BIBLIOGRAPHY CAMINGAWAN, JOVELYN GUINGABAN....
BIBLIOGRAPHY
CAMINGAWAN, JOVELYN GUINGABAN. MARCH 2012. Characterization of
Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The Weeds
(Galinsogaparviflora and Ageratum conyzoides).Benguet State University, La Trinidad,
Benguet.
Adviser: Asuncion L. Nagpala, Ph.D.
ABSTRACT
The study was conducted at the Plant Pathology Laboratory Department, Benguet State
University, La Trinidad, Benguet from November to February 2012 to characterize the powdery
mildew infecting French bean (Phaseolus vulgaris L.) and the weeds (Galinsogaparviflora and
Ageratum conyzoides) and determine if the same type of powdery mildew infects Bokod variety
and the weeds.
Results revealed that the powdery mildew infecting French bean and Galinsogaparviflora
is close to OidiumpolygoniDC., while powdery mildew infecting Ageratum conyzoidesis close to
Oidiumcichoracearum DC. This indicates that the Galinsogaparviflora is an alternative host of
the powdery mildew (OidiumpolygoniDC.) infecting beans while Ageratum conyzoidesis an
alternative host of OidiumcichoracearumDC.causing powdery mildew of cucurbits.
The following are the characteristics of O.polygoniDC.: conidia measures 16.45-17 µm;
ellipsoidal in shape; hyaline and borne singly; conidiophore on superficial hyphae attached to the
epidermal cell of the host and base of conidiophore not twisted. On the other hand, the
characteristics of the O.cichoracearum DC.are the following: the conidia measures 11.7-12 µm,
ellipsoidal in shape; hyaline and borne in chain;conidiophore on superficial hyphae attached on
host surface and base of the conidiophore is not twisted.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The Weeds
(Galinsogaparviflora and Ageratum conyzoides)/ JovelynGuingabanCamingawan. 2012
Based on the results, O. polygoni DC.andO. cichoracearum DC. differ in the size of
conidia and number of conidia attached to the conidiophore (single or in chain). It was observed
that Oidiumpolygoni DC. hasbigger conidia ranging from 16-17 µm while O. cichoracearum
DC. has a smaller conidia ranging from 11-12 µm.
Since both species of powdery mildew were found associated with G. parvifloraand A.
conyzoides, these weeds should be eradicated if found in fields grown with beans and cucurbits.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The Weeds
(Galinsogaparviflora and Ageratum conyzoides)/ JovelynGuingabanCamingawan. 2012
TABLE OF CONTENTS
Page
Bibliography...…………………………………………………………………….. i
Abstract……………………………………………………………………………. i
Table of Contents…………………………………………………………………. iii
INTRODUCTION………………………………………………………………… 1
REVIEW OF LITERATURE……………………………………………………... 5
MATERIALS AND METHODS…………………………………………………. 14
RESULTS AND DISCUSSION………………………………………………….. 16
Characterization of Powdery Mildew
Infecting French Bean (Bokod variety)
and the Weed Galinsogaparviflora………………………………………. 16
Characterization of Powdery Mildew
Infecting
Ageratum conyzoides………………………………………….... 20
Provisionary Key………………………………………………………….. 24
SUMMARY, CONCLUSION AND RECOMMMENDATION…………………. 25
Summary…………………………………………………………………. 25
Conclusion……………………………………………………………….. 25
Recommendation……………………………………………………….... 26
LITERATURE CITED…………………………………………………………... 27
INTRODUCTION
Powdery mildew has a long history in green house production that contributes to
significant economic losses in many greenhouse floriculture and vegetable crops. It
reduces crop aesthetic and value but do not do not kill the plant. In greenhouses, powdery
mildews usually survive between crops as hyphae or fungal strands in living host plants
or weedy host. Under certain circumstances, some powdery mildew fungi produce small,
black, pepper-like chasmotecia (formerly cleistothecia). These structures allow the
fungus in the absence of the suitable host.However, the role of these resistant structures is
probably insignificant in greenhouse situations since continuous cropping usually
provides a constant source of living host. Powdery mildews are easily recognized by the
white, powdery growth of the fungus on infected portions of the plant host. Colonies vary
in appearance from fluffy and white to sparse and gray. Powdery mildew fungi usually
attack young developing shoots, foliage, stems, and flowers but can also colonize mature
tissues (Douglas, 2008).
Powdery mildew belongs to the kingdom fungi, phylum ascomycota, class
loculoascomycetes, order erysiphales, and genus erysiphe (Quimioet al., 2001).
Powdery mildews are probably the most common, conspicuous, widespread and
easily recognizable plant diseases. The fungi causing powdery mildews are obligate
parasite: they cannot be cultured on artificial nutrient media. They produce mycelium that
grows only on the surface of the plant tissues, never invading the tissues themselves.
They obtain nutrients from the plants by sending haustoria (feeding organs) into the
epidermal cell of the plant organs (Agrios, 1997).
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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Powdery mildew is a common disease on many types of plants. There are many
different species of powdery mildew fungi and each species only attacks specific plants.
A wide variety of vegetable crops are affected by powdery mildews, including beans,
beets, carrot, cucumber, eggplant, lettuce, peas, peppers, radishes, squash, tomatoes, and
turnips. Powdery mildews generally do not require moist conditions to establish and
grow, and normally do well under warm conditions; thus they are more prevalent than
many other leaf-infecting diseases (Davis et al., 2008).
According to (Edmunds and Pottorff, 2009), powdery mildew fungi produce
similar symptoms on plant parts. It is characterized by spots or patches of white to
grayish, talcum-powder-like growth. Tiny, pinhead-sized, spherical fruiting structures
that are first white, later yellow-brown and finally black, may be present singly or in a
group. These are the cleistothecia or overwintering bodies of the fungus. Infected leaves
may become distorted, turn yellow with small patches of green, and fall prematurely and
the infected buds may fail to open.
French beans (Phaseolus vulgaris L.) are fast-growing annuals, and as they
originate from a tropical climate require warm soil in which to germinate and grow. It is
self – pollinating, and generally produces heavy yields, provided that the young beans are
picked regularly and the plants are growing well (Phillips and Martyn, 1993).
According to (Sahadevan, 1987), per 100g edible portion of French beans, it is
composed of 36.0 calories of Food energy, 2.3 g protein, 6.2 g Carbohydrate, 54.0 mg of
Calcium, 6.0 mg Phosphorus, 1.8 mg Iron, 0.1 mg Vitamin B1, 0.2 Vitamin B2 and 15.8
mg Vitamin C.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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Bokod variety (NSIC 2009 BSnBn2) is a selection from an introduced accession
from the International Center for Tropical Agriculture (CIAT) in Cali, Columbia. It has
an average yield of 9.29 t/ ha. It has shorter and tastier straight green pod and is very
much liked by farmers and consumers. It has a comparable moderate resistance to bean
rust and better resistance to weevil, pod borer, stem breakage and lodging. The number of
flower cluster per plant is 9, with 5 pods per cluster. It flowers after 42 days of planting.
The first harvest could be after 50 days and the last harvest is after 74 days. The pod
length is 13.4 cm with 6 seeds per pod that is black in color. Bokod variety could also be
grown in high, mid and low – elevation areas (Tandanget al., 2001) as cited in The
Philippine Journal of Crop Science, December 2010.
According to (Fryer and Makepeace, 1997), weed species are hosts of many
organisms that attack crops, including insects, nematodes, fungi, bacteria and viruses. It
act as sources of infection, or reservoirs which tend to defeat the purpose of crop rotation.
Its chief effect is to decrease yields by depriving the crop from light, water and nutrients
which would otherwise be available to it.
In a survey done at Balili, La Trinidad, Benguet by Balaki in 1981 as cited in the
Weed Control in Tropical crops (Moody, 1986), he reported a total of 56 species under
43 genera and 15 families. The dominant weeds were GalinsogaparvifloraCav., G.
quadriradiataR. & P., Ageratum conyzoidesL., A.
houstonianumMill.,Spilanthesacmella(L.) Murr.,Crassocephalumcrepidioides(Benth) S.
Moore,CommelinabenghalensisL., PortulacaoleraceaL., Oxalis corymbosaDC., and
BedenspilosaL. Although these weeds are mainly observed during the rainy season, their
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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abundance could be in dry seasons due to ambient conditions which favored their
germination.
Considering its economic and nutritional value, French beans are a healthy option
for many health conscious people as they are rich in many vital nutrients that are
considered essential for the proper growth and metabolism of the body. French beans are
filled with healthy dietary fibers that help in the prevention of cholesterol. These fibers
are also beneficial for diabetic people as they help in preventing the sugar levels from
rising up immediately after having a meal. It is also helpful in energizing the body as they
are rich in iron, the nutrients found in hemoglobin which helps in giving energy to the
body. It has many anti-inflammatory nutrients like beta-carotene and, Vitamin C. These
nutrients help in preventing many disease and ailments where there are chances of
inflammation, such as asthma, rheumatoid arthritis and osteoarthritis. They also
contribute in preventing fatal diseases like colon cancer (Anonymous, 2008).
Powdery mildews (Erysiphales) on plant species regarded as weeds are of
potential practical importance because weeds can function as alternative hosts for
powdery mildews affecting crop plants and because some species might have a potential
use for biological control agents against weeds (Dugan and Glawe, 2007).
The study aimed at characterizing the powdery mildew infecting French bean
(Bokod variety) and the weeds (Galinsogaparvifloraand Ageratum conyzoides); and
determine if the same type of powdery mildew infects the Bokod variety and theweeds.
Time and Place of the Study
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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The study was conducted from November 2011 to February 2012 at the the Plant
Pathology Department, Benguet State University La Trinidad, Benguet.
REVIEW OF LITERATURE
The Crop
French beans are half-hardy annuals. There are two types that are available, the
dwarf type and the climbing. Dwarf type is commonly called as ‘bush’ bean or ‘sitting’
beans and the climbing type is commonly called as ‘pole’ beans. French beans are
sometimes known as string beans or kidney beans. It is valuable for their vitamin and
mineral content. It is best grown in a well-drained fertile soil with a soil pH of 6.5 – 7.0
(Biggs, 1994).
According
to
(Kmetijstyo, 2000), beans and pea represent high-protein food of
plant origin. Both plants improve soil as in root nodules nitrogen fixation is done by
bacteria fixing up to 200kg/ha of nitrogen gas from the atmosphere and live in symbiotic
relationship.
Leguminous crop has a high capacity for nitrogen fixation by Rhizobium bacteria
in the root nodule. Nitrogen fixation depends on the efficiency of leaf photosynthesis and
nitrogenase activity (Maiti, 1997).
Neismeth and Hartman (2009), mentioned that bean diseases includes bean yellow
mosaic virus, stem and root rots, Rhizoctonia Root Rot (Rhizoctoniasolani), Fusarium
Root Rot (Fusariumsolanif. phaseoli), Pythium Root Rot (Pythium spp.), Anthracnose
(Colletotrichumlindemuthianum), Bacterial Blights, Common Blight
(Xanthomonasphaseoli), Wilt (Corynebacteriumflaccumfaciens), Halo Blight
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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(Pseudomonas phaseolicola), Brown Spot (Pseudomonas syringae) and Bean Rust
(Uromycesphaseoli).
The Weed
Weeds are like pathogens, pests of crops and some of the worst are parasites
which are closely analogous to some fungal diseases in their mode of attachment to the
host and in the production of phytotoxins. Most weeds have a less close association with
the crop but can cause severe losses by competition for the available nutrients or water in
the soil or for light. A further cause of damage is allelopathy, where toxic exudates from
weeds have an inhibitory effect on crop germination or growth. The overall direct losses
due to weeds are often underestimated as the first 10-20% of crop loss may be
accompanied by no visible damage symptoms. There are also indirect effects of weed
growth which includes effects on crop quality, increased cost of harvesting and influence
on pests and diseases (Waller et al., 2001).
According to (Fryer and Makepeace, 1977), weed vegetation can be useful at
particular times on arable land in preventing soil erosion, preserving soil structure or
regulating fertility. However, if these weeds produce seeds, they can cause trouble in
subsequent crops. On uncultivated lands, weed spp. form a part of a community of
organisms of all kinds and any change in the diversity of the vegetation may have
profound effects on wildlife, for good or ill. Crops that are slow to establish and cover the
ground are particularly susceptible to weed competition. Weed seeds are spread mainly
by man’s activities, especially in inadequately – cleaned crop seed. Farm machinery can
spread weed seeds, either inside it, derived from the crop it was last used for, or in mud
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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on wheels and other parts in contact with soil. It could also be spread by man, birds and
other animals.
Galinsogaparviflora is an herbaceous plant in the Asteraceae (daisy) family. It has
several common names including Guasca (Colombia), Mielcilla (Costa Rica), Galinsoga
(NZ), gallant soldier (USA). It is also known by the taxonomic name Tridaxparviflora.
Galinsogaparviflora was brought from Peru to Kew Gardens in 1796, and later escaped
to the wild in Britain. In Britain its name Galinsoga is sometimes popularly rendered as
"gallant soldiers", and then sometimes altered to "soldiers of the Queen". In Colombia it
is used as a spice herb in the soup Ajiaco. It can also be used as an ingredient in leaf
salads. In much of the world it is considered as a weed but it is extremely effective in
treatment of wounds. Its juice helps blood to coagulate faster and also acts as an
antibiotic agent. Some people claim that usage of Galinsoga helps wounds heal faster.
Even though it is considered a weed, it is an extremely useful herb (Anonymous, 2007).
Nagpalaet al., (2003) reported that Galinsogaparviflora was infected with
powdery mildew but the species was not characterized.
Ageratum conyzoides is also an herbaceous plant in the Asteraceae family. It is
known as Billygoat-weed, Chick weed, Goatweed, Whiteweed; A. conyzoidesL.,
Ageratum obtusifolium Lam., and CacaliamentrastoVell is a native to Tropical America,
especially Brazil. It is an herb which is 0.5–1 m high, with ovate leaves 2–6 cm long, and
the flowers are white to mauve. In Vietnam, the plant is called cứtlợn (Pig Feces) due to
its growth in dirty areas. It has medicinal plant properties. However, it's limited for
external use due to toxicity issues. It is also an insecticide and nematicide.IngestingA.
conyzoides can cause liverlesions and tumors. The plant contains the pyrrolizidine
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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alkaloidslycopsamine and echinatine (Anonymous, 2011).
Similarly, Nagpala et al., (2008) observed that Ageratum conyzoidesgrowing at La
Trinidad Balili Experimental Field were infected with powdery mildew and the causal
pathogen is Oidium sp. The symptom is a powdery white mold that appears on the leaf
surface. Infection starts with the older leaves and progresses to younger ones as the
infection develops and become severe.
A.
conyzoides is prone to becoming a rampant environmental weed when grown
outside of its natural range. It is an invasive weed in Africa, Australia, Southeast Asia and
USA. It is considered a moderate weed of rice cultivation in Asia (Anonymous, 2011).
According to (Iqbalet al., 2004) Ageratum conyzoides L. is an annual herb in the
tropics and subtropics whose extracts are known to possess pharmacological and biocidal
activity. They reported on the bioactivity of a secondary metabolite (a chromene) isolated
from the shoots of A. conyzoides against some plant pathogenic fungi. Organic solvent
extracts from the shoots were tested for antifungal activity against the plant pathogenic
fungi
Rhizoctoniasolani, Sclerotiumrolfsii, Botryodiplodiatheobromae,
Phomopsistheaeand Fusarium species growing in- vitro on potato dextrose agar medium.
The cruden-hexane extract completely inhibited the growth of R. Solaniand S. rolfsii. The
growth of R. solaniand S. rolfsii was completely inhibited by precocene II at a
concentration of 80–100 ppm. The sclerotia of R.solaniand S. rolfsii were also completely
suppressed by 150 ppm of precocene II. Sub-culture of these inhibited fungi onto
precocene II-free medium restored growth of the fungus, indicating that precocene II is
fungistatic. Crude or refined extracts from A. conyzoides offer the possibility of
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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biocontrol of plant pathogenic fungi. Ageratum conyzoides has an antifungal
activity or fungistasis on Rhizoctoniasolaniand Sclerotiumrolfsii.
The Pathogen
Powdery mildew typically begins rapid growth on the lower leaves and sheaths
when plants begin to joint. It is usually favored by temperatures between 10 and 22°C.
The infection and disease development decline when temperatures increase above 25°C.
Conidia are the primary inoculum source for dissemination of the fungus. They are easily
dislodged from lesions by wind and rain. Production of conidia is optimal at 20°C and
declines rapidly above and below that temperature. Although conidia only survive for
several days, they are capable of disseminating the fungus long distances. New pustules
with conidia are produced every seven to ten days at optimal conditions and provide
repeating cycles of spores. Conidia germinate most rapidly at 97 to 100 percent relative
humidity, but their high water content allows them to germinate when humidity declines
below 50 percent. Frequent light rain removes conidia from leaves and thus reduces the
number of new colonies that form. After crop maturity, ascospores in cleistothecia serve
as survival structures, but their role in initiating disease is much less important than that
of the conidia in most environments (Cunfer, 2002).
According to (Quimio and Hanlin, 1999), erysiphales has a septated superficial
mycelium anchored to the epidermal host cells by haustoria. Sexual reproduction is
distinguished by a close ascocarp (cleistothecium) within globose or pyriformasci while
asexual reproduction is by chained conidia on long erect conidiophores.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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Morphological Features Used in Distinguishing
Genera of Erysiphales
Determination of Erysiphales is based on a variety of morphological structures
produced throughout their life cycles. Erysiphales are pleomorphic fungi typically
involving both sexual (teleomorphic) and asexual (anamorphic) states. In most taxa,
hyphae primarily are formed superficially on host tissue. Conidiophores are formed from
superficial mycelia or in taxa with internal mycelia that emerges through stomata or
epidermal cells to produce conidia. Two basic kinds of conidiophores are recognized
(Braun et al., 2002); one kind is conidia matures singly, dehiscing upon maturation at
which time a conidium develops; in the other kind, a series of conidia mature more
gradually, resulting in a chain of conidia exhibiting increasing maturity distal to the
conidiogenous cell. In the absence of disturbance, conidia formed singly may accrue in
false chains. In most taxa, conidia produced from a single conidiophore are
morphologically similar (Glawe, 2006).
Erysiphepolygoni is a widespread and numerous hosts in Rumexand Polygonum.
It was also seen repeatedly on PolygonumaviculareL. (prostrate knotweed) in
Washington and Idaho. E. polygoni mycelia were amphigenous, conidia were (28-) 31-48
(-50) x 13-17 µm, lacked fibrosin bodies and were borne singly on conidiophores (Dugan
and Glawe, 2007). Braun et al., (2002) defined fibrosin bodies as refractive, cytoplasmic
structures that occur within conidia and exhibit varied shapes including comma’s, cones
or rods.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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Salmon (1900) defined E. polygoni DC. broadly to include a wide range of
morphological characters and occur on a number of host families including Apiaceae
(=Umbelliferae), Chenopodiaceaeand Polygonaceae.
Golovinomycescichoracearum
has been reported (as
Erysiphecichoracearum DC)
from Coreopsis species in Europe and New Zealand, as well as from California, Illinois,
Maryland, Minnesota, New York, and Wisconsin. Golovinomycescichoracearum hyphae
were superficial, produced nipple-shaped appressoria, conidiophores with foot cells
measuring 23.0-52.5 × 10.5-13.5 µm, and chains of conidia. Conidia were hyaline, short-
cylindrical to ovoid, lacked fibrosin bodies, and measured 26.5-40.5 × 12.5-18 µm. The
teleomorph included sphaeroidalchasmothecia measuring 125-220 µm with mycelioid
appendages, and multiple short-stipitateasci measuring 49.0-58.0 × 29.5-43.5 µm.
Ascospores were subhyaline to pale yellow, ellipsoid-ovoid, two per ascus, and measured
24.5-31.5 × 16.0-21.0 µm (Glaweet al., 2006).
According to (Braun, 1987) as cited by (Glawe and Duffield, 2007), the powdery
mildew fungus GolovinomycescichoracearumDC. V.P Heluta
(ErysiphecichoracearumDC.) (Erysiphales) occur on a wide range of Asteraceae.
Quimio and Hanlin (1999) in a simple provisionary key to powdery mildew
genera and species based mainly on the anamorphs presented by Boesewinkel (1980) and
von Arx (1987) and similarly with the key presented by Spencer (1978).
ErysiphepolygoniDC.have a conidia borne singly, conidiophore on superficial hyphae,
conidia ellipsoidal, on herbaceous plants. On the other hand,
ErysiphecichoracearumDC.have a conidia in chains, base of conidiophore not swollen
and without fibrosin bodies.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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Management of Powdery Mildew Disease
According to (Davis, 2008) the best method of controlling powdery mildew is
prevention. Planting resistant varieties when available, or avoiding the most susceptible
varieties, and following good cultural practices will adequately control powdery mildew
in many cases. However, very susceptible vegetables such as cucurbits (cucumber,
melons, squash, and pumpkins) may require fungicide treatment. Several least-toxic
fungicides are available but must be applied not later than the first sign of disease. Plant
in sunny areas as much as possible, provide good air circulation, and avoid applying
excess fertilizer. A good alternative is to use a slow-release fertilizer. Overhead
sprinkling may help reduce powdery mildew because spores are washed off the plant.
However, overhead sprinklers are not usually recommended as a control method in
vegetables because their use may contribute to other pest problems. Use least – toxic
fungicides that are available, including horticultural oils, neem oil, jojoba oil, sulfur, and
the biological fungicide Serenade. With the exception of the oils, these materials are
primarily preventive. Oils work best as eradicants but also have some protectant activity.
Sulfur products have been used to manage powdery mildew for centuries but are only
effective when applied before disease symptoms appear. Biological fungicides (such as
Serenade) are commercially available beneficial microorganisms formulated into a
product that, when sprayed on the plant, destroys fungal pathogens. The active ingredient
in Serenade is a bacterium, Bacillus subtilis, that helps prevent the powdery mildew from
infecting the plant. While this product functions to kill the powdery mildew organism and
is nontoxic to people, pets, and beneficial insects, it has not proven to be as effective as
the oils or sulfur in controlling this disease.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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Malinias (2011) found out in her study that 37.50 ml cooking oil mixed with 1
egg yolk blended in 100 ml of water can provide protection against powdery mildew
provided it was applied before the onset of the disease. The COY mixture (cooking oil
plus egg yolk) was added in distilled water to bring 20L spray solution. Cooking oil and
yolk mixture can be used as an alternative for fungicide because it is effective and simply
prepared. It is edible and environment, thus recommended for organic production. Weed
control are widely practiced in developing countries where herbicides are not available or
beyond resources of the farmers. It is the preferred methods in organic agriculture.
Cultural methods includes sowing of clean seed, avoiding introduction of weeds through
manure, fodder, soil on transplanted crop plants and contaminated equipment or irrigation
water. Immediate planting after preparation of seed bed reduces early competition from
weeds. Crop rotation can be manipulated to prevent or avoid the build- up of weed
problems. Physical methods include primary and secondary tillage, cutting of weeds,
hand pulling or rouging which is laborious, and flooding. Biological control includes
mycoherbicides particularly for perennial aquatic and rangeland species. Chemical
control generally involves use of different herbicides (Waller et al., 2001).
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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MATERIALS AND METHODS
Collection of Specimens
Beans from the Bokod variety (NSIC 2009 BSnBn2) and the weeds
Galinsogaparviflora and Ageratum Conyzoidesinfected with powdery mildew were
collected from the Organic farm at Balili, La Trinidad, Benguet. These specimens were
brought in the laboratory for microscopic observation.
Preparation of Mounts and Characterization
of Powdery Mildew
The symptoms of powdery mildew were described based on its appearance on the
actual specimens. The mounts were prepared through thin tissue sectioning and simple
scraping. The structures were morphologically characterized based on its structure on the
temporary and permanent mounts prepared and observed under the microscope.
Characterization was done using the illustrated genera of plant pathogenic fungi in tropics
(Quimio and Hanlin 1999) and the powdery mildews (Spencer, 1987) based on the
following criteria: size and shape of the conidia, color of the conidia, number of conidia
(borne singly or in chain), base of the conidiophore and mode of attachment of the
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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conidia from the conidiophores. The conidial measurement was done by the use of an
ocular micrometer. There were 20 conidia measured in each specimen and the average
mean was obtained.
Measurement of Conidia
The conidia were measured exactly with the use of a calibrated microscope. The
ocular micrometer was inserted in the eyepiece of the microscope and the mounts of
conidia were placed on the stage of the microscope. Focusing was done at the lower
power objective (LPO) and shifting to the high power objective (HPO). The ocular
divisions were counted from 0 µm – 100 µm as cited by Esiong (2004).
Data Gathered
1. Shape of the conidia. The observations were done based on the appearance of the
conidia on the focused specimens under the microscope. It was characterized whether
pointed, barrel-shaped or ellipsoidal.
2. Color of the conidia. The observations were done based on the appearance of the
conidia on the focused specimens under the microscope. It was characterized whether it is
hyaline, light to dark brown and others.
3. Size of the conidia. A total of twenty conidia were measured using the ocular
micrometer inserted on the eyepiece of the microscope. The total mean was obtained after
the measurement.
4. Number of conidia. The observations were done based on the appearance of the
conidia on the focused specimens under the microscope. It was characterized whether the
conidia was borne singly or in chains.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
16
5. Base of the conidiophore. The observations were done based on the appearance
of the base of the conidiophore on the focused specimens under the microscope. It was
characterized whether it is twisted or not.
6. The manner of attachment of the conidiophores to the host cell. The observations
were done based on where the conidiophore was attached on the focused specimens
under the microscope; whether it is attached on the epidermal host cell or arises from the
stomata.
RESULTS AND DISCUSSION
Characterization of Powdery
Mildew Infecting French Bean
and the Weed Galinsogaparviflora
The powdery mildew infecting French bean (Bokod variety) and the weed
Galinsogaparviflora was characterized as follows (Table 1).
Table 1. Characteristics of powdery mildew infecting French bean and Galinsoga
parviflora
CRITERIA
FRENCH BEAN (BOKOD VARIETY)
AND THE WEED G. parviflora
Size of Conidia
16.45 to 17 µm
Shape of Conidia
Ellipsoidal
Color of Conidia
Hyaline
Number of Conidia Attached to
Conidia borne singly
Conidiophore
Base of the Conidiophore
Not twisted
Attachment of Conidiophore to
On host epidermal cells
the Host
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
17
Table 2 below shows the size of the measured conidia of
OidiumpolygoniDC.infecting French bean (Bokod variety) and the weed G. parviflora.
Based from the result, most of the conidia of O. polygoniDC.on the Bokod
varietymeasured 16 µm to 17 µm but some measured 15 to 18 µm (Figure 1b-c).
On the other hand, O. polygoniDC.onG. parviflora has a conidia 13, 14, 15, 18,
19 and 22 µm; although the dominant size is 16 µm (Figure 2c).
The size of the conidia measured in the study is close to the 15 µm size of conidia
as cited by Dugan and Glawe (2007) (Figure 3a-b).
Table 2. Number and size of measured conidia (µm) of powdery mildew infecting French
bean (Bokod variety) and the weed G. parviflora
NUMBER OF CONIDIA
SIZE (µm)
MEASURED
FRENCH BEAN (BOKOD
G. parviflora
VARIETY)
1 16
19
2 17
16
3 18
13
4 17
17
5 17
17
6 16
17
7
17
14
8 18
15
9 16
14
10 18
18
11 16
19
12 16
17
13 16
16
14 16
22
15 16
15
16 16
14
17 16
19
18 16
17
19 16
14
20 15
15
MEAN 16.45
16.4
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
18
17 µm
16 µm
a
b
c
Figure 1a. Powdery mildew on French bean (Bokod variety)
b-c. Conidia of OidiumpolygoniDC. (16.45-17 µm) at 400x;
b
a
16 µm
17 µm
c
d
Figure 2a-b. Stems and leaves of G. parviflorainfected with
powdery mildew as shown by circle and arrow
c-d. Conidia and size (16,17 µm) of O. polygoniDC.
infectingG. parviflora (400x)
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
19
a
b
15 µm
Figure 3a. Conidia attached to Conidiophore as
indicated by arrow (Pantaky, 2010)
b. Conidia of O. polygoniDC. (15 µm)
by (Dugan and Glawe,2007)
Shape of the conidia.Based on microscopic observation, the conidia of
Oidiumpolygoni DC.areellipsoidal and hyaline as shown in Figure 4.
Figure 4.Single, ellipsoidal conidia of O.
polygoniDC. attached to
conidiophore as indicated by arrow
(400x)
Base of conidiophore. It was observed that the base of conidiophore of O.
polygoni DC.was not twisted (Figure 5).
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
20
Figure 5.Conidia of O. polygoniDC.attached
to the Conidiophore as indicated by
arrow(400x)
Mode of attachment of the conidiophore to the host cell. It was observedthat the
conidiophore of the powdery from French bean (Bokod variety) and G. parviflorawas
anchored to the epidermal cell of the host or it has a superficial mycelia attached to the
host cell. The conidiophore is septated (Figure 6).
a
b
Figure 6 a. Conidiophore bearing the conidia of O. polygoniDC. attached to the host
cell (400x); b. Conidia borne singly and detaches as it matures as shown by
arrow
(400x)
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
21
Characterization of Powdery Mildew
Infecting Ageratum conyzoides
The powdery mildew infecting Ageratum conyzoideswas characterized as follows
(Table 3.)
Table 3. Characteristics of powdery mildew infecting the weed Ageratum conyzoides
CRITERIA
Ageratum conyzoides
Size of Conidia
16.45o 17 µm
Shape of Conidia
Ellipsoidal
Color of Conidia
Hyaline
Number of Conidia Attached to
Conidia borne singly
Conidiophore
Base of the Conidiophore
Not twisted
Attachment of Conidiophore to the Host
On host epidermal cells
This result was corroborated by (Quimio and Hanlin, 1990); (Dugan and Glawe,
2007) and (Spencer, 1987).
Table 4 below shows the size of the measured conidia from the powdery mildew
infected leaves of A. conyzoides. Based the result, most of the conidia
Oidiumcichoracearum DC.measured 11,12 and 13µm. The most dominant size is 11 µm
(Figure 7).
The size of the conidia measured in the study is close to the 12.5-18 µm size of
conidia of O. cichoracearumDC. cited by (Glaweet al., 2006) as shown in Figure 7e.
Table 4.Number and size of measured conidia (µm) of powdery mildew on the weed A.
conyzoides
NUMBER OF THE CONIDIA MEASURED
SIZE (µm)
1
12
2 11
3 11
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
22
4 11
5 11
6 11
7
12
8 13
9 12
10 11
11 12
12 12
13 13
14 12
15 11
16 12
17 11
18 12
19 13
20 11
MEAN 11.7
b
a
Figure 7 a-b. Powdery mildew on A. conyzoides
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
11 µm
23
11 µm
a
b
c 12.5 µm
Figure 7 c-d. Conidia of Oidiumcichoracearum (400x)
e. Conidia attached to conidiophore (Glaweet al., 2006)
Shape of conidia. Based on microscopic observation, the conidia of
OidiumcichoracearumDC. are ellipsoidal and hyaline (Figure 8).
Figure 8. Ellipsoidal conidia in chain as indicated
by arrow(400x)
Base of conidiophore. It was observed that the base of the conidiophore was not
twisted (Figure 9a-b).
Mode of attachment of the conidiophore to the host cell. It was observed that the
conidiophore of the powdery from Ageratum was anchored to the epidermal cell of the
host. The conidiophore is septated (Figure 9a-b).
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
24
Figure 9a-b. Conidia borne in chain attached to the conidiophore that is anchored to
the host cell as indicated by arrow.
Provisionary Key. Below is a simple provisionary key to separate powdery
mildew genera on French bean (Bokod variety), Galinsogaparvifloraand A.
conyzoidesusing the taxonomic referred of Quimio and Hanlin(1999), Dugan and
Glawe(2007) and Spencer 1987
Conidia borne singly
Conidiophore on superficial hyphae
Base of conidiophore not twisted
Conidial size ranges from 16-17 µm,
Conidia ellipsoidal
On herbaceous plants…………………………Oidiumpoygoni DC.
On weeds under Asteraceae family………….OidiumpolygoniDC.
Conidia borne in chain
Conidiophore on superficial hyphae
Base of conidiophore not twisted
Conidial size ranges from 11-12 µm
Conidia
ellipsoidal
on
herbaceous
plants…….(OidiumcichoracearumDC.)
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
25
SUMMARY, CONCLUSION AND RECOMMENDATION
Summary
This study aimed to characterize the powdery mildew on French bean (Bokod
variety) and the weeds (Galinsogaparvifloraand Ageratum conyzoides) and determine if
the same type of powdery mildew infects the Bokod variety grown at BSU Experiment
Station; organic farm and the weeds associated with the crop. Characterization of the
powdery mildew was done by microscopic observation.
Results of the study revealed that the Oidiumpolygoni DC. was the type of
powdery mildew that infects both the French bean (Bokod variety) and the weed
Galinsogaparviflora while Oidiumcichoracearum DC. infects the weed Ageratum
conyzoides.
The characteristics of Oidiumpolygoni DC.were based on the observation using
the taxonomic key of Quimio and Hanlin, 1999; Dugan and Glawe, 2007 and Spencer
1987. The characteristics of OidiumpolygoniDC.includes a conidia that is 16.45-17 µm,
ellipsoidal in shape; hyaline and borne singly; conidiophore on superficial hyphae
attached to the epidermal cell of the host and base of conidiophore not twisted. On the
other hand, the characteristics of the O. cichoracearum DC.are the following: the conidia
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
26
measures 11.7-12 µm, ellipsoidal in shape; hyaline and borne in chain; conidiophore on
superficial hyphae attached on host surface and base of the conidiophore is not twisted.
Conclusion
Based on the results, O.polygoni DC.andO.cichoracearum DC. differ in the size
of conidia and number of conidia attached to the conidiophore (single or in chain). It was
observed that O.polygoni DC. has bigger conidia ranging from 16-17 µm while O.
cichoracearum DC. has a conidia whose size range from 11-12 µm.
Recommendation
In relation to disease management, it is recommended to eradicate the weed
Galinsoga and Ageratum in the field and greenhouse especially when the crops grown are
legumes which include peas, beans and cucurbits. Both harbor the powdery mildew
O.polygoniDC and O. cichoracearumDC.These fungi serve as sources of inoculum for
infection of legumes and cucurbits. In addition, these weeds must be disposed properly.
It is further recommended that studies be conducted on the characterization and
identification other weeds serving as alternative host of powdery mildew diseases.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
27
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Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
CAMINGAWAN, JOVELYN GUINGABAN. MARCH 2012. Characterization of
Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The Weeds
(Galinsogaparviflora and Ageratum conyzoides).Benguet State University, La Trinidad,
Benguet.
Adviser: Asuncion L. Nagpala, Ph.D.
ABSTRACT
The study was conducted at the Plant Pathology Laboratory Department, Benguet State
University, La Trinidad, Benguet from November to February 2012 to characterize the powdery
mildew infecting French bean (Phaseolus vulgaris L.) and the weeds (Galinsogaparviflora and
Ageratum conyzoides) and determine if the same type of powdery mildew infects Bokod variety
and the weeds.
Results revealed that the powdery mildew infecting French bean and Galinsogaparviflora
is close to OidiumpolygoniDC., while powdery mildew infecting Ageratum conyzoidesis close to
Oidiumcichoracearum DC. This indicates that the Galinsogaparviflora is an alternative host of
the powdery mildew (OidiumpolygoniDC.) infecting beans while Ageratum conyzoidesis an
alternative host of OidiumcichoracearumDC.causing powdery mildew of cucurbits.
The following are the characteristics of O.polygoniDC.: conidia measures 16.45-17 µm;
ellipsoidal in shape; hyaline and borne singly; conidiophore on superficial hyphae attached to the
epidermal cell of the host and base of conidiophore not twisted. On the other hand, the
characteristics of the O.cichoracearum DC.are the following: the conidia measures 11.7-12 µm,
ellipsoidal in shape; hyaline and borne in chain;conidiophore on superficial hyphae attached on
host surface and base of the conidiophore is not twisted.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The Weeds
(Galinsogaparviflora and Ageratum conyzoides)/ JovelynGuingabanCamingawan. 2012
Based on the results, O. polygoni DC.andO. cichoracearum DC. differ in the size of
conidia and number of conidia attached to the conidiophore (single or in chain). It was observed
that Oidiumpolygoni DC. hasbigger conidia ranging from 16-17 µm while O. cichoracearum
DC. has a smaller conidia ranging from 11-12 µm.
Since both species of powdery mildew were found associated with G. parvifloraand A.
conyzoides, these weeds should be eradicated if found in fields grown with beans and cucurbits.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The Weeds
(Galinsogaparviflora and Ageratum conyzoides)/ JovelynGuingabanCamingawan. 2012
TABLE OF CONTENTS
Page
Bibliography...…………………………………………………………………….. i
Abstract……………………………………………………………………………. i
Table of Contents…………………………………………………………………. iii
INTRODUCTION………………………………………………………………… 1
REVIEW OF LITERATURE……………………………………………………... 5
MATERIALS AND METHODS…………………………………………………. 14
RESULTS AND DISCUSSION………………………………………………….. 16
Characterization of Powdery Mildew
Infecting French Bean (Bokod variety)
and the Weed Galinsogaparviflora………………………………………. 16
Characterization of Powdery Mildew
Infecting
Ageratum conyzoides………………………………………….... 20
Provisionary Key………………………………………………………….. 24
SUMMARY, CONCLUSION AND RECOMMMENDATION…………………. 25
Summary…………………………………………………………………. 25
Conclusion……………………………………………………………….. 25
Recommendation……………………………………………………….... 26
LITERATURE CITED…………………………………………………………... 27
INTRODUCTION
Powdery mildew has a long history in green house production that contributes to
significant economic losses in many greenhouse floriculture and vegetable crops. It
reduces crop aesthetic and value but do not do not kill the plant. In greenhouses, powdery
mildews usually survive between crops as hyphae or fungal strands in living host plants
or weedy host. Under certain circumstances, some powdery mildew fungi produce small,
black, pepper-like chasmotecia (formerly cleistothecia). These structures allow the
fungus in the absence of the suitable host.However, the role of these resistant structures is
probably insignificant in greenhouse situations since continuous cropping usually
provides a constant source of living host. Powdery mildews are easily recognized by the
white, powdery growth of the fungus on infected portions of the plant host. Colonies vary
in appearance from fluffy and white to sparse and gray. Powdery mildew fungi usually
attack young developing shoots, foliage, stems, and flowers but can also colonize mature
tissues (Douglas, 2008).
Powdery mildew belongs to the kingdom fungi, phylum ascomycota, class
loculoascomycetes, order erysiphales, and genus erysiphe (Quimioet al., 2001).
Powdery mildews are probably the most common, conspicuous, widespread and
easily recognizable plant diseases. The fungi causing powdery mildews are obligate
parasite: they cannot be cultured on artificial nutrient media. They produce mycelium that
grows only on the surface of the plant tissues, never invading the tissues themselves.
They obtain nutrients from the plants by sending haustoria (feeding organs) into the
epidermal cell of the plant organs (Agrios, 1997).
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
2
Powdery mildew is a common disease on many types of plants. There are many
different species of powdery mildew fungi and each species only attacks specific plants.
A wide variety of vegetable crops are affected by powdery mildews, including beans,
beets, carrot, cucumber, eggplant, lettuce, peas, peppers, radishes, squash, tomatoes, and
turnips. Powdery mildews generally do not require moist conditions to establish and
grow, and normally do well under warm conditions; thus they are more prevalent than
many other leaf-infecting diseases (Davis et al., 2008).
According to (Edmunds and Pottorff, 2009), powdery mildew fungi produce
similar symptoms on plant parts. It is characterized by spots or patches of white to
grayish, talcum-powder-like growth. Tiny, pinhead-sized, spherical fruiting structures
that are first white, later yellow-brown and finally black, may be present singly or in a
group. These are the cleistothecia or overwintering bodies of the fungus. Infected leaves
may become distorted, turn yellow with small patches of green, and fall prematurely and
the infected buds may fail to open.
French beans (Phaseolus vulgaris L.) are fast-growing annuals, and as they
originate from a tropical climate require warm soil in which to germinate and grow. It is
self – pollinating, and generally produces heavy yields, provided that the young beans are
picked regularly and the plants are growing well (Phillips and Martyn, 1993).
According to (Sahadevan, 1987), per 100g edible portion of French beans, it is
composed of 36.0 calories of Food energy, 2.3 g protein, 6.2 g Carbohydrate, 54.0 mg of
Calcium, 6.0 mg Phosphorus, 1.8 mg Iron, 0.1 mg Vitamin B1, 0.2 Vitamin B2 and 15.8
mg Vitamin C.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
3
Bokod variety (NSIC 2009 BSnBn2) is a selection from an introduced accession
from the International Center for Tropical Agriculture (CIAT) in Cali, Columbia. It has
an average yield of 9.29 t/ ha. It has shorter and tastier straight green pod and is very
much liked by farmers and consumers. It has a comparable moderate resistance to bean
rust and better resistance to weevil, pod borer, stem breakage and lodging. The number of
flower cluster per plant is 9, with 5 pods per cluster. It flowers after 42 days of planting.
The first harvest could be after 50 days and the last harvest is after 74 days. The pod
length is 13.4 cm with 6 seeds per pod that is black in color. Bokod variety could also be
grown in high, mid and low – elevation areas (Tandanget al., 2001) as cited in The
Philippine Journal of Crop Science, December 2010.
According to (Fryer and Makepeace, 1997), weed species are hosts of many
organisms that attack crops, including insects, nematodes, fungi, bacteria and viruses. It
act as sources of infection, or reservoirs which tend to defeat the purpose of crop rotation.
Its chief effect is to decrease yields by depriving the crop from light, water and nutrients
which would otherwise be available to it.
In a survey done at Balili, La Trinidad, Benguet by Balaki in 1981 as cited in the
Weed Control in Tropical crops (Moody, 1986), he reported a total of 56 species under
43 genera and 15 families. The dominant weeds were GalinsogaparvifloraCav., G.
quadriradiataR. & P., Ageratum conyzoidesL., A.
houstonianumMill.,Spilanthesacmella(L.) Murr.,Crassocephalumcrepidioides(Benth) S.
Moore,CommelinabenghalensisL., PortulacaoleraceaL., Oxalis corymbosaDC., and
BedenspilosaL. Although these weeds are mainly observed during the rainy season, their
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
4
abundance could be in dry seasons due to ambient conditions which favored their
germination.
Considering its economic and nutritional value, French beans are a healthy option
for many health conscious people as they are rich in many vital nutrients that are
considered essential for the proper growth and metabolism of the body. French beans are
filled with healthy dietary fibers that help in the prevention of cholesterol. These fibers
are also beneficial for diabetic people as they help in preventing the sugar levels from
rising up immediately after having a meal. It is also helpful in energizing the body as they
are rich in iron, the nutrients found in hemoglobin which helps in giving energy to the
body. It has many anti-inflammatory nutrients like beta-carotene and, Vitamin C. These
nutrients help in preventing many disease and ailments where there are chances of
inflammation, such as asthma, rheumatoid arthritis and osteoarthritis. They also
contribute in preventing fatal diseases like colon cancer (Anonymous, 2008).
Powdery mildews (Erysiphales) on plant species regarded as weeds are of
potential practical importance because weeds can function as alternative hosts for
powdery mildews affecting crop plants and because some species might have a potential
use for biological control agents against weeds (Dugan and Glawe, 2007).
The study aimed at characterizing the powdery mildew infecting French bean
(Bokod variety) and the weeds (Galinsogaparvifloraand Ageratum conyzoides); and
determine if the same type of powdery mildew infects the Bokod variety and theweeds.
Time and Place of the Study
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
5
The study was conducted from November 2011 to February 2012 at the the Plant
Pathology Department, Benguet State University La Trinidad, Benguet.
REVIEW OF LITERATURE
The Crop
French beans are half-hardy annuals. There are two types that are available, the
dwarf type and the climbing. Dwarf type is commonly called as ‘bush’ bean or ‘sitting’
beans and the climbing type is commonly called as ‘pole’ beans. French beans are
sometimes known as string beans or kidney beans. It is valuable for their vitamin and
mineral content. It is best grown in a well-drained fertile soil with a soil pH of 6.5 – 7.0
(Biggs, 1994).
According
to
(Kmetijstyo, 2000), beans and pea represent high-protein food of
plant origin. Both plants improve soil as in root nodules nitrogen fixation is done by
bacteria fixing up to 200kg/ha of nitrogen gas from the atmosphere and live in symbiotic
relationship.
Leguminous crop has a high capacity for nitrogen fixation by Rhizobium bacteria
in the root nodule. Nitrogen fixation depends on the efficiency of leaf photosynthesis and
nitrogenase activity (Maiti, 1997).
Neismeth and Hartman (2009), mentioned that bean diseases includes bean yellow
mosaic virus, stem and root rots, Rhizoctonia Root Rot (Rhizoctoniasolani), Fusarium
Root Rot (Fusariumsolanif. phaseoli), Pythium Root Rot (Pythium spp.), Anthracnose
(Colletotrichumlindemuthianum), Bacterial Blights, Common Blight
(Xanthomonasphaseoli), Wilt (Corynebacteriumflaccumfaciens), Halo Blight
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
6
(Pseudomonas phaseolicola), Brown Spot (Pseudomonas syringae) and Bean Rust
(Uromycesphaseoli).
The Weed
Weeds are like pathogens, pests of crops and some of the worst are parasites
which are closely analogous to some fungal diseases in their mode of attachment to the
host and in the production of phytotoxins. Most weeds have a less close association with
the crop but can cause severe losses by competition for the available nutrients or water in
the soil or for light. A further cause of damage is allelopathy, where toxic exudates from
weeds have an inhibitory effect on crop germination or growth. The overall direct losses
due to weeds are often underestimated as the first 10-20% of crop loss may be
accompanied by no visible damage symptoms. There are also indirect effects of weed
growth which includes effects on crop quality, increased cost of harvesting and influence
on pests and diseases (Waller et al., 2001).
According to (Fryer and Makepeace, 1977), weed vegetation can be useful at
particular times on arable land in preventing soil erosion, preserving soil structure or
regulating fertility. However, if these weeds produce seeds, they can cause trouble in
subsequent crops. On uncultivated lands, weed spp. form a part of a community of
organisms of all kinds and any change in the diversity of the vegetation may have
profound effects on wildlife, for good or ill. Crops that are slow to establish and cover the
ground are particularly susceptible to weed competition. Weed seeds are spread mainly
by man’s activities, especially in inadequately – cleaned crop seed. Farm machinery can
spread weed seeds, either inside it, derived from the crop it was last used for, or in mud
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
7
on wheels and other parts in contact with soil. It could also be spread by man, birds and
other animals.
Galinsogaparviflora is an herbaceous plant in the Asteraceae (daisy) family. It has
several common names including Guasca (Colombia), Mielcilla (Costa Rica), Galinsoga
(NZ), gallant soldier (USA). It is also known by the taxonomic name Tridaxparviflora.
Galinsogaparviflora was brought from Peru to Kew Gardens in 1796, and later escaped
to the wild in Britain. In Britain its name Galinsoga is sometimes popularly rendered as
"gallant soldiers", and then sometimes altered to "soldiers of the Queen". In Colombia it
is used as a spice herb in the soup Ajiaco. It can also be used as an ingredient in leaf
salads. In much of the world it is considered as a weed but it is extremely effective in
treatment of wounds. Its juice helps blood to coagulate faster and also acts as an
antibiotic agent. Some people claim that usage of Galinsoga helps wounds heal faster.
Even though it is considered a weed, it is an extremely useful herb (Anonymous, 2007).
Nagpalaet al., (2003) reported that Galinsogaparviflora was infected with
powdery mildew but the species was not characterized.
Ageratum conyzoides is also an herbaceous plant in the Asteraceae family. It is
known as Billygoat-weed, Chick weed, Goatweed, Whiteweed; A. conyzoidesL.,
Ageratum obtusifolium Lam., and CacaliamentrastoVell is a native to Tropical America,
especially Brazil. It is an herb which is 0.5–1 m high, with ovate leaves 2–6 cm long, and
the flowers are white to mauve. In Vietnam, the plant is called cứtlợn (Pig Feces) due to
its growth in dirty areas. It has medicinal plant properties. However, it's limited for
external use due to toxicity issues. It is also an insecticide and nematicide.IngestingA.
conyzoides can cause liverlesions and tumors. The plant contains the pyrrolizidine
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
8
alkaloidslycopsamine and echinatine (Anonymous, 2011).
Similarly, Nagpala et al., (2008) observed that Ageratum conyzoidesgrowing at La
Trinidad Balili Experimental Field were infected with powdery mildew and the causal
pathogen is Oidium sp. The symptom is a powdery white mold that appears on the leaf
surface. Infection starts with the older leaves and progresses to younger ones as the
infection develops and become severe.
A.
conyzoides is prone to becoming a rampant environmental weed when grown
outside of its natural range. It is an invasive weed in Africa, Australia, Southeast Asia and
USA. It is considered a moderate weed of rice cultivation in Asia (Anonymous, 2011).
According to (Iqbalet al., 2004) Ageratum conyzoides L. is an annual herb in the
tropics and subtropics whose extracts are known to possess pharmacological and biocidal
activity. They reported on the bioactivity of a secondary metabolite (a chromene) isolated
from the shoots of A. conyzoides against some plant pathogenic fungi. Organic solvent
extracts from the shoots were tested for antifungal activity against the plant pathogenic
fungi
Rhizoctoniasolani, Sclerotiumrolfsii, Botryodiplodiatheobromae,
Phomopsistheaeand Fusarium species growing in- vitro on potato dextrose agar medium.
The cruden-hexane extract completely inhibited the growth of R. Solaniand S. rolfsii. The
growth of R. solaniand S. rolfsii was completely inhibited by precocene II at a
concentration of 80–100 ppm. The sclerotia of R.solaniand S. rolfsii were also completely
suppressed by 150 ppm of precocene II. Sub-culture of these inhibited fungi onto
precocene II-free medium restored growth of the fungus, indicating that precocene II is
fungistatic. Crude or refined extracts from A. conyzoides offer the possibility of
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
9
biocontrol of plant pathogenic fungi. Ageratum conyzoides has an antifungal
activity or fungistasis on Rhizoctoniasolaniand Sclerotiumrolfsii.
The Pathogen
Powdery mildew typically begins rapid growth on the lower leaves and sheaths
when plants begin to joint. It is usually favored by temperatures between 10 and 22°C.
The infection and disease development decline when temperatures increase above 25°C.
Conidia are the primary inoculum source for dissemination of the fungus. They are easily
dislodged from lesions by wind and rain. Production of conidia is optimal at 20°C and
declines rapidly above and below that temperature. Although conidia only survive for
several days, they are capable of disseminating the fungus long distances. New pustules
with conidia are produced every seven to ten days at optimal conditions and provide
repeating cycles of spores. Conidia germinate most rapidly at 97 to 100 percent relative
humidity, but their high water content allows them to germinate when humidity declines
below 50 percent. Frequent light rain removes conidia from leaves and thus reduces the
number of new colonies that form. After crop maturity, ascospores in cleistothecia serve
as survival structures, but their role in initiating disease is much less important than that
of the conidia in most environments (Cunfer, 2002).
According to (Quimio and Hanlin, 1999), erysiphales has a septated superficial
mycelium anchored to the epidermal host cells by haustoria. Sexual reproduction is
distinguished by a close ascocarp (cleistothecium) within globose or pyriformasci while
asexual reproduction is by chained conidia on long erect conidiophores.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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Morphological Features Used in Distinguishing
Genera of Erysiphales
Determination of Erysiphales is based on a variety of morphological structures
produced throughout their life cycles. Erysiphales are pleomorphic fungi typically
involving both sexual (teleomorphic) and asexual (anamorphic) states. In most taxa,
hyphae primarily are formed superficially on host tissue. Conidiophores are formed from
superficial mycelia or in taxa with internal mycelia that emerges through stomata or
epidermal cells to produce conidia. Two basic kinds of conidiophores are recognized
(Braun et al., 2002); one kind is conidia matures singly, dehiscing upon maturation at
which time a conidium develops; in the other kind, a series of conidia mature more
gradually, resulting in a chain of conidia exhibiting increasing maturity distal to the
conidiogenous cell. In the absence of disturbance, conidia formed singly may accrue in
false chains. In most taxa, conidia produced from a single conidiophore are
morphologically similar (Glawe, 2006).
Erysiphepolygoni is a widespread and numerous hosts in Rumexand Polygonum.
It was also seen repeatedly on PolygonumaviculareL. (prostrate knotweed) in
Washington and Idaho. E. polygoni mycelia were amphigenous, conidia were (28-) 31-48
(-50) x 13-17 µm, lacked fibrosin bodies and were borne singly on conidiophores (Dugan
and Glawe, 2007). Braun et al., (2002) defined fibrosin bodies as refractive, cytoplasmic
structures that occur within conidia and exhibit varied shapes including comma’s, cones
or rods.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
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Salmon (1900) defined E. polygoni DC. broadly to include a wide range of
morphological characters and occur on a number of host families including Apiaceae
(=Umbelliferae), Chenopodiaceaeand Polygonaceae.
Golovinomycescichoracearum
has been reported (as
Erysiphecichoracearum DC)
from Coreopsis species in Europe and New Zealand, as well as from California, Illinois,
Maryland, Minnesota, New York, and Wisconsin. Golovinomycescichoracearum hyphae
were superficial, produced nipple-shaped appressoria, conidiophores with foot cells
measuring 23.0-52.5 × 10.5-13.5 µm, and chains of conidia. Conidia were hyaline, short-
cylindrical to ovoid, lacked fibrosin bodies, and measured 26.5-40.5 × 12.5-18 µm. The
teleomorph included sphaeroidalchasmothecia measuring 125-220 µm with mycelioid
appendages, and multiple short-stipitateasci measuring 49.0-58.0 × 29.5-43.5 µm.
Ascospores were subhyaline to pale yellow, ellipsoid-ovoid, two per ascus, and measured
24.5-31.5 × 16.0-21.0 µm (Glaweet al., 2006).
According to (Braun, 1987) as cited by (Glawe and Duffield, 2007), the powdery
mildew fungus GolovinomycescichoracearumDC. V.P Heluta
(ErysiphecichoracearumDC.) (Erysiphales) occur on a wide range of Asteraceae.
Quimio and Hanlin (1999) in a simple provisionary key to powdery mildew
genera and species based mainly on the anamorphs presented by Boesewinkel (1980) and
von Arx (1987) and similarly with the key presented by Spencer (1978).
ErysiphepolygoniDC.have a conidia borne singly, conidiophore on superficial hyphae,
conidia ellipsoidal, on herbaceous plants. On the other hand,
ErysiphecichoracearumDC.have a conidia in chains, base of conidiophore not swollen
and without fibrosin bodies.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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Management of Powdery Mildew Disease
According to (Davis, 2008) the best method of controlling powdery mildew is
prevention. Planting resistant varieties when available, or avoiding the most susceptible
varieties, and following good cultural practices will adequately control powdery mildew
in many cases. However, very susceptible vegetables such as cucurbits (cucumber,
melons, squash, and pumpkins) may require fungicide treatment. Several least-toxic
fungicides are available but must be applied not later than the first sign of disease. Plant
in sunny areas as much as possible, provide good air circulation, and avoid applying
excess fertilizer. A good alternative is to use a slow-release fertilizer. Overhead
sprinkling may help reduce powdery mildew because spores are washed off the plant.
However, overhead sprinklers are not usually recommended as a control method in
vegetables because their use may contribute to other pest problems. Use least – toxic
fungicides that are available, including horticultural oils, neem oil, jojoba oil, sulfur, and
the biological fungicide Serenade. With the exception of the oils, these materials are
primarily preventive. Oils work best as eradicants but also have some protectant activity.
Sulfur products have been used to manage powdery mildew for centuries but are only
effective when applied before disease symptoms appear. Biological fungicides (such as
Serenade) are commercially available beneficial microorganisms formulated into a
product that, when sprayed on the plant, destroys fungal pathogens. The active ingredient
in Serenade is a bacterium, Bacillus subtilis, that helps prevent the powdery mildew from
infecting the plant. While this product functions to kill the powdery mildew organism and
is nontoxic to people, pets, and beneficial insects, it has not proven to be as effective as
the oils or sulfur in controlling this disease.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
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Malinias (2011) found out in her study that 37.50 ml cooking oil mixed with 1
egg yolk blended in 100 ml of water can provide protection against powdery mildew
provided it was applied before the onset of the disease. The COY mixture (cooking oil
plus egg yolk) was added in distilled water to bring 20L spray solution. Cooking oil and
yolk mixture can be used as an alternative for fungicide because it is effective and simply
prepared. It is edible and environment, thus recommended for organic production. Weed
control are widely practiced in developing countries where herbicides are not available or
beyond resources of the farmers. It is the preferred methods in organic agriculture.
Cultural methods includes sowing of clean seed, avoiding introduction of weeds through
manure, fodder, soil on transplanted crop plants and contaminated equipment or irrigation
water. Immediate planting after preparation of seed bed reduces early competition from
weeds. Crop rotation can be manipulated to prevent or avoid the build- up of weed
problems. Physical methods include primary and secondary tillage, cutting of weeds,
hand pulling or rouging which is laborious, and flooding. Biological control includes
mycoherbicides particularly for perennial aquatic and rangeland species. Chemical
control generally involves use of different herbicides (Waller et al., 2001).
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
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MATERIALS AND METHODS
Collection of Specimens
Beans from the Bokod variety (NSIC 2009 BSnBn2) and the weeds
Galinsogaparviflora and Ageratum Conyzoidesinfected with powdery mildew were
collected from the Organic farm at Balili, La Trinidad, Benguet. These specimens were
brought in the laboratory for microscopic observation.
Preparation of Mounts and Characterization
of Powdery Mildew
The symptoms of powdery mildew were described based on its appearance on the
actual specimens. The mounts were prepared through thin tissue sectioning and simple
scraping. The structures were morphologically characterized based on its structure on the
temporary and permanent mounts prepared and observed under the microscope.
Characterization was done using the illustrated genera of plant pathogenic fungi in tropics
(Quimio and Hanlin 1999) and the powdery mildews (Spencer, 1987) based on the
following criteria: size and shape of the conidia, color of the conidia, number of conidia
(borne singly or in chain), base of the conidiophore and mode of attachment of the
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
15
conidia from the conidiophores. The conidial measurement was done by the use of an
ocular micrometer. There were 20 conidia measured in each specimen and the average
mean was obtained.
Measurement of Conidia
The conidia were measured exactly with the use of a calibrated microscope. The
ocular micrometer was inserted in the eyepiece of the microscope and the mounts of
conidia were placed on the stage of the microscope. Focusing was done at the lower
power objective (LPO) and shifting to the high power objective (HPO). The ocular
divisions were counted from 0 µm – 100 µm as cited by Esiong (2004).
Data Gathered
1. Shape of the conidia. The observations were done based on the appearance of the
conidia on the focused specimens under the microscope. It was characterized whether
pointed, barrel-shaped or ellipsoidal.
2. Color of the conidia. The observations were done based on the appearance of the
conidia on the focused specimens under the microscope. It was characterized whether it is
hyaline, light to dark brown and others.
3. Size of the conidia. A total of twenty conidia were measured using the ocular
micrometer inserted on the eyepiece of the microscope. The total mean was obtained after
the measurement.
4. Number of conidia. The observations were done based on the appearance of the
conidia on the focused specimens under the microscope. It was characterized whether the
conidia was borne singly or in chains.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
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5. Base of the conidiophore. The observations were done based on the appearance
of the base of the conidiophore on the focused specimens under the microscope. It was
characterized whether it is twisted or not.
6. The manner of attachment of the conidiophores to the host cell. The observations
were done based on where the conidiophore was attached on the focused specimens
under the microscope; whether it is attached on the epidermal host cell or arises from the
stomata.
RESULTS AND DISCUSSION
Characterization of Powdery
Mildew Infecting French Bean
and the Weed Galinsogaparviflora
The powdery mildew infecting French bean (Bokod variety) and the weed
Galinsogaparviflora was characterized as follows (Table 1).
Table 1. Characteristics of powdery mildew infecting French bean and Galinsoga
parviflora
CRITERIA
FRENCH BEAN (BOKOD VARIETY)
AND THE WEED G. parviflora
Size of Conidia
16.45 to 17 µm
Shape of Conidia
Ellipsoidal
Color of Conidia
Hyaline
Number of Conidia Attached to
Conidia borne singly
Conidiophore
Base of the Conidiophore
Not twisted
Attachment of Conidiophore to
On host epidermal cells
the Host
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
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Table 2 below shows the size of the measured conidia of
OidiumpolygoniDC.infecting French bean (Bokod variety) and the weed G. parviflora.
Based from the result, most of the conidia of O. polygoniDC.on the Bokod
varietymeasured 16 µm to 17 µm but some measured 15 to 18 µm (Figure 1b-c).
On the other hand, O. polygoniDC.onG. parviflora has a conidia 13, 14, 15, 18,
19 and 22 µm; although the dominant size is 16 µm (Figure 2c).
The size of the conidia measured in the study is close to the 15 µm size of conidia
as cited by Dugan and Glawe (2007) (Figure 3a-b).
Table 2. Number and size of measured conidia (µm) of powdery mildew infecting French
bean (Bokod variety) and the weed G. parviflora
NUMBER OF CONIDIA
SIZE (µm)
MEASURED
FRENCH BEAN (BOKOD
G. parviflora
VARIETY)
1 16
19
2 17
16
3 18
13
4 17
17
5 17
17
6 16
17
7
17
14
8 18
15
9 16
14
10 18
18
11 16
19
12 16
17
13 16
16
14 16
22
15 16
15
16 16
14
17 16
19
18 16
17
19 16
14
20 15
15
MEAN 16.45
16.4
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
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18
17 µm
16 µm
a
b
c
Figure 1a. Powdery mildew on French bean (Bokod variety)
b-c. Conidia of OidiumpolygoniDC. (16.45-17 µm) at 400x;
b
a
16 µm
17 µm
c
d
Figure 2a-b. Stems and leaves of G. parviflorainfected with
powdery mildew as shown by circle and arrow
c-d. Conidia and size (16,17 µm) of O. polygoniDC.
infectingG. parviflora (400x)
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
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19
a
b
15 µm
Figure 3a. Conidia attached to Conidiophore as
indicated by arrow (Pantaky, 2010)
b. Conidia of O. polygoniDC. (15 µm)
by (Dugan and Glawe,2007)
Shape of the conidia.Based on microscopic observation, the conidia of
Oidiumpolygoni DC.areellipsoidal and hyaline as shown in Figure 4.
Figure 4.Single, ellipsoidal conidia of O.
polygoniDC. attached to
conidiophore as indicated by arrow
(400x)
Base of conidiophore. It was observed that the base of conidiophore of O.
polygoni DC.was not twisted (Figure 5).
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
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Figure 5.Conidia of O. polygoniDC.attached
to the Conidiophore as indicated by
arrow(400x)
Mode of attachment of the conidiophore to the host cell. It was observedthat the
conidiophore of the powdery from French bean (Bokod variety) and G. parviflorawas
anchored to the epidermal cell of the host or it has a superficial mycelia attached to the
host cell. The conidiophore is septated (Figure 6).
a
b
Figure 6 a. Conidiophore bearing the conidia of O. polygoniDC. attached to the host
cell (400x); b. Conidia borne singly and detaches as it matures as shown by
arrow
(400x)
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
21
Characterization of Powdery Mildew
Infecting Ageratum conyzoides
The powdery mildew infecting Ageratum conyzoideswas characterized as follows
(Table 3.)
Table 3. Characteristics of powdery mildew infecting the weed Ageratum conyzoides
CRITERIA
Ageratum conyzoides
Size of Conidia
16.45o 17 µm
Shape of Conidia
Ellipsoidal
Color of Conidia
Hyaline
Number of Conidia Attached to
Conidia borne singly
Conidiophore
Base of the Conidiophore
Not twisted
Attachment of Conidiophore to the Host
On host epidermal cells
This result was corroborated by (Quimio and Hanlin, 1990); (Dugan and Glawe,
2007) and (Spencer, 1987).
Table 4 below shows the size of the measured conidia from the powdery mildew
infected leaves of A. conyzoides. Based the result, most of the conidia
Oidiumcichoracearum DC.measured 11,12 and 13µm. The most dominant size is 11 µm
(Figure 7).
The size of the conidia measured in the study is close to the 12.5-18 µm size of
conidia of O. cichoracearumDC. cited by (Glaweet al., 2006) as shown in Figure 7e.
Table 4.Number and size of measured conidia (µm) of powdery mildew on the weed A.
conyzoides
NUMBER OF THE CONIDIA MEASURED
SIZE (µm)
1
12
2 11
3 11
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
22
4 11
5 11
6 11
7
12
8 13
9 12
10 11
11 12
12 12
13 13
14 12
15 11
16 12
17 11
18 12
19 13
20 11
MEAN 11.7
b
a
Figure 7 a-b. Powdery mildew on A. conyzoides
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
11 µm
23
11 µm
a
b
c 12.5 µm
Figure 7 c-d. Conidia of Oidiumcichoracearum (400x)
e. Conidia attached to conidiophore (Glaweet al., 2006)
Shape of conidia. Based on microscopic observation, the conidia of
OidiumcichoracearumDC. are ellipsoidal and hyaline (Figure 8).
Figure 8. Ellipsoidal conidia in chain as indicated
by arrow(400x)
Base of conidiophore. It was observed that the base of the conidiophore was not
twisted (Figure 9a-b).
Mode of attachment of the conidiophore to the host cell. It was observed that the
conidiophore of the powdery from Ageratum was anchored to the epidermal cell of the
host. The conidiophore is septated (Figure 9a-b).
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
24
Figure 9a-b. Conidia borne in chain attached to the conidiophore that is anchored to
the host cell as indicated by arrow.
Provisionary Key. Below is a simple provisionary key to separate powdery
mildew genera on French bean (Bokod variety), Galinsogaparvifloraand A.
conyzoidesusing the taxonomic referred of Quimio and Hanlin(1999), Dugan and
Glawe(2007) and Spencer 1987
Conidia borne singly
Conidiophore on superficial hyphae
Base of conidiophore not twisted
Conidial size ranges from 16-17 µm,
Conidia ellipsoidal
On herbaceous plants…………………………Oidiumpoygoni DC.
On weeds under Asteraceae family………….OidiumpolygoniDC.
Conidia borne in chain
Conidiophore on superficial hyphae
Base of conidiophore not twisted
Conidial size ranges from 11-12 µm
Conidia
ellipsoidal
on
herbaceous
plants…….(OidiumcichoracearumDC.)
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
25
SUMMARY, CONCLUSION AND RECOMMENDATION
Summary
This study aimed to characterize the powdery mildew on French bean (Bokod
variety) and the weeds (Galinsogaparvifloraand Ageratum conyzoides) and determine if
the same type of powdery mildew infects the Bokod variety grown at BSU Experiment
Station; organic farm and the weeds associated with the crop. Characterization of the
powdery mildew was done by microscopic observation.
Results of the study revealed that the Oidiumpolygoni DC. was the type of
powdery mildew that infects both the French bean (Bokod variety) and the weed
Galinsogaparviflora while Oidiumcichoracearum DC. infects the weed Ageratum
conyzoides.
The characteristics of Oidiumpolygoni DC.were based on the observation using
the taxonomic key of Quimio and Hanlin, 1999; Dugan and Glawe, 2007 and Spencer
1987. The characteristics of OidiumpolygoniDC.includes a conidia that is 16.45-17 µm,
ellipsoidal in shape; hyaline and borne singly; conidiophore on superficial hyphae
attached to the epidermal cell of the host and base of conidiophore not twisted. On the
other hand, the characteristics of the O. cichoracearum DC.are the following: the conidia
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
26
measures 11.7-12 µm, ellipsoidal in shape; hyaline and borne in chain; conidiophore on
superficial hyphae attached on host surface and base of the conidiophore is not twisted.
Conclusion
Based on the results, O.polygoni DC.andO.cichoracearum DC. differ in the size
of conidia and number of conidia attached to the conidiophore (single or in chain). It was
observed that O.polygoni DC. has bigger conidia ranging from 16-17 µm while O.
cichoracearum DC. has a conidia whose size range from 11-12 µm.
Recommendation
In relation to disease management, it is recommended to eradicate the weed
Galinsoga and Ageratum in the field and greenhouse especially when the crops grown are
legumes which include peas, beans and cucurbits. Both harbor the powdery mildew
O.polygoniDC and O. cichoracearumDC.These fungi serve as sources of inoculum for
infection of legumes and cucurbits. In addition, these weeds must be disposed properly.
It is further recommended that studies be conducted on the characterization and
identification other weeds serving as alternative host of powdery mildew diseases.
Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
27
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Characterization of Powdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The
Weeds (Galinsogaparviflora and Ageratum conyzoides) / JovelynGuingabanCamingawan. 2012
Document Outline
- Characterization ofPowdery Mildew Infecting French Beans (Phaseolus vulgaris L.) and The Weeds(Galinsogaparviflora and Ageratum conyzoides)
- BIBLIOGRAPHY
- TABLE OF CONTENTS
- INTRODUCTION
- REVIEW OF LITERATURE
- MATERIALS AND METHODS
- RESULTS AND DISCUSSION
- SUMMARY, CONCLUSION AND RECOMMENDATION
- LITERATURE CITED