)
registered the most number of stomates cm2 -1 on the adaxial portion of the
leaves while genotype JK 18-4 under normal condition (20 cb) had the least.
Other treatment combinations had number of stomates cm2 -1 ranging from 12.64
to 19.98 (Figure 16). According to Klooster and Young (2004), the stomatal
density was 29 % higher in the dry vs. wet conditions which explains the higher
number of stomates during moderate and severe condition compared to the
unstressed condition.
Fig. 16. Number of stomates on the adaxial leaf surface (cm2) as affected by
genotypes and level of water stress
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
83
Leaf Characters
Leaf Orientation. Most of the genotypes exhibited planophyle leaf
orientation while genotype JK-23-1 had erectophyle leaf orientation. Erectophyle
leaf orientation was noted to be efficient in intercepting solar radiation.
Leaf Reaction to Moisture Deficit. Leaves of all genotypes responded to
water deficit through shedding and dropping. This conforms with the study of
Noogle and Fritz (1983) that drooping and sagging of plant tissues especially
leaves known as wilting which is due to change in elastic properties of cell walls
when turgor pressure declines below a certain critical value. The leaves of some
herbaceous plants sometimes droop and sag in the afternoon during hot weather
and recover again at night.
Physiological Parameters
Drought Score
Effect of genotype. Significant differences were observed on the
drought scores of the different genotypes (Table 17). Genotype Inubi –CA
registered the lowest drought score followed by genotypes Taiwan D, NSIC 31,
and BSU # 1 with 2.56 drought score. These genotypes have comparable drought
score with Inubi – CA. Low drought score may be attributed to mechanism that
help in absorbing sufficient water to maintain leaf turgidity during water stress
condition. One mechanism could be the production of pubescence in the leaves
which was exhibited by Inubi – CA.
Screening And Evaluation Of Sweet potato Genotypes
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Table 17. Drought score as affected by sweetpotato genotypes and level of
water stress under greenhouse condition
DROUGHT
SCORE*
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
MEAN
(20 cb)
(60 cb)
(80 cb
BSU# 1
1.00 a 2.33
cd 4.33
cd 2.56
bc
JK-7-1 1.67
a 4.33
b 8.33
a 4.78
ab
JK-18-4 1.67
a 6.33
a 8.33
a 5.44 a
JK 23-1
1.00 a 3.67
bc 5.67
bc
3.44
b
JOG 11-10
1.67 a 4.33
b 6.33
b 4.11
bc
MBE-SP 1.67
a 2.33
cd 7.07
ab 3.69
b
NSIC 23
1.00 a 2.33
cd 6.33
b
3.22
bc
NSIC 31
1.00 a 2.33
cd 4.33
cd 2.56
bc
TAIWAN D
1.67 a 2.33
cd 3.67
d 2.56
bc
Inubi-CA 1.00
a 1.67
d 4.33
cd 2.33bc
L-Mean
1.33 bc 3.20
b
5.87 a 3.47
*Rating scale: 1 = no stress; 3 = 30% of the leaves wilted; 5 = 50% of the leaves
wilted; 7 = 80% of the leaves wilted; 9 = complete wilting and death of plants.
CV(%) = 5.09
*Mean with the same letters are not significantly different at 5% level by DMRT.
Effect of water stress level. Significant difference was observed on the
drought score of the plants as affected by the level of water stress (Table 17).
Genotypes under severe stress (80 cb) exhibited the highest drought score of
Screening And Evaluation Of Sweet potato Genotypes
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85
5.87. Genotypes under moderate stress condition had comparable drought score
with plants under normal condition. It was also observed that plants in the
normal condition or sufficient water showed wilting of leaves. This could be
attributed to the high temperature (39-43 oC) inside the greenhouse.
Interaction
effect. Genotypes and level of water stress interacted
significantly to affect drought scores (Figure 13). Genotypes under normal
condition (20 cb) had the lowest score ranging from 1.00 and 1.67. High
drought score is due to the depletion of water needed for turgidity brought
about by water stress and high temperature during conduct of the study.
Figure 17. Drought score as affected by the interaction of genotypes and level
of water stress.
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
86
Recovery
Rating
Effect of genotype. There were significant differences on the recovery
rating of the different genotypes (Table 18). Genotype Taiwan D had the highest
recovery rating but not significantly different with Inubi-CA. Genotypes JK 7-4,
JOG 11-10 and NSIC 31 were comparable with Taiwan D and Inubi- CA. The
lowest recovery rating was noted from MBE –SP. This conforms with the work
of Taligan and Tad-awan (2004) in potato that high recovery rating of cultivars
results after rewatering under greenhouse condition.
Effect of water level on stress. Level of water stress significantly affected
the recovery rating of the plants after rewatering. Genotypes under control
condition (20 cb) had the highest recovery rating followed by genotypes under
moderate stress condition( 60 cb) and the lowest recovery rating was observed
from genotypes under severe condition.
Interaction
effect. Significant interaction of genotypes and level of water
stress was observed on the recovery rating (Figure 18). All genotypes under
control condition (20 cb) and moderate stress condition (60 cb) had higher and
comparable recovery ratings ranging from 5.00 to 9.00 and the lowest recovery
rating was observed from genotypes under severe stress condition (60 cb). It was
also observed that genotypes Taiwan D and Inubi–CA under severe stress
condition (80 cb) had recovery ratings comparable with the control and moderate
stress condition. This could be attributed to the effect of genotypic characteristic
Screening And Evaluation Of Sweet potato Genotypes
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87
Table 18. Recovery rating of the 10 sweetpotato genotypes as affected by level
of water stress
RECOVERY
RATING
*
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
9.00 a 6.33
bc 3.67
c 6.33 bc
JK-7-1 9.00
a 7.67
ab 5.67
b 7.44
ab
JK-18-4 9.00
a 8.33
a 3.67
c 7.00
b
JK 23-1
9.00 a 7.00
ab 5.00 bc 7.00
b
JOG 11-10
9.00 a 7.67
ab 5.67
b 7.44
ab
MBE-SP 9.00
a 5.00
c 3.67
c 5.89
c
NSIC 23
8.33 a 7.00
ab 4.33
bc 6.56bc
NSIC 31
9.00 a 7.67
ab 5.00
bc 7.22
ab
TAIWAN D
9.00 a 8.33
a 8.33
a 8.56
a
Unubi -CA
9.00 a 8.33
a 7.67
a 8.33
a
L-Mean 8.93a
7.33 b
5.27 c
7.18
*Recovery rating : 1 = no recovery; 3 = 30% of the leaves recovered; 5 = 50%
of the leaves recovered; 7 = 80% of the leaves recovered; 9 = complete recovery
of the plants
CV(%)= 12.9
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
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88
of the plants and the responses to different levels of water stress. Sweetpotato as
described by O’Sullican (2002 ) is known as a relatively drought-tolerant crop, it
will tolerate brief periods of drought stress, recovering quickly when soil moisture
is restored.
Figure 18. Recovery rating as affected by the inteaction of genotypes and level of
water stress.
Relative Water Content
Effect of genotype. Relative water content (RWC) of the different
genotypes did not differ at 35 DAP. Highest RWC was obtained from genotypes
JK- 23-1 while the lowest was observed from Inubi-CA. Other genotypes had
RWC ranging from 36.93 to 55.36 %. This could be due to the mechanism of
genotypes that can regain turgidity rapidly over other genotypes. According to
Screening And Evaluation Of Sweet potato Genotypes
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89
Table 19. Relative water content of the 10 sweetpotato genotypes as affected by
level of water stress
RELATIVE WATER CONTENT (%)
LEVEL OF WATER STRESS
GENOTYPE
CONTROL MODERATE
SEVERE G- MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
44.46
45.32
51.01
46.93
JK-7-1
40.81
44.42
47.65
44.29
JK-18-4
42.60
42.60
50.13
44.16
JK 23-1
50.26
54.93
85.32
63.64
JOG 11-10
40.14
41.34
44.36
41.95
MBE-SP
28.93
38.63
43.24
36.93
NSIC 23
47.44
56.97
61.69
55.36
NSIC 31
40.22
40.95
49.63
43.60
TAIWAN- D
42.91
39.27
46.91
43.03
Inubi-CA
27.49
27.87
43.07
32.81
L-Mean
40.28
43.23
52.30
45.27
CV(%)= 5.38
*Means with the same letters are not significantly different at 5% level by
DMRT.
Laure et al. (2009) plants were able to regain turgidity to certain extent and
slowly loose moisture as the stress continued until harvest.
Effect of water stress level. No significant differences were observed
among the levels of water stress on relative water content at 35 DAP (Table 9).
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
90
Plants subjected to severe stress (80 cb) gave the highest RWC followed by
control (20 cb) and moderate stress (60 cb) .
Interaction effect. Results show no significant interaction of genotypes
and level of water stress on RWC at 30 DAP. Genotype JK -23-1 under severe
stress condition (80 cb) had the highest RWC while the lowest was Inubi –CA
normal condition ( 20 cb). Other treatment combinations had RWC ranging
from 37.27 to 55.34 %.
Net Assimilation Rate
Effect of genotype. Net assimilation rate (NAR) of the different
genotypes was greatly affected at 35, 50 and 65 DAP. NSIC 23 exhibited the
highest NAR followed by JK-18-4 but not significantly different with NSIC 23.
Genotype JOG 11-10 had comparable NAR with NSIC 23 and JK-18-4. The
lowest NAR was observed from genotype MBE-SP. At 70 DAP, it was observed
that most genotypes had an increased NAR except for genotype Inubi-CA.
Genotype JK 23-1 had the highest NAR with a mean 4.93 followed by JK 18-4,
but these genotypes were not significantly different.
The NAR of all genotypes at 65 DAP had increased. Genotype JK 18-4
had the highest NAR which was not significantly different with JK 7-4. JOG 11-
10, Inubi –CA and JK 23-1 had comparable NAR with JK18-4 and JK 7- 4, while
the lowest NAR was observed from genotype BSU#1. Results indicate that all
genotypes had an increased dry weight accumulation per unit area of assimilate
Screening And Evaluation Of Sweet potato Genotypes
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91
Table 20. Net assimilation rate (NAR ) of 10 selected sweetpotato genotypes at
35 DAP as affected by level of water stress
NET ASSIMILATION RATE (%)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
2.94
2.34
1.70
2.33d
JK-7-1 3.33
2.92
2.27
2.84c
G10- JK-18-4
4.18
3.85
3.54
3.89a
JK 23-1
3.55
2.69
2.05
2.76cd
JOG 11-10
4.11
3.76 3.18
3.69ab
MBE-SP 4.37
3.19 2.26
3.27b
NSIC 23
4.66
3.74
3.49
3.96a
NSIC 31
3.02
2.52
2.28
2.61cd
TAIWAN D
3.44
3.01
1.85
2.77cd
Inubi – CA
3.68
3.46
2.82
3.32b
Mean
3.78a
3.15b
2.54 c
3.14
CV(%) =14.1
*Means with the same letters are not significantly different at 5% level by DMRT.
per unit of time. According to Fitter and Hay (1981) net assimilation rate or the
dry matter accumulation rate per unit leaf area is one of the useful parameters on
growth analysis, which influence the increase in plant weight per unit area of
assimilatory tissue (usually leaf area: AL ) per unit of time. It was observed that
Screening And Evaluation Of Sweet potato Genotypes
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92
NAR of the genotypes increased as plants mature regardless of water stress level.
Hunt (1978) mentioned that NAR is not constant with time but show downward
drift with plant age, and the age drift is accelerated by unfavorable environment.
Genotype and dry matter gain per unit leaf surface decreases as new leaves are
added due to mutual shading. Also, NAR decreases at more than 50 days old
leaves since photosynthesis decreases (Zaag, 1992).
Effect of water stress level. Significant differences were noted on NAR
of the plants at 35, 50 and 65 DAP as affected by level of water stress (Table 20,
Table 21 and Table 22). NAR of all genotypes decreased with increasing water
stress at 35, 50 and 65 DAP. Lowest NAR was observed from genotypes under
severe stress. Based on the study of Van Heerden (2008), restricted water supply
leads to inhibition of CO2 assimilation and photosynthesis through stomatal
closure. Further, drought stress decreased leaf area duration, cumulative water
transpired, net assimilation rate (Simane et al., 1993). This may explain the
decreasing trend in the net assimilation rates of sweetpotato with increasing water
stress.
Most of the genotypes under moderate stress had an increased NAR
except for genotype Inubi-CA which did not increase in NAR from 35 up to 50
DAP . Genotypes NSIC 31 and JOG 11-10 showed a decrease in NAR with
from 35 to 50 DAP.
Screening And Evaluation Of Sweet potato Genotypes
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93
Table 21. Net assimilation rate (NAR ) of the 10 sweetpotato selected genotypes
at 50 DAP as affected by level of water stress
NET ASSIMILATION RATE (%)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
3.04
2.74
1.68
4.16
JK-7-1 3.83
3.62
2.77
3.41
JK-18-4 5.27
4.85
4.56
4.89
JK 23-1
4.95
5.20
4.63
4.93
JOG 11-10
4.92
2.86
3.88
3.89
MBE-SP 4.96
4.07
3.37
4.13
NSIC 23
5.07
4.88
3.47
4.49
NSIC 31
3.39
2.01
2.47
2.62
TAIWAN D
3.63
3.39
2.10
3.04
Inubi -CA
3.41
3.46
2.82
3.23
L- Mean
4.25
3.21
3.18
6.88
CV(%) = 22.9
*Means with the same letters are not significantly different at 5% level by DMRT.
Interaction
effect. The interaction of genotypes and level of water stress
did not significantly affect the NAR at 35, 50 and 65 DAP. All genotypes
subjected to level of water stress had an increased NAR from 35 up to 65 DAP.
Screening And Evaluation Of Sweet potato Genotypes
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94
Table 22. Net assimilation rate (NAR ) of the 10 sweetpotato selected genotypes
at 65 DAP as affected by level of water stress
NET ASSIMILATION RATE (%)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
3.45
3.31
3.20
3.32 d
JK-7-1
6.88
5.46
5.02
5.79 a
JK-18-4
6.67
5.52
5.34
5.84 a
JK 23-1
5.30
5.00
4.84
5.05 abc
JOG 11-10
5.63
5.42
5.31
5.46 ab
MBE-SP
5.82
4.47
4.25
4.85 bc
NSIC 23
5.93
5.07
3.57
4.86 bc
NSIC 31
5.41
4.54
4.37
4.77 bc
TAIWAN – D
3.92
5.04
4.08
4.34c
Inubi-CA 5.58
4.98
4.65
5.07 abc
L- Mean
5.46a
4.88b
4.46c
4.93
CV(%)= 16.1
*Means with the same letters are not significantly different at 5% level by DMRT
Screening And Evaluation Of Sweet potato Genotypes
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Growth Parameters
Plant
Vigor
Effect of genotype. There were remarkable differences on plant vigor
among the different genotypes at 30 DAP (Table 23). Genotypes JOG 11-10,
NSIC 23, NSIC 31, Unubi-CA, Taiwan D, JK 7-4 and MBE- SP exhibited
highly vigorous growth. Genotypes JK 18- 4 and BSU # 1 had moderate vigor
rates.
Level of water stress effect. Plant vigor at 30 DAP was not significantly
affected by level of water stress (Table 23), although the highest plant vigor rating
was observed from genotypes under moderate stress condition (60 cb) with 4.77
(highly vigorous).
Interaction effect. Genotypes and level of water stress did not
significantly affect plant vigor at 30 DAP. Genotypes JK 7-1, JOG 11-10, NSIC
31, Taiwan D and Inubi –CA under any level of water stress had highly
vigorous growth. The least plant vigor was observed from genotype BSU # 1
under severe stress. Plant vigor is affected primarily by inherent characteristic;
secondary is the environment where the crop is grown (OSU, 1997).
Screening And Evaluation Of Sweet potato Genotypes
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96
Table 23. Plant vigor of the 10 sweetpotato genotypes as affected level of
water stress
PLANT
VIGOR
*
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
3.67
4.00
3.33
3.67 c
JK-7-1
5.00
5.00
5.00
5.00 a
JK-18-4
4.33
4.33
4.33
4.33 b
JK 23-1
4.67
4.67
4.67
4.67 ab
JOG 11-10
5.00
5.00
5.00
5.00 a
MBE-SP
4.67
4.67
5.00
4.78 a
NSIC 23
5.00
5.00
5.00
5.00 a
NSIC 31
5.00
5.00
5.00
5.00 a
TAIWAN- D
5.00
5.00
5.00
5.00 a
Inubi –CA
5.00
5.00
5.00
5.00 a
L-Mean 4.73a
4.77a
4.73a
4.73
Plant Vigor Rating: 5= Highly vigorous; 4= Moderately stress; 3= Vigorous; 2 =
Less vigorous; 1 = Poor vigor.
CV(%)=7.8
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
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Vine length at 35 DAP
Effect of genotype. Vine length significantly varied at 35 DAP among the
different genotypes (Table 24). Genotype JK 7- 4 exhibited the longest vines
but not significantly different with genotypes JK 23-1, NSIC 23, BSU # 1, and
Inubi- CA. The shortest vines were observed from JK 18-4.
Effect of water level of stress. Vine length at 35 days was not
significantly affected by the level of water stress ( Table 24). Although it can be
seen that genotypes under severe stress condition (80 cb) had the longest vines
followed by genotypes under moderate stress (60 cb) while genotypes under
control condition (20 cb) the shortest vines. Varied vine lengths could be due to
the soil moisture used for cell elongation.
Interaction
effect. The interaction of genotypes and level of water stress
did not significantly affect the vine length 35 DAP. Genotype JK 7-4 under
severe stress condition (80 cb) was noted to have the longest vines. Vine growth
could be due to the genotypic characteristic affected by environment. In the case
of JK producing long vines, the condition is possible. Other treatment
combinations had lengths ranging from 59.33 cm to 149.07 cm.
Screening And Evaluation Of Sweet potato Genotypes
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98
Table 24. Vine length at 35 DAP of the 10 sweetpotato genotypes as affected
by level of water stress
VINE LENGTH (cm)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
131.47
157.27
135.27
138.00 a
JK- 7-1
135.07
127.27
180.73
147.69 a
JK-18-4 70.73
59.33
58.40
62.82 c
JK 23-1
138.60
154.93
147.07
146.87 a
JOG 11-10
113.73
128.00
134.20
125.31 a
MBE-SP
118.40
136.53
134.60
129.84 a
NSIC 23
129.60
137.80
149.07 138.82
a
NSIC 31
95.27
95.93
107.07
99.42 b
TAIWAN D
66.47
81.67 73.40
73.84
c
Inubi–CA
122.40
136.67 138.67
132.58 a
L-Mean
112.17 a 120.54
a 125.85
a 119.52
CV(%) =19.7
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
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99
Vine length at 70 and 105 DAP
Effect of genotype. Genotypes significantly varied in their vine length at
70 DAP (Table 25). Genotype BSU # 1 exhibited the longest vines at 70 DAP
followed by Inubi–CA. Genotypes JK 7-4, MBE –SP, JK 23-1 and JOG 11-10
had comparable vine lengths with BSU #1 and Inubi –CA. The shortest vines
were observed from genotype JK 18-4. It also observed that all genotypes
under different level of water stress had increased in vine length from 35 to 70
DAP. Vine length is primarily a genotypic characteristic (OSU, 1997), however,
different genotypes have different sensitivity to the environment. For instance
Taiwan D and JK 18-4 produce short vines to conserve water, thus coping with
water stress. Other genotypes like BSU #1 and Inubi-CA produce long vines also
a coping mechanism by more roots per node as the vine creeps on the ground.
At 105 DAP genotype Inubi- CA registered the longest vines but not
significantly different with BSU #1. Genotypes MBE-SP, JOG 11-10, JK23-1
and JK 7-4 had comparable vine lengths with Inubi - CA and BSU # 1.
The adaptive mechanism of sweetpotato to drought condition include vine
length. The vines elongate with increasing moisture stress. According to Hammett
et al. (1982), sweetpotatoes are considered moderately tolerant to drought
conditions due to their low plant growth habit and extensive root system. This is
supported by the data in Table 33 where root elongates with increasing moisture
stress.
Screening And Evaluation Of Sweet potato Genotypes
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100
Effect of water level of stress. Vine length at 70 DAP was significantly
affected by level of water stress (Table 25). Genotypes under severe stress
condition (60 cb) had the longest vines followed by genotypes under moderate
stress condition (60 cb), and the lowest vine length was observed from genotypes
under control condition (20 cb) .
Vine length at 105 DAP was significantly affected by level of water stress
(Table 26). Genotypes under moderate stress (60 cb) had the longest vines
followed by genotypes under severe stress condition (60 cb) and the lowest vine
length was observed from genotypes under control condition (20 cb).
Interaction
effect. The interaction of genotypes and level of water stress
did not significantly affect the vine length of the plant at 70 and 105 DAP.
Genotype Inubi –CA under severe stress condition (60 cb) produced the longest
vines while the shortest vines were observed from genotype Taiwan D under
severe stress (80 cb). Other treatment combinations had vine length ranging from
151.15 cm to 338.13 cm.
Screening And Evaluation Of Sweet potato Genotypes
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101
Table 25. Vine length (cm) at 70 DAP of 10 selected sweetpotato genotypes as
affected by level of water stress
VINE LENGTH (cm)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
271.37
248.52
262.60
260.83 a
JK- 7-1
231.76
255.26
264.38
250.47 ab
JK-18-4
151.15
166.07
170.71
162.64 d
JK 23-1
213.12
231.55
249.72
231.40 abc
JOG 11-10
210.74
229.46
246.38
228.86 abc
MBE-SP
218.42
249.93
272.29
246.88 abc
NSIC 23
188.48
204.03
243.02
211.84 bc
NSIC 31
205.96
195.98
228.75
210.23 c
TAIWAN- D
145.42
175.82
186.29
169.18 d
Inubi -CA
219.90
274.10
285.60
259.86 a
L-Mean
205.63c 223.05
b
240.97 a
CV(%)= 16.5
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
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102
Table 26. Vine length (cm) at 105 DAP of the10 selected sweetpotato genotypes
as affected by level of water stress
VINE LENGTH (cm)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
385.87
442.40
345.47
391.24 a
JK- 7-1
307.00
322.40
338.13
322.51 ab
JK-18-4
216.27
462.80
203.40
294.16 b
JK 23-1
285.80
286.93
335.47
302.73 ab
JOG 11-10
279.33
305.00
333.20
305.84 ab
MBE-SP
296.40
340.60
287.47
308.16 ab
NSIC 23
257.47
303.67
300.60
287.24 b
NSIC 31
262.80
262.93
278.80
268.18 bc
TAIWAN- D
214.93
229.93
150.20
198.36 c
Inubi-CA
360.20
462.80
352.40
391.80 a
L-Mean
286.61 b 341.95
a 292.51
b
CV(%) = 16.5
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
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103
Number of Vine Cuttings per plant
Effect of genotype. Number of vine per plant was significantly
different among the genotypes (Table 27). Genotype BSU # 1 had the most
vines while the lowest vine number was observed from genotype Taiwan D.
Table 27. Vine number cutting per plant of the 10 selected sweetpotato
genotypes as affected by level of water stress
NUMBER OF VINES
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
7.71 a
8.84 a
4.91 a
7.82 a
JK- 7-1
6.14 a
6.44 a 6.76
a
6.45 ab
JK-18-4 4.32
a 9.25
a 4.06
a
5.88 b
JK 23-1
5.72 a
5.73 a
6.72 a
6.06 ab
JOG 11-10
5.58 a
6.10 a
6.66 a
6.11 ab
MBE-SP 5.87
a
6.80 a 5.75
a
6.14 ab
NSIC 23
5.15 a
6.07 a
6.01 a 5.74
b
NSIC 31
5.26 a
5.26 a
5.57 a
5.36 bc
TAIWAN- D
4.30 a
4.59 a
3.00 a
3.96 c
Inubi –CA
7.20 a
9.25 a
7.07 a
7.83 a
L- Mean
5.72 b
6.83 a 5.86
b 6.14
CV(%) = 4.14
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
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Effect of water stress level. The number of vine cuttings was significantly
affected by level of water stress. Genotypes under moderate stress condition
produced more number of vines than genotypes under normal.
Interaction
effect. Number of vine cuttings of plants as affected by the
genotypes and level of water stress was not significant. Although it can be seen
that genotypes JK 7-1 and Inubi–CA under moderate stress produced more
number of vine cuttings while the lowest number of vine cuttings was observed
from genotypes Taiwan D under severe stress condition.
Vine Weight per Plant
Effect of genotype. Vine weight was significantly different among the
genotypes (Table 28). The highest vine yield was observed from genotype NSIC
31 followed by Inubi-CA. Lowest vine yield was observed from JK -18-4.
Effect of level of water stress. Vine weight was significantly affected by
level of water stress (Table 28). Genotypes under moderate stress registered the
heaviest vine compared to genotypes under normal condition and genotypes
under severe stress condition.
Interaction
effect. Vine yield of plant as affected by genotypes and level
of water stress was significant (Figure 19). Genotype NSIC 31 produced the
heaviest vines under any level of water stress while the lowest was observed
from genotype JK 18-4. Other treatment combinations had vine weights ranging
from 376.33 to 845.00 g.
Screening And Evaluation Of Sweet potato Genotypes
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105
Table 28. Weight of vine per plant of the 10 selected sweetpotato genotypes as
affected by level of water stress
VINE WEIGHT (g)
LEVEL OF WATER STRESS
GENOTYPE CONTROL MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
484.67 de
592.00d 433.65e 503.44d
JK- 7-1
499.00 d
582.33d 441.33e 507.56d
JK-18-4 376.33
f
447.33e
266.00g
363.22f
JK 23-1
501.33 d
81.33 d
425.33 e
502.67 d
JOG 11-10
547.67 c
716.33c
458.67 de
574.22cd
MBE-SP 457.67
e
571.67d
361.00f 463.44
e
NSIC 23
473.00 de
560.67 d 508.67c 514.11d
NSIC 31
845.00a 928.33a 755.00a 842.78
a
TAIWAN- D
580.33c
727.67c
485.33cd 597.78c
Inubi –CA
691.00b
774.00b
678.33b 714.44b
L- Mean
545.60b
648.17 a 481.33
c
558.37
CV(%) = 4.0
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
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106
Figure 19. Vine weight of sweetpotato genotypes as affected by water stress level
Leaf area
Effect of genotype. Significant differences were noted on the area per
leaf of the different genotypes at 35, 50 and 65 DAP (Table 29, 30 and 31). All
genotypes had an increase area per leaf from 35 to 65 DAP.
Genotype BSU# 1 was noted to have the highest leaf area at 35 DAP.
Genotypes NSIC 23, Taiwan D, JK 23-1, JOG 11-10 and Inubi-CA had
comparable leaf area with BSU #1. The lowest leaf area was observed from
genotypes MBE-SP.
Genotypes BSU # 1 registered the highest leaf area but not significantly
different with Inubi – CA. Genotypes JK 7-4, JK 23-1, MBE-SP and JOG -11-10
Screening And Evaluation Of Sweet potato Genotypes
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107
were comparable with BSU #1 and Inubi- CA. The lowest leaf area was
observed from genotypes Taiwan D.
At 65 DAP genotype Inubi- CA had a mean of 310.56 while the lowest
leaf area was observed from JK 18-4.
Level of water stress effect. Area per leaf at 35 DAP was not greatly
affected by level of water stress. Area per leaf of genotypes under moderate
stress (60 cb) registered the highest followed by genotypes under control
condition (20 cb) while the lowest leaf area was observed from genotypes under
severe stress condition (80 cb). The results conforms with the study of
Mickelbart (2010) that the leaf characteristic of drought tolerant plants are
characterized as having small leaves, with leaf waxes, and minimal leaf area all
lead to reduced water loss, and therefore, drought tolerance. Tongket et al. (1991)
also found that the response of water stress in earlier stage in sweetpotato
inhibited the leaf growth than the root growth. Water stress caused a reduction of
leaf size in Centennial variety and in leaf number in other genotypes of
sweetpotato.
Level of water stress significantly affected the area per leaf at 50 and 65
DAP (Table 28 and 29). Leaf area of all genotypes under different levels of water
stress increased. Genotypes under moderate (60 cb) registered the highest leaf
area followed by genotypes under control condition (20 cb) while the lowest
leaf area was observed from genotypes under severe stress condition (80 cb).
Screening And Evaluation Of Sweet potato Genotypes
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108
Table 29. Leaf area (cm2) at 35 DAP of the 10 sweetpotato selected genotypes
as affected by level of water stress
LEAF AREA (cm2)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
101.70
87.51
88.76
92.66 a
JK- 7-4
42.85
64.98
55.98
54.60 c
JK-18-4
57.98
58.71
65.57
61.09 bc
JK 23-1
85.80
68.54
77.27 77.20
ab
JOG 11-10
79.83
76.54
63.11
73.16 abc
MBE-SP
64.18
55.81
42.33
54.11 c
NSIC 23
76.13
89.58
86.42 84.04
ab
NSIC 31
70.28
68.85
60.80
66.64 bc
TAIWAN- D
88.02
80.23
83.04
83.76 ab
Inubi –CA
76.70
71.48
67.25
71.81 abc
L-Mean
74.35 a 72.22
a 69.15
a 71.91
CV(%) =5.55
*Means with the same letters are not significantly different at 5% level by DMRT.
Water deficit or insufficient water supply inhibits cell division and expansion
resulting in the production of smaller leaves (Zaag, 1992; ICPRE and UI-CALS,
2002; Pritchard and Amthor, 2005).
Screening And Evaluation Of Sweet potato Genotypes
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109
Table 30. Leaf area (cm2) at 50 DAP of the 10 selected sweetpotato genotypes
as affected by level of water stress
LEAF AREA (cm2)
LEVEL OF WATER STRESS
GENOTYPE
CONTROL MODERATE
SEVERE G- MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
259.40 a 242.47 a 296.00
a 265.96 a
JK- 7-1
218.33 ab 258.60
a 220.73
ab 232.56
ab
JK-18-4 142.40
b 130.67
bc 154.00
b 142.36
cd
JK 23-1
219.87 ab 207.53
ab 234.13
ab 220.51
ab
JOG 11-10
201.07 ab 233.20
a 27.07
ab 217.11
ab
MBE-SP 203.00
ab 210.60
ab 238.13
ab 217.24
ab
NSIC 23
176.80 ab 220.27
ab 187.07
b 194.71
b
NSIC 31
194.80 ab 190.27
abc 170.93
b 185.33
bc
TAIWAN- D
135.20 b 106.13
c 161.60
b 134.31
d
Inubi-CA 237.47
a 243.27
a 282.73
a 254.49
a
L-Mean
198.83
204.30
216.24
CV (%) =5.67
*Means with the same letters are not significantly different at 5% level by
DMRT.
Interaction
effect. Area per leaf of genotypes at 35 and 65 DAP was not
remarkably affected by the interaction of genotypes and level of water stress
(Table 27 and 29). Although the highest leaf area was observed from genotype
Screening And Evaluation Of Sweet potato Genotypes
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110
Table 31. Leaf area (cm2) at 65 DAP of the 10 selected sweetpotato genotypes as
affected by level of water stress
LEAF AREA (cm2)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
290.25
257.29
221.21
256.25 cd
JK- 7-1
304.39
274.48
245.31
274.73 bc
JK-18-4
270.96
233.26
203.11
235.78 d
JK 23-1
315.08
250.11
229.77
264.99 c
JOG 11-10
300.04
250.90
233.78
261.58 c
MBE-SP
289.86
257.49
240.89
262.75 c
NSIC 23
267.04
251.81
237.26
252.03 cd
NSIC 31
313.48
282.11
268.15
287.91 b
TAIWAN- D
265.70
234.52
210.16
236.79 d
Inubi-CA
352.69
309.49
269.48
310.56 a
L- Mean
296.95a 260.15b
235.91c
CV(%) = 8.0
*Means with the same letters are not significantly different at 5% level by DMRT.
BSU #1 under normal condition (20 cb) while the lowest leaf area was observed
from genotype MBE-SP under severe stress (80 cb). Other treatment combination
had the leaf area ranging from 42.85 to 89.58 cm2.
Screening And Evaluation Of Sweet potato Genotypes
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111
Leaf Area Index
Effect of genotype. Genotypes significantly differ in their leaf area index
(LAI) at 35, 50 and 65 DAP (Table 32,33 and 34). All genotypes used had an
increase LAI at 35, 50 up to 65 DAP having vigorous lateral shoots.
Table 32. Leaf area index at 35 DAP of the 10 selected sweetpotato genotypes
as affected by level of water stress
LEAF AREA INDEX
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
3.09
4.98
2.93
3.67 a
JK- 7-1
1.50
1.23
1.99
1.57 c
JK-18-4
1.51
1.56
1.27
1.44 c
JK 23-1
3.70
3.12
2.86
3.22 ab
JOG 11-10
2.48
2.92
2.02
2.47 bc
MBE-SP
1.22
1.98
1.59
1.60 c
NSIC 23
1.98
2.22
2.12
2.11 c
NSIC 31
2.17
1.80
1.99
1.99 c
TAIWAN- D
1.68
2.90
2.10
2.23 bc
Inubi-CA
1.89
2.53
1.59
2.00 c
L-Mean
2.12
2.52
2.05
CV(%) – 8.6
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
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112
Table 33. Leaf area index at 50 DAP of 10 selected sweetpotato genotypes as
affected by level of water stress
LEAF AREA INDEX
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
10.23 a
8.74 a
8.44 a
9.14 a
JK- 7-1
3.52 a
5.60 a
2.26 a
3.79 de
JK-18-4 3.93
a
4.90 a
3.19 a 4.00
d
JK 23-1
6.77 a
8.04 a
4.63 a
6.48 c
JOG 11-10
7.74 a
9.66 a
6.00 a
7.80 b
MBE-SP 2.63
a
3.48 a
1.87 a 2.66
e
NSIC 23
3.54 a
4.28 a
3.11 a
3.64 de
NSIC 31
5.82 a
6.30 a
4.63 a
5.58 c
TAIWAN- D
3.04 a
3.08 a
2.49 a
2.87 de
Inubi –CA
6.49 a
7.71 a
5.40 a
6.53 c
L-MEAN
5.37 b 6.18
a
4.20 c
CV(%) = 6.55
*Means with the same letters are not significantly different at 5% level by DMRT.
Results show significant differences among genotypes for LAI. Genotypes BSU#
1 exhibited the largest LAI but comparable with JK-23-1. The smallest LAI was
obtained from genotype JK-18-4 at 35 DAP. This could be due to shedding of
leaves and heavy infestation of cutworms.
Screening And Evaluation Of Sweet potato Genotypes
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113
Table 34. Leaf area index at 65 DAP of the 10 selected sweetpotato genotypes
as affected by level of water stress
LEAF AREA INDEX
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
14.39 a
13.19 a
15.92 a
14.50 a
JK- 7-4
12.61 a
8.40 a 13.73
a
11.58 abc
JK-18-4 5.98
a
9.80 b 8.29
a 8.02
bc
JK 23-1
10.88 a 13.58
a
15.30 a
13.25 ab
JOG 11-10
13.28 a
12.76 a
11.70 a
12.58 abc
MBE-SP 12.28 a
18.49 a
7.24 a 12.67
abc
NSIC 23
9.58 a 5.62
a 5.62
a 6.94
c
NSIC 31
15.28 a
8.86 a
12.27 a
12.14 abc
TAIWAN- D
4.18 a
10.92 a
4.95 a 6.69
c
Inubi -CA
9.97 a
23.38 a 12.92
a
15.43 a
L- Mean
10.98b
12.50a
10.80 c
CV(%) = 24.2
*Means with the same letters are not significantly different at 5% level by DMRT.
At 50 DAP, BSU#1 had the highest leaf area index while the lowest was
from MBE-SP and Taiwan-D at 50 and 65 DAP.
Level of water stress effect. LAI at 35 DAP was not significantly affected
by level of water stress although it is noted that plants under normal condition
Screening And Evaluation Of Sweet potato Genotypes
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114
(20 cb) registered the highest LAI. The lowest LAI was observed from
genotypes under severe stress condition (80 cb).
At 50 and 65 DAP, highest LAI was observed from moderate water stress..
This shows that sweetpotato can tolerate moderate stress condition, as shown by
normal leaf development. But at severe stress, leaf development is affected to an
extent that leaf development is reduced. This could be attributed to the defense
mechanism of having small leaves against water stress. As stated by
Akyeampong (1985), drought-stressed leaves were smaller than the unstressed
leaves in the case of cowpea.
Interaction effect. The interaction of genotypes and level of water stress
did not significantly affect the LAI of plants at 35 , 50 and 65 DAP. At 35 DAP,
Genotype BSU#1 under moderate stress condition exhibited the highest LAI
while the lowest LAI was observed from genotype JK-18-4 under severe stress
condition while MBE-SP had the lowest LAI at 50 DAP.
Root Weight at Harvest
Effect of genotype. There were significant differences on the root weight
at harvest of the different genotypes (Table 35). Genotype NSIC 31 produced the
heaviest root, while the lowest was observed from genotype JK 7-4. Other
genotypes had the root weight ranging from 4.92 to 12.61 g.
Level of water stress effect. Root weight at harvest was significantly
affected by level of water stress (Table 33). Genotypes under severe stress
Screening And Evaluation Of Sweet potato Genotypes
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115
Table 35. Root weight at harvest of the 10 selected sweetpotato genotypes as
affected by level of water stress
ROOT
WEIGHT
(g)
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
5.54 e 3.54
g 5.68
g 4.92
f
JK- 7-1
5.04 f 2.63
h 6.86
f 4.84
f
JK-18-4 4.79
f 6.50
d
8.35 e 6.55
d
JK 23-1
4.77 f 5.24
f 6.53
f
5.52 e
JOG 11-10
5.81 de 5.73
e 8.81
d 6.79
d
MBE-SP 8.59
c 3.78
g 4.81
h 5.73
e
NSIC 23
4.77 f 6.74
d 6.55
f 6.01
e
NSIC 31
12.89 a 13.82
a 15.45
a 14.06
a
TAIWAN- D
6.17 d 8.67
c 9.34
c 8.06
c
Inubi -CA
10.88 b 12.52 b 14.45
b 12.61
b
L- Mean
6.92 b 6.92
b 8.68
a
CV(%) =3.0
*Mean with the same letters are not significantly different at 5% level of DMRT
condition (80 cb) registered the heaviest roots while the lowest was noted from
genotypes under control and moderate stress. This may be due to the mechanism
of the plants of having long roots during stress. Akyeampong (1985) and Hall
and Schulze (1980) found that in cowpea, increased root density and depth during
Screening And Evaluation Of Sweet potato Genotypes
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116
stress to exploit larger volume of soil to ensure the survival of the crop during
drought water stress and maintain plant status. Pritchard and Amthor (2005)
stressed that water stress sometimes stimulates root growth and this presumably
represents a mechanism to compensate for limited water supply. Moreover,
adaptation allow maximum growth and reproduction during dry period which
includes rapid development, C4 photosynthesis, high cuticular and stomatal
resistance to water loss, deep rooting systems, minimal leaf area, leaf rolling,
flagging and self shading.
Interaction effect. Genotypes and level of water stress interacted
significantly to affect root weight (Figure 20). Genotype NSIC 31 under severe
stress condition (60 cb) had the highest root weight while the lowest weight was
observed from genotype JK 23-1 under normal condition (20 cb).
Figure 20. Root weight as affected by the interaction of genotypes and level of
water stress
Screening And Evaluation Of Sweet potato Genotypes
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117
Root Length at harvest
Effect
genotype. There were significant differences on the root length of
the different genotypes (Table 36). Genotype JOG 11-10 exhibited the longest
roots while the shortest roots were obtained from NSIC 23.
Table 36. Root length at harvest of the 10 sweetpotato genotypes as affected by
level of water stress
ROOT
LENGTH
(cm)
LEVEL OF WATER STRESS
Genotype CONTROL
MODERATE
SEVERE
G-Mean
(20 cb)
(60 cb)
(80 cb)
BSU# 1
24.33 d 45.67
b 60.00
b 43.33 b
JK- 7-1
39.00 c 20.67
e 73.00
a 44.22
b
JK-18-4 35.33
c 44.33 b 57.67
b 45.78 b
JK 23-1
48.67 b 28.33
d 14.00
f 30.33
c
JOG 11-10
56.33 a 58.67
a 69.33
a 61.44
a
MBE-SP 53.00
a 55.00
a 21.00
e 43.00
b
NSIC 23
15.00 e 34.67
c 23.33
e 24.33
d
NSIC 31
37.00 c 14.33
f 30.33
d 27.22
d
TAIWAN- D
12.00 e 41.67
b 44.00
c 32.56
c
Inibi-CA 26.33
d 34.00
c 70.67
a 43.67
b
L-Mean
34.70 b 37.73
b 46.33
a
CV(%) = 6.1
*Means with same letters are not significantly different at 5% level by DMRT
Screening And Evaluation Of Sweet potato Genotypes
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118
Level of water stress effect. Length of roots at harvest was significantly
affected by level of water stress (Table 36). The longest roots were observed
from genotypes under severe stress condition (60 cb), followed by moderate
stress while the shortest roots were observed in genotypes under control
condition (20 cb).
Gurgel (2008) stated that indicators of drought tolerance is characterized
by having a deep root system and ability of leaf rolling since root play an
important role in controlling plant water status to avoid drought injury and leaves
roll under dry conditions, exposing less leaf surface to be in contact with dry air,
which was also observed during the study.
Fig. 15. Root length as affected by the interaction of genotypes and level of
water stress
Screening And Evaluation Of Sweet potato Genotypes
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119
Interaction effect. There was a significant interaction on the length of
roots as affected by genotypes and level of water stress (Figure 21). The longest
roots were observed from genotypes JK 7-4 under severe stress condition (60 cb)
while the shortest roots were observed from genotypes JK 23-1. Other treatment
combinations had root lengths ranging from 15.00 to 70.67 cm.
Incidence of Insect Pest and Diseases
Cutworm
Incidence
Effect
genotypes. Reaction to cutworm was significantly affected by
different genotypes (Table 37). Genotype JOG 11-10 had the lowest incidence
but not significantly different with genotypes JK 7-4, MBE-SP and BSU # 1. The
highest cutworm incidence was observed from JK 23-1.
Level of water stress effect. Incidence of cutworm was significantly
affected by level of water stress. Genotypes under severe stress condition (60 cb)
obtained the highest incidence rating of 2.73 followed by moderate stress
condition and the lowest rating was observed from genotypes under control
condition. It was observed that plants that were stressed are more susceptible to
cutworm infestation.
Interaction effect. Genotypes and level of water stress interacted significantly
with regards to incidence of cutworm (Figure 22). Genotype Inubi -CA under
severe stress incurred the highest incidence while the lowest rating was observed
Screening And Evaluation Of Sweet potato Genotypes
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Table 37. Cutworm incidence of the 10 selected sweetpotato genotypes as
affected by level of water stress
CUTWORM INCIDENCE *
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
1.00 b
2.00 bcd 2.33
cde 1.78
bc
JK- 7-1
1.00 b
1.67 cd 2.00
cde
1.56 bc
JK-18-4 1.00
b
1.00 d
4.00 ab 2.00b
JK 23-1
3.67 a
4.00 a
4.00 ab
3.89 a
JOG 11-10
1.00 b
1.67 cd
1.67 de
1.44 bc
MBE-SP 1.67
b
1.33 d
2.00 cde
1.67 bc
NSIC 23
3.33 a
3.33 ab
3.33 abc
3.33a
NSIC 31
3.33 a
2.33 bcd
1.00 e 2.22b
TAIWAN- D
1.67 b
2.33 bcd
2.67 bcd
2.22b
Inubi-CA 4.00
a
3.00 abc
4.33 a
3.78 a
L- Mean
2.17 b
2.27 b
2.73 a
2.39
* Rating scale: 1- no apparent injury; 2- injury confined to youngest leaf; 3- some
older leaves injured; 4-over 50% of the leaves injured; 5- over 90% of the leaves
injured
CV(%)- 10.56
*Means with the same letters are not significantly different at 5% level by
DMRT.
from genotypes JK 7 -4, JOG 11-10, BSU # 1 and JK 18-4 under control
condition.
Screening And Evaluation Of Sweet potato Genotypes
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121
Figure 22. Insect pest as affected by the interaction of genotypes and level of
water stress.
Leaf
Curling
Effect of genotype. The highest disease rating was observed from
genotype BSU#1 while genotypes JOG 11-10 and JK 18-7 had no disease
symptoms observed. JK 23-1 was susceptible to leaf curling while JOG 11-10
and JK 18-4 were highly resistant to leaf curling disease (Table 38).
Effect of water stress Level. Incidence of leaf curl disease was not
significantly affected by level of water stress ( Table 38). All genotypes under
different level of stress had ratings of 0.47 to 0.60, where there is 0 to 2.5 %
infection.
Screening And Evaluation Of Sweet potato Genotypes
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122
Table 38. Leaf curling incidence of 10 selected sweetpotato genotypes as
affected by level of water stress
LEAF CURLING INCIDENCE *
LEVEL OF WATER STRESS
GENOTYPE CONTROL
MODERATE
SEVERE
G-MEAN
(20 cb)
(60 cb)
(80 cb)
BSU# 1
1.33
2.00
2.33
1.89 a
JK- 7-1
0.67
0.33
0.33
0.44 bc
JK-18-4
0.00
0.00
0.00
0.00 c
JK 23-1
1.00
1.67
1.67
1.44 a
JOG 11-10
0.00
0.00
0.00
0.00 c
MBE-SP
0.33
0.33
0.33
0.33 bc
NSIC 23
0.67
0.33
0.67
0.56 b
NSIC 31
0.00
0.33
0.00
0.11 bc
TAIWAN- D
0.67
0.67
0.33
0.56 bc
Inubi –CA
0.00
0.33
0.33
0.22 bc
L- Mean
0.47 0.60
0.60
*Disease rating: 0-no disease; 1- trace 5% infection; 2-5 -15% infection; 4- 35 to
65% infection; 5 – 67.5 to 100% infection.
CV(%)= 12.76
*Means with the same letters are not significantly different at 5% level by DMRT.
Screening And Evaluation Of Sweet potato Genotypes
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123
Interaction
effect. The interaction of genotypes and level of water stress
did not significantly affect the incidence of viral disease. All genotypes under
different levels of water stress had ratings ranging from 0.00 to 2.33.
Correlation of Morphological, Physiological, Growth, Incidence of Insect pest
and Diseases and Vine yield Characters
The correlation coefficient between the vine yield at vine length (35, 70
and 105 DAP), leaf size (35, 50, and 65 DAP) leaf area index (35, 50 and 65 DAP)
of the different physiological, growth, morphological, incidence of pest and
diseases to vine yield are presented in Table 39.
Results revealed that drought score has negative significant correlation
with vine yield. This implies that genotypes lesser drought score produce more
vine yield. This collaborates with the findings of Ndler and Heuer (1995) that
there is a direct correlation between increasing drought and reduction in yield.
Drought causes wilting where cells become flaccid and leaves do not carry
assimilation normally (Dar,1980).
Root weight has positive significant correlation with vine yield. This
shows that genotypes with heavier roots have higher vine yield.
Screening And Evaluation Of Sweet potato Genotypes
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124
Table 39. Correlation coefficients of morphology, physiological, growth, insect
pest incidence, disease incidence to the vine yield.
COEFFICIENT OF
Characters
PROBABILITY
CORRELATION
No. of stomates in Abaxial
-.119ns .743
No. of stomates Adaxial
-.098ns .787
Drought score
-.688*
.028
Recovery rating
+471 ns .170
Disease incidence
.229ns .525
Insect Pest incidence
.+229 ns .524
Plant Vigor
+464 ns
.176
Root weight
+.883**
.001
Root length
-.279 ns .436
Leaf area index 65 DAP
+.289 ns .418
Leaf area index 50 DAP
+.217 ns .548
Leaf area index 35 DAP
+.019 ns .958
Leaf area 65 DAP
+.699*
.028
Leaf area 50 DAP
+.106 ns .772
Leaf area 35 DAP
+.166 ns .749
Vine Length at 35 DAP
+.007ns .985
Vine Length at 70 DAP
+.146ns .688
Vine Length 105 DAP
-.057ns .876
** = significant at 1% level
ns = not significant
* = significant at 5% level
Screening And Evaluation Of Sweet potato Genotypes
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125
Leaf area was significantly correlated with vine yield. This implies that
maintaining large leaves may help in increasing the vine yield of different
sweetpotato genotypes. This coincides with the view of Steppler (1967) that
among the contributory factor to high yield is the early establishment of large leaf
area.
Screening And Evaluation Of Sweet potato Genotypes
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126
SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
Summary
The study was composed of two experiments, first was screening of
sweetpotato genotypes using uni-green techniques under room temperature and
the second was evaluation of selected genotypes for drought resistance under
greenhouse condition. The study aimed to screen sweetpotato genotypes from
various germplasm sources for drought resistance; determine the effect of water
stress on the growth of genotypes; evaluate the growth and yield of selected
sweetpotato genotypes for drought resistance under greenhouse condition;
determine the interaction effect of sweetpotato genotypes and levels of water
stress and to correlate growth parameters with vine yield of the sweetpotato
genotypes.
Genotype
Forty sweetpotato genotypes were evaluated for drought resistance using
uni-green technique. All the parameters used in evaluating the characters of the
genotypes were significantly different.
Genotypes JK 18-4 and UPL-SP 4 had the most number of stomates/cm2
on the abaxial and adaxial portions of leaves. Out of the 40 genotypes 38 had
planophyle leaf orientation while two genotypes (Japanese inubi and JK 23-1) had
erectophyle leaf orientation. All genotypes’ responses to water deficit were
Screening And Evaluation Of Sweet potato Genotypes
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127
shedding, rolling and dropping. NSIC 28 had the biggest leaf size and produced
the shortest roots.
Genotype MBE-SP produced more number of roots while Genotype JK
23-1 produced the longest roots, highest recovery rating and lowest drought
score resulting in the highest RWC. The highest increment in shoot growth was
observed from genotype NSIC 24 and the lowest increment was observed from
UPL-SP 3. The tallest plants were observed from genotype JK 18-4
Out of forty sweetpotato genotypes ten genotypes selected based on the
highest recovery rating, lowest drought score. long roots, more number of roots
and small leaves.
Genotype JOG 11-10 had the most number of stomates-1cm2 on the
abaxial and adaxial portions of leaves. Out of 10 genotypes 9 were noted that had
planophyle leaf orientation and only genotype JK 23-1 had erectophyle leaf
orientation.
Genotype Inubi –CA had the lowest drought score, high recovery rating,
tallest plants at 70 and 105 DAP, biggest leaf area at 65 DAP and lowest relative
water content at 35DAP.
Taiwan D registered the highest recovery rating, high plant vigor, smallest
plant at 70 and 105 DAP (169.86cm and 198.63 and lowest vine yield. Genotype
JK 7-4 registered the tallest plants at 35 DAP.
Screening And Evaluation Of Sweet potato Genotypes
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JK 18-4 was noted to have the smallest plants at 35 DAP, lowest leaf area
at 50 and 65 DAP, smallest leaf area index and lowest disease rating. BSU # 1
registered the biggest leaf area at 35, 50 and 65 DAP, highest leaf area index
and highest vine yield. JK 23 -1 noted the highest relative water content but not
significantly different with the other genotypes and NSIC 23 produced the
shortest roots but heaviest root. Genotype JOG 11-10 produced the longest root
lowest insect infestation.
Five genotypes had characters that can be considered as adaptive
mechanism for water stress such as; small to medium leaf area, high leaf area
index, long roots, more roots, long vines, more of vines and high vine yield.
Genotypes JOG 11-10, Inubi-Ca, Taiwan D, NSIC 23 and JK 18-4 exhibited
these characters. .
Water Stress
Genotypes under not stressed (20 cb) registered the lowest drought score,
highest recovery rating; lowest relative water content; highly vigorous plants,
lowest vine length at 35 and 105 DAP; highest leaf area; lowest root weight;
lowest root length; moderate resistance to cutworm; and few vine cuttings.
Genotypes under moderate stress (60 cb) produced had moderate drought
score and recovery rating; lowest relative water content; highly vigorous; tallest
plants and biggest leaf area index.
Screening And Evaluation Of Sweet potato Genotypes
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129
Plants under severe water stress had the highest drought score; lowest
recovery rating; highest relative water content; lowest plant vigor rating; tallest
plants; smallest leaf area; smallest leaf area index; heaviest roots and the longest
roots.
Interaction of Genotype and Water Stress Level
Genotype JOG 11-10 under moderate stress had the highest stomata-1cm2
on the abaxial and adaxial portions of the leaves and genotype JK 18-4 under
control condition produced the least stomata-1cm2 on the abaxial and adaxial
portions of the leaves; JK 18-4 and JK 7-1 under severe stress were the highest
drought score and the lowest was Inubi-CA under moderate stress.
Taiwan D under severe stress produced the highest recovery rating and
lowest were JK 18-4 and BSU # 1 under severe stress and JK 23-1 under severe
stress produced the highest relative water content and the lowest Inubi –CA
under normal and moderate stress; lowest plant vigor was observed from
genotype BSU #1 under severe stress condition.
Correlation of Characters
Vine yield was positively correlated to leaf size at 65 DAP and root
weight. Drought score had negative significant correlated to vine yield.
Screening And Evaluation Of Sweet potato Genotypes
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130
Conclusions
Based on the results, the following conclusions are drawn:
1. Moderate water stress had negative effects on the morphological,
physiological and growth performance of the forty genotypes evaluated.
2. Plantlets under moderates stress produced smallest leaf area and leaf area
index, lowest drought score, high relative water content and smallest height
increment.
3. Ten best genotypes were selected such as NSIC 23,. NSIC 31, Taiwan D, JOG
11-10, JK 7-4, JK 18-4, JK 23-1, BSU #1 , MBE –SP and Inubi –CA which
exhibited drought resistant characteristics such as dropping and shedding of
leaves lower drought score, higher recovery rating, high RWC, medium to
small leaf area, and leaf area index and vigorous plants.
4. Plants under moderates stress and severe stress produced smallest leaf area
and leaf area index, heaviest roots, longest roots and highest RWC.
5. Production of sweetpotato can be still be feasible in soil with 60 cb soil
moisture matric potential .
6. Genotypes JOG 11-10, JK 18 -4, JK 7-4, Taiwan D, NSIC 31 and Inubi –CA
had drought resistant characteristic such as small leaf area and area index,
longest roots, low drought score , high recovery rating and more vine yield.
Screening And Evaluation Of Sweet potato Genotypes
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131
7. Significant positive correlation between leaf area at 65 DAP and root weight
with vine yield in 10 genotypes and negative significant correlation existed
in drought score to vine yield.
Recommendation
Considering the findings in study , the following are recommended:
1. Genotypes NSIC 23, NSIC 31, Taiwan D, JOG 11-10, JK 7-4, JK 18-4, JK
23-1, BSU #1 , MBE –SP and Inubi –CA can be planted under 60 cb soil
moisture matric potential.
2. When soil matric potential is 80 cb genotypes JOG 11-10, JK 18 -1, NSIC 23,
Taiwan D and Inubi –CA can be planted.
3. Characters significantly correlated with vine yield can be used as selection
indices for sweetpotato genotypes under water stress condition.
4. Further studies need to be undertaken during dry season for drought resistant
genotypes under field condition.
Screening And Evaluation Of Sweet potato Genotypes
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132
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APPENDICES
Appendix Study 1
APPENDIX TABLE 1. Analysis of variance for number of stomates on the
abaxial portion of leaf
SV DF
SS MS F
Treatment
79
85493.6
1082.2
518.42 **
Genotype ( G )
39
77978.9
1999.5
957.82 **
Treatment (T)
1
3744.6
3744.6
1793.82 **
VxT 39
3770.10
96.7
46.31
**
Error 160
334.0
2.1
TOTAL 239
85827.6
CV (%) = 1.7
** = significant at 1 % level
APPENDIX TABLE 2. Analysis of variance for number of stomates on the
adaxial portion of leaf
SV DF
SS MS F
Treatment
79
630.545
7.982
5.19 **
Genotype ( G )
39
595.614
15.272
9.93 **
Treatment (T)
1
14.915
14.915
9.69 **
VxT 39
20.016
0.1513
0.33ns
Error 160
246.195
1.539
TOTAL 239
876.740
CV(%) = 7.5
** = significant at 1 % level
ns
=
non
significant
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
136
Appendix Table 3. Analysis of variance for leaf area
SV DF
SS MS F
Treatment
79
137735
1743
178.36 **
Genotype ( G )
39
107488
2756
281.96 **
Treatment (T)
1
3018
3018
308.70 **
V x T
39
27229
698
71.43 **
Error 160
1564
10
TOTAL 239
139299
CV (%) = 7.8
** = significant at 1 % level
APPENDIX TABLE 4. Analysis of variance for root length
SV DF
SS MS F
Treatment
79
550.203
6.965
79.15 **
Genotype ( G )
39
432.091
11.079
125.92 **
Treatment (T)
1
102.534
102.534
1165.33 **
VxT
39
15.578
0.399
4.54 **
Error 160
14.078
0.088
TOTAL 239
564.281
CV (%) = 4.2
** = significant at 1 % level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
137
APPENDIX TABLE 5. Analysis of variance for number of roots
SV DF
SS MS F
Treatment
79
1218.40
15.42
14.69 **
Genotype ( G )
39
1087.90
27.89
26.57 **
Treatment (T)
1
14.50
14.50
13.81 **
VxT 39
116.00
2.97
2.83
**
Error 160
168.00
1.05
TOTAL 239
1386.40
CV (%) = 12.6
** = significant at 1 % level
APPENDIX TABLE 6. Analysis of variance for vine length before exposing to
drought
SV DF
SS MS
F
Treatment
79
2105.90
26.66
940.38 **
Genotype ( G )
39
1622.16
41.59
1467.30 **
Treatment (T)
1
14.73
14.73
519.50 **
VxT
39
469.01
12.03
424.24 **
Error
160
4.54
0.03
TOTAL 239
2110.43
CV (%) = 1.2
** = significant at 1% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
138
APPENDIX TABLE 7. Analysis of variance for vine length after drought
imposition
SV DF
SS MS
F
Treatment
79
2224.66
28.16
242.69 **
Genotype ( G )
39
1839.49
47.17
406.49 **
Treatment (T)
1
142.96
142.96
1232.04 **
VxT
39
242.21
6.21
53.52 **
Error 160
18.57
0.12
TOTAL 239
CV (%) = 2.1
** = significant at 1% level
APPENDIX TABLE 8. Analysis of variance for drought score
SV DF
SS MS F
Treatment
79
830.053
10.507
100.73 **
Genotype ( G )
39
254.702
6.531
62.61 **
Treatment (T)
1
320.351
320.351
3071.23 **
VxT
39
255.000
6.538
62.68 **
Error 160
16.689
0.104
TOTAL 239
846.742
CV (%) = 15.0
** = significant at 1% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
139
APPENDIX TABLE 9. Analysis of variance for recovery rating
SV DF
SS MS F
Treatment
79
294.782
3.731
226.94 **
Genotype ( G )
39
143.050
3.668
223.08 **
Treatment (T)
1
8.645
8.645
525.77 **
VxT 39
143.087
3.669
223.14
**
Error
160
2.631
0.016
TOTAL 239
297.413
CV (%) = 1.5
** = significant at 1% level
APPENDIX TABLE 10. Analysis of variance for relative water content
SV DF
SS MS F
Treatment
79 10286.10 130.2 18.83**
Genotype ( G )
39
8670.2
222.3
32.16 **
Treatment (T)
1
437.9
437.9
63.34 **
VxT
39
1178.0
30.2
4.37 **
Error 160
1106.10
6.9
TOTAL 239
11392.2
CV (%) = 9.6
** = significant at 1 % level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
140
APPENDIX TABLE 11. Analysis of variance for percentage of survival
SV DF
SS MS F
Treatment
79
2967.30
37.56
1452.68 **
Genotype ( G )
39
2501.70
64.15
2480.88 **
Treatment (T)
1
134.58
134.58
5204.94 **
VxT 39
331.02
8.49
328.27**
Error 160
4.14
0.03
TOTAL 239
2971.44
CV(%) = 0.2
** = significant at 1 % level
APPENDIX TABLE 12. Analysis of variance for vine length at 10 DAP
SV DF
SS MS F
Treatment
79
515.501
6.525
10.58 **
Genotype ( G )
39
400.938
10.280
16.67 **
Treatment (T)
1
2.933
2.933
4.75 *
VxT
39
111.630
2.862
4.64 **
Error
160
98.694
0.617
TOTAL 239
614.195
CV(%) =11.7
** = significant at 1 % level
* = significant at 5% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
141
APPENDIX TABLE 13. Analysis of variance for vine length at 20 DAP
SV DF
SS MS F
Treatment
79
1908.03
24.15
122.73 **
Genotype ( G )
39
1498.08
38.41
195.19 **
Treatment (T)
1
8.66
8.66
43.99 **
VxT
39
401.29
10.29
52.28 **
Error 160
31.49
0.20
TOTAL 239
1939.52
CV (%) = 3.5
** = significant at 1% level
APPENDIX TABLE 14. Analysis of variance for vine length at 30 DAP
SV DF
SS MS
F
Treatment
79
1734.47
21.96
87.54 **
Genotype ( G )
39
1512.52
38.78
154.64 **
Treatment (T)
1
2.98
2.98
11.89 **
VxT
39
218.97
5.61
22.39 **
Error
160
40.13
0.25
TOTAL 239
1774.60
CV (%) = 3.5
** = significant at 1% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
142
APPENDIX TABLE 15. Analysis of variance for vine length for 40 at DAP
SV DF
SS MS
F
Treatment
79
3058.46
38.71
92.20 **
Genotype ( G )
39
2091.60
53.63
127.72 **
Treatment (T)
1
593.71
593.71
1413.95 **
VxT 39
373.15
9.57
22.79
**
Error 160
67.18
0.42
TOTAL 239
3125.65
CV (%) = 3.7
** = significant at 1% level
APPENDIX TABLE 16. Analysis of variance for vine length for 50 at DAP
SV DF
SS MS
F
Treatment
79
6288.15
79.60
144.42 **
Genotype ( G )
39
2923.37
74.96
136.00 **
Treatment (T)
1
2572.25
2572.25
4667.11 **
VxT 39
792.53
20.32
36.87
**
Error 160
160
88.18
0.55
TOTAL 239
6376.34
CV (%) = 3.6
** = significant at 1% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
143
Appendix Study 2
APPENDIX TABLE 17. Analysis of variance for number of stomates on the
abaxial portion of leaves
SV DF
SS MS
F
Replication ( R )
2
11.4
5.7
2.27*
Treatment 29
37372.6
1288.7
742.67**
Genotype (G)
9
15320.2
1702.2
980.98**
Factor (B)
2
14866.3
7433.10
4283.62**
GxT 18
7186.2
399.2
230.07**
Error 58
100.6
1.7
TOTAL 89
37484.6
CV (%)= 1.3
** = significant at 1 % level
*
=
significant
at
5
%
level
APPENDIX TABLE 18. Analysis of variance for number of stomates on the
adaxial portion of leaves
SV DF
SS MS
F
Replication ( R )
2
11.4
5.7
2.27*
Treatment 29
37372.6
1288.7
742.67**
Genotype (G)
9
15320.2
1702.2
980.98**
Factor (B)
2
14866.3
7433.10
4283.62**
GxT 18
7186.2
399.2
230.07**
Error 58
100.6
1.7
TOTAL 89
37484.6
CV (%) = 1.3
** = significant at 1 % level
* = significant at 5 % level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
144
APPENDIX TABLE 19. Analysis of variance for drought score
SV DF
SS MS
F
Replication ( R )
2
10.4569800
5.2284900
4.84 *
Treatment 29
449.8982100
15.5137314
14.36
**
Genotype (G)
9
89.3772989
9.9308110
9.19 **
Factor (B)
2
312.4756467
156.2378233
144.64 **
GxT 18
48.0452644
2.6691814
2.47
**
Error 59
61.5724200
1.0802179
TOTAL 89
521.9276100
CV (%) = 5.09
** = significant at 1 % level
* = significant level at 5% level
APPENDIX TABLE 20. Analysis of variance for recovery rating
SV DF
SS MS F
Replication ( R )
2
1.1555556
0.5777778
< 1
Treatment 29
306.4888889
10.5685824
12.38
**
Genotype (G)
9
55.8222222
6.2024691
7.27 **
Factor (B)
2
202.7555556
101.3777778
118.76 **
GxT 18
47.9111111
2.6617284
3.12
**
Error 58
49.5111111
0.8536398
TOTAL 89
357.1555556
CV (%) = 12.9
** = significant at 1% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
145
APPENDIX TABLE 21. Analysis of variance for relative water content
SV DF
SS MS F
Replication ( R )
2
192.818
96.409
39.51 **
Treatment 29
37.326
1.287
0.53
ns
Genotype (G)
9
23.631
2.626
1.08 ns
Factor (B)
2
10.293
5.147
2.11 ns
GxT 18
3.401
0.189
0.18
ns
Error 58
141.523
2.440
TOTAL 89
371.666
CV (%) = 5.38
** = significant at 1 % level
ns
=
not
significant
APPENDIX TABLE 22. Analysis of variance for net assimilation rate at 35 DAP
SV DF
SS MS
F
Replication ( R )
2
0.8501
0.4251
2.17 ns
Treatment 29
50.2446
1.7325
8.83**
Genotype (G)
9
25.7474
2.8608
14.58**
Factor (B)
2
21.0662
10.5331
53.68**
GxT
18
3.4310
0.1906
<1
Error 58
11.3798
0.1962
TOTAL
89
62.4745
CV (%)= 14.1
** = significant at 1 % level
ns
=
not
significant
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
146
APPENDIX TABLE 23. Analysis of variance for net assimilation rate at 50
DAP
SV DF
SS MS
F
Replication ( R )
2
2.881
1.441
1.94ns
Treatment 29
91.117
3.142
4.24
**
Genotype (G)
9
54.363
6.040
8.14**
Factor (B)
2
17.746
8.873
11.96**
GxT 18
19.008
1.056
1.42ns
Error 58
43.024
0.742
TOTAL
89
137.022
CV(%)=22.9
* = significant at 5 % level
APPENDIX TABLE 24. Analysis of variance for net assimilation rate at 65 DAP
SV
DF
SS
MS
F
Replication ( R )
2
0.2693756
0.1346878
< 1
Treatment 29
71.3263789
2.4595303
3.89
**
Genotype (G)
9
43.6063567
4.8451507
7.67 **
Factor (B)
2
15. 0386689
7.5193344
11.90 **
GxT
18
12.6813533
0.7045196
1.11 ns
Error 58
36.6622911
0.6321085
TOTAL 89
108.2580456
CV(%) = 16.1
** = significant at 1 % level
ns = not significant
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
147
APPENDIX TABLE 25. Analysis of variance for plant vigor
SV DF
SS MS
F
Replication ( R )
2
0.82222222
0.41111111
3.04 ns
Treatment 29
16.45555556
0.56743295
4.20
**
Genotype (G)
9
15.56666667
1.72962963
12.79 **
Factor (B)
2
0.02222222
0.01111111
< 1
GxT
18
0.86666667
0.04814815
< 1
Error 58
7.84444444
0.13524904
TOTAL 89
25.12222222
CV (%) = 7.8
** = significant at 1% level
ns
=
not
significant
APPENDIX TABLE 26. Analysis of variance for vine length at 35 DAP
SV DF
SS
MS
F
Replication ( R )
2
531
265
< 1
Treatment 29
83446
2877
5.18
**
Genotype (G)
9
74438
8271
14.88 **
Factor (B)
2
2851
1426
2.56 ns
GxT 18
6157
342
<
0
Error 58
32248
556
TOTAL 89
116226
CV (%) = 19.7
** = significant at 1% level
ns
=
not
significant
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
148
APPENDIX TABLE 27. Analysis of variance for vine length at 70 DAP
SV DF
SS MS
F
Replication ( R )
2
9436
4718
3.47 *
Treatment 29
127371
4392
3.23
**
Genotype (G)
9
99418
11046
8.13 **
Factor (B)
2
18735
9367
6.89 **
GxT 18
9219
512
<
1ns
Error 58
78801
1359
TOTAL 89
215608
CV (%) = 16.5
** = significant at 1% level
*
=
significant level at 5% level
APPENDIX TABLE 28. Analysis of variance for vine length at 105 DAP
SV DF
SS MS
F
Replication ( R )
2
46455
23228
2.98 ns
Treatment 29
451748
155578
2.00
*
Genotype (G)
9
255741
28416
3.64 **
Factor (B)
2
55411
27705
3.55 *
GxT
18
140597
7811
1.00 ns
Error 58
452524
7802
TOTAL 89
950728
CV (%) = 28.8
** = significant at 1 % level
* = significant level at 5% level
ns = not significant
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
149
APPENDIX TABLE 29. Analysis for variance for leaf area at 35 DAP
SV DF
SS MS
F
Replication ( R )
2
0.316
0.158
< 1
Treatment 29
57.081
1.968
1.41
ns
Genotype (G)
9
43. 076
4.786
3.44 **
Factor (B)
2
0.925
0.463
< 1
GxT
18
13. 080
0.727
< 1
Error 58
80.801
1.393
TOTAL 89
CV (%) = 5.55
** = significant at 1% level
ns = significant
APPENDIX TABLE 31. Analysis of variance leaf area at 65 DAP
SV DF
SS MS F
Replication ( R )
2
23824
11912
26.33 **
Treatment 29
103081
3555
7.86
**
Genotype (G)
9
41415
4602
10.17 **
Factor (B)
2
56677
28338
62.63 **
GxT 18
4989
277
<
1
Error 58
26243
452
0.612
TOTAL 89
153148
CV(%) = 8.0
** = significant at 1 % level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
150
APPENDIX TABLE 32. Analysis of variance for leaf area index at 35 DAP
SV DF
SS MS
F
Replication ( R )
2
0.0046
0.0023
0.06 ns
Treatment 29
1.8280
0.0630
1.71
*
Genotype (G)
9
1.3719
0.1524
4.14 **
Factor (B)
2
0.1089
0.0544
1.48 ns
GxT
18
0.3473
0.0193
0. 52 ns
Error 58
2.1369
0.0368
TOTAL 89
3.9694
CV (%) = 8.6
** = significant at 1 % level
*= significant at 5 % level
APPENDIX TABLE 33. Analysis of variance for leaf area index at 50 DAP
SV DF
SS MS
F
Replication ( R )
2
3.1377
1.5688
2.82 ns
Treatment 29
21.8757
0.7543
1.36
ns
Genotype (G)
9
12.3013
1.3668
2.46 *
Factor (B)
2
0.6636
0.3318
0.60 ns
GxT 18
8.9108
0.4950
0.89
ns
Error 58
32.2534
0.5561
TOTAL 89
57.2667
CV(%) = 6.55
** = significant at 1 % level
* = significant at 5 % level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
151
APPENDIX TABLE 35. Analysis of variance for root weight at harvest
SV DF
SS
MS F
Replication ( R )
2
1.04
0.52
10.41 **
Treatment 29
1015.04
35.00
701.50
**
Genotype (G)
9
845.00
93.89
1881.71 **
Factor (B)
2
62.29
31.15
624.24 **
GxT 18
107.75
5.99
119.98
**
Error 58
2.89
TOTAL 89
1018.98
CV (%) = 3.0
** = significant at 1% level
APPENDIX TABLE 36. Analysis of variance for root length
SV DF
SS MS
F
Replication ( R )
2
7.6
3.8
< 1
Treatment 29
27795.8
958.5
166.25
**
Genotype (G)
9
9904.7
1100.5
189.50 **
Factor (B)
2
2185.0
1092.5
189.50 **
GxT 18
15706.2
872.6
151.35
**
Error 58
334.4
5.8
TOTAL 89
28137.8
CV (%) = 6.1
** = significant at 1% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
152
APPENDIX TABLE 37. Analysis of variance for cutworm incidence
SV DF
SS MS
F
Replication ( R )
2
3.756
1.878
2.54 ns
Treatment 29
106.722
3.680
4.97
**
Genotype (G)
9
69. 833
7.759
10.49 **
Factor (B)
2
5.489
2.744
3.71 *
GxT 18
31.400
1.744
2.36
**
Error 58
42.911
0.740
TOTAL 89
153.389
CV (%) = 36.0
** = significant at 1 % level
* = significant level at 5% level
ns = not significant
APPENDIX TABLE 38. Analysis of variance for leaf curled incidence
SV DF
SS MS F
Replication ( R )
2
0.0403
0.0201
3.94 *
Treatment 29
0.8063
0.0278
5.44
**
Genotype (G)
9
0.7277
0.0809
15.82 **
Factor (B)
2
0.0075
0.0037
< 1
GxT 18
0.0712
0.0040
<
1
Error 58
0.2965
0.0051
TOTAL 89
1.1431
CV (%) = 12.76
** = significant at 1% level
* = significant level at 5% level
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
153
APPENDIX TABLE 39. Analysis of variance for number of vine cuttings
SV DF
SS MS
F
Replication ( R )
2
0.4170
0.2085
3.22 *
Treatment 29
3.9376
0.1358
2.10
**
Genotype (G)
9
2.2626
0.2514
3.89 **
Factor (B)
2
0.4458
0.2229
3.45 *
GxT 18
1.2292
0.0683
1.06
ns
Error 58
3.7508
0.0647
TOTAL 89
8.1054
CV(%) = 4.14
** = significant at 1 % level
* = significant at 5 % level
APPENDIX TABLE 39. Analysis of variance for vine weight
SV DF
SS MS
F
Replication ( R )
2
1805
903
1.83 ns
Treatment 29
1971091
67969
137.69**
Genotype (G)
9
1483249
164805
333.86 **
Factor (B)
2
424835
212417
430.31 **
GxT 18
63007
3500
7.09**
Error 58
28631
494
TOTAL 89
20011527
CV(%) = 4.0
** = significant at 1 % level
ns = not significant
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
154
BIOGRAPHICAL SKETCH
The author is the eldest of four daughter of Villamor Cacal and Rosita
Velasco, Nipaco, Paniqui, Tarlac. She was born on July 12, 1975 in Nipaco,
Paniqui, Tarlac.
She finished her elementary education in Nipaco, Elementary School,
Paniqui, Tarlac, She enrolled in Balaoang National High School and graduated
as fist honorable mention. She spent her college days at Tarlac College of
Agriculture and obtained a degree of Bachelor of Science in Agriculture major in
Agronomy and minor in Crop Protection. During her college life she was a
recipient of Eduardo Cojuangco Foundation and a scholar of Shouichi Yoshida
Memorial Foundation. She finished her Master in Agriculture major in
Agronomy minor in Farming ystem in 2006 at Tarlac College of Agriculture. In
order to gain more knowledge she pursued her Ph.D in Agronomy minor in Rural
Development at Benguet State University.
After obtaining her bachelor’s degree she worked with the Uni-green
Incorporated as Researcher of Ornamental Plants and Japanese vegetable at, Lipa,
Batangas. In November, 1999 to 2002 she was a Science Research Assistant at
Pangasinan State University in Sta Maria, Pangasinan because of her willingness
to share her expertise on tissue culture to her Alma mater she transferred at
Tarlac College of Agriculture and now she is a faculty of the Institute of
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
155
Agriculture and Forestry and In-charge of the Tissue Culture Laboratory Project
of the College.
In 2000, she got married to Ruben P. Perey of Mendez, Cavite and
blessed two children: Julie Hanna and Jan Benedict.
Agnes
Cacal
Perey
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance / Agnes C. Perey. 2012
Uni-green Technique. . . . . . . . . . . . . . . . . .
29
Germplasm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
Establishment of Mother plants . . . . . . . . . . . . . . . . . . . . . . . . .
29
Experimental Design and treatments . . . . . . . . . . . . . . . . . . . . .
33
Preparation of Planting Materials . . . . . . . . . . . . . . . . . . . . . . . .
33
Preparation of Floral Foam and Single-node Planting Materials
34
Fertilizer Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
Drought Stress Imposition . . . . . . . . . . . . . . . . . . . . . . . . . . . .
35
Data Gathered . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . ..
36
Experiment ll. Evaluation of Selected Genotypes for Drought
Resistance under Greenhouse Condition . . .
39
Experimental Design and Treatments . . . . . . . . . . . . . . . . . . . .
40
Crop Establishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Drought Imposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Control of Insect Pest, Diseases . . . . . . . . . . . . . . . . . . . . . . . .
42
The Data Gathering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
42
Statistical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45
RESULTS AND DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
46
Experiment l. Screening of Sweetpotato Genotypes using
46
Uni-green Technique . . . . . . . . . . . . . . . . . . .
Morphological Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
46
Number of Stomates on the Abaxial Portion of Leaves
46
Number of Stomates on the Abaxial Portion of Leaves
48
Leaf Characters . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . .
50
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
Leaf Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
51
Roots Length. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
54
Number of Roots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
56
Length of Shoots Before and After Water Stress
Imposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
59
Physiological Parameters . . . . . . . . . . . . . . . . . . . . .. . . . . . . . .
63
Drought Score . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .
63
Recovery Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
65
Relative Water Content . . . . . . . . . . . . .. . . . . . . . . . . .
65
Other Growth Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
69
Percentage survival . . . . . . . . . . . . . . . .. . . . . . . . . . . . .
69
Plant Vigor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .
69
Plant Height every 10 days . . . . . . . . . . . . . . . . . . . . . .
71
Experiment ll. Evaluation of Selected Genotypes for drought
Resistance under Greenhouse Condition . . . . . . . . . . . . . .
76
Meteorological Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
76
Morphological Parameters . . . . . . . . . . . . . . . .. . . . . . . . . . . . .
77
Number of Stomates on the Abaxial Portion of Leaves
77
Number of Stomates on the Adaxial Portion of Leaves
80
Leaf Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
83
Physiological Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
83
Drought Score . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .
83
Recovery Rating . . . . . . . . . . . . . . . . . . . . . . . . . . .
86
Relative Water Content . . . . . . . . . . . . . . . . . . . . . . .
88
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
Net Assimilation Rate . . . . . . . . . . . . . . . . . . . . . . . .
90
Growth Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
95
Plant Vigor . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . .
95
Vine length at 35 DAP . . . . . . . . . . . . . . . . . . . . . . . . .
97
Vine length at 70 and 105 DAP . . . . . . . . . . . . . . . . . . .
99
Number of vine cuttings . . . . . . . . . . . . . . . . . . . . . . . .
103
Vine Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .
104
Leaf Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
106
Leaf Area Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
111
Root Weight a Harvest . . . . . . . . . . . . . . .. . . . . . . . . . .
114
Root Length at harvest . . . . . . . . . . . . . . . . . . . . . . . . .
117
Incidence of Insect Pest and Diseases . . . . . . . . . . . . . . . . . .
119
Cutworm Incidence . . . . . . . . . . . . . . . . . . . . . . . . . . .
119
Leaf curling Incidence . . . . . . . . . . . . . . . . . . . . . . . . .
121
Correlation of Morphological, Physiological, Growth,
Incidence of Pest and Diseases and Vine Yield. . . . . . . . . . . .
123
SUMMARY, CONCLUSIONS AND RECOMMENDATIONS. . . . . . 126
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
126
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .
130
Recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
131
LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
135
BIOGRAPHICAL SKETCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
154
Screening And Evaluation Of Sweet potato Genotypes
For Water Stress Resistance /Agnes C. Perey. 2012
Document Outline
- Screening and evaluation of sweetpotatogenotypes for water stress resistance
- BIBLIOGRAPHY
- INTRODUCTION
- REVIEW OF LITERATURE
- MATERIALS AND METHODS
- RESULTS AND DISCUSSION
- SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
- LITERATURE CITED
- APPENDICES