BIBLIOGRAPHY DALISAN, OMRAH A. APRIL...
BIBLIOGRAPHY
DALISAN, OMRAH A. APRIL 2008. Identification of Postharvest Disease of
Lettuce (Lactuca sativa L.) at La Trinidad, Cold Storage Facility. Benguet State
University, La Trinidad, Benguet.
Adviser: Aurora F. Piñon, Ph.D.
ABSTRACT
Collection and monitoring of two lettuce farmers on postharvest diseases of
variety Romaine was done at the Cold Storage Facility Wangal, La Trinidad, Benguet. It
was found that only soft rot was identified as the postharvest disease; symptoms was
observed as; soft watery soaked lesions that starts at the fleshy portion of the produce
accompanied by a foul odor and was caused by a Pectobacterium carotovorum that is
rod shape and gram negative.
TABLE OF CONTENTS
Page
Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
REVIEW OF LITERATURE
The Crop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Physiological disorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Pathological disorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Postharvest handling and vegetable quality . . . . . . . . . . . . . . . . . . . . . . . . . . 5
MATERIALS AND METHODS
Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Description of symptoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Morphological characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . 7
Data Gathered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
RESULTS AND DISCUSSION
Soft rot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Importance of the Cold Storage Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
ii
Postharvest Practices of the Farmer Cooperators . . . . . . . . . . . . . . . . . . . . . . 12
SUMMARY, CONCLUSION AND RECOMMENDATION . . . . . .. . . .. . . . . . . . 17
LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 19
iii
INTRODUCTION
Background of Study
Lettuce (Lactuca sativa L.) is one of the very oldest vegetables cultivated by man.
It is known as a popular major salad crop (Snowdon, 1992). Lettuce is rich in mineral
nutrients such as calcium, iron, and magnesium, also rich in vitamins like vitamin A,
thianin and niacin (Anonymous, 2001).
Lettuce varieties can be loosely categorized into four groups: the Crisphead,
Butterhead, Leaf and Romaine or Cos. Crisphead lettuce is probably the most familiar of
the four. A tight, firm crisp head, light green leaves, which characterizes it. It is generally
intolerant of hot weather and will readily bolt or send up a flower stalk under that
summer conditions. Its long growing period also makes it one of the most difficult among
the lettuce varieties to grow. The butter head types have a smaller, softer heads of loosely
folded leaves. The outer leaves may be green or brownish with cream or butter colored
inner leaves. Leaf lettuce has an open growth and does not form a head. Color ranges
from light green to red and bronze, this matures quickly and the easiest to grow. Romaine
or Cos lettuce forms an upright cylindrical heads of tightly folded leaves. It may reach up
to 10 inches in height. Of the four types Romaine is said to be the sweetest (Knott and
Deanon, 1967).
All lettuce types should be harvested when they have reached full size but are still
young and tender. Over mature lettuce is bitter and woody. Leaf lettuce is harvested by
removing individual outer leaves, leaving the center leaves to continue to grow. Butter
head and Romaine types can be harvested by removing the leaves, digging up the whole
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
2
plant or cutting the plant about an inch above the soil surface, usually allowing for a
second harvest. While the crisp head is picked when the center is firm (Wolford, 2006).
Some postharvest diseases of lettuce are white rot, which is also known as
“lettuce drop” in the field, pink rib which causes a diffused area at the midrib base,
bacterial soft rot which is characterized by a wet, slimy decay with extensive brownish
discoloration, and russet spotting which appears on the lower midribs of the outer leaves
(Anonymous, 2003a).
Lettuce is known as highly perishable crop producing shallow roots. Due to
improper postharvest practices such as handling and improper storage, lettuce is easily
damaged and is prone to diseases and deterioration thereby affecting its quality and
quantity. It is the aim of most lettuce growers to increase their yield to supply the needs
of consumers and to meet their domestic demands (Ryder, 1999).
Proper postharvest storage is vital in lettuce production. An ideal condition for
storage is at 1°C (34°F). With daily transport of the product to market, the lettuce may
remain in the cooler for less than one day, but should be cooled for at least 12 hours to
remove the heat from the crop. For highest quality, the lettuce should not be stored more
than 7 days in coolers (Wolford, 2006).
Cold Storage Facility was established in the province through the Department of
Agriculture and the Bureau of Postharvest Research and Extension. It is very important to
farmers because prices of vegetables are not always high. Hence, so farmers tend to store
their commodity at the cold storage while waiting for the price to increase.
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
3
The study aimed to monitor the postharvest diseases of lettuce at the cold storage
facility at Wangal, La Trinidad, Benguet to provide assistance to local farmers to improve
their production, generate income and to minimize postharvest losses.
The study was conducted at the Cold Storage Facility Wangal La Trinidad Benguet
from November to December 2007 to February 2008.
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
4
REVIEW OF LITERATURE
The Crop
Lettuce
(Lactuca sativa L.) belongs to Asteraceae (compositae) family. In plant
kingdom it is the largest dicotyledonous family. This is an annual herb with milky latex
in the leaves and stems, which prefers a slightly acidic pH from 6.0 to 6.5-soil condition
(Ryder, 1999).
Lettuce does not need a lot of water but it does need to be continuously
moistened. Growing lettuce in a semi-shaded to shaded location and using straw mulch
around the plants will help retain moisture. A wand is used in watering to concentrate the
application of water at the base of the plant, not on the leaves. Watering the leaves
encourages diseases and may damage some varieties of the more delicate lettuces (Kerns
and Palumbo, 1996).
Several disorders occur on Romaine lettuce. Some very common disorders are the
following:
Physiological Disorders
Tip burn is a disorder caused in the field and is related to climatic conditions,
variety selection and mineral nutrition. Leaves with tip burn are unsightly as it damages
the leaf margin which makes it susceptible to decay (Cantwell and Suslow, 2005).
Ethylene injury is due to exposure to low concentrations of ethylene gas that stimulates
the production of phenolic compounds, which in turn leads to brown pigments. Russet
spots appear as dark brown spots especially on the midribs. The disorder is strictly
cosmetic but makes the lettuce unmarketable. Symptoms of this disorder in Romaine
lettuce heads are yellowish-reddish-brown large, depressed spots or stains. These are
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
5
most noticeable on the midribs, and may darken and enlarge with time. Brown stain is
caused by exposure to carbon dioxide especially at concentration of above 5%. It also
includes the pink rib disorders associated with heads that are over mature. Higher than
recommended storage temperatures can also lead to an increased incidence of pink rib
with the midribs which have a pinkish coloration (Njue, 2007).
Pathological Disorders
The pathological disorders are the bacterial soft rots which are caused by
numerous bacteria species and result in a slimy breakdown of the infected tissue.
Trimming outer leaves, rapid cooling and low temperature storage will reduce
development of bacterial soft-rots. And the fungal pathogens may also lead to a watery
breakdown of lettuce (watery soft-rot caused by Sclerotinia or gray mold rot caused by
Botrytis cineria) but are distinguished from bacterial soft rots by the development of
black and gray spores( Njue, 2007).
Postharvest Handling and Vegetable Quality
Harvesting
vegetables
should begin at the proper stage, size and quality. Crops
destined for storage should be as free as possible from skin breaks, bruises, spots, rots,
decay and other deterioration. Bruises and mechanical damage not only affected
appearance, they also provide an avenue for the entry of pathogens. To prevent damage,
handle gently and field pack if possible. Besides handling, temperature is another factor
important in maintaining harvest quality. Sanitation is of great concern to protect the
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
6
produce against postharvest diseases, but also to protect consumers from associated food-
borne illnesses (Njue, 2007).
The use of hydrocooling can be done. Hydrocooling is the process of spraying or
immersing vegetable in chilled water. However, before subjecting the lettuce to this
process, the lettuce must be cleaned. Lettuce is very sensitive to ethylene gas so lettuce
should not be stored with vegetables and fruits that give off ethylene gas (Kerns and
Palumbo, 1996).
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
7
MATERIALS AND METHODS
Monitoring of the lettuce samples
This was done by observing the Romaine lettuce heads samples at the Cold
Storage facility and rated accordingly. Assessment was done using the parameters such as
disease incidence, disease severity and quality. Observation was done every 24 hours
.
Description of Symptoms
A detailed description of symptoms was used. Sample of the diseased specimen
were brought to the Plant Pathology Laboratory for further diagnosis and proper
documentation.
Morphological Characterization of the Pathogen
Preparation of semi-permanent mounts was done and observed in the microscope
to determine and characterized the pathogen involved. Isolation was also done to
determine if the causal organism that was observed in the semi-permanent mounts are
similar with the pure culture.
Documentation
Lettuce samples were done for both the symptomatology and the morphological
characterization of the causal agents.
A pure culture of the pathogen was done following the entire method of bacterial
diseases which was the streak method on Nutrient Agar (NA).
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
8
Data gathered
1. Percent disease incidence
% Disease incidence= Total number of samples-no. of diseased samples x 100
Total number of samples
2. Percent disease severity (based on host surface infected) using the rating scale
indicated (Ilag, 1987).
Rating Scale:
Scale Description
1 No infection
2 1-5% of the commodity surface infected
3 6-10% of the commodity surface infected
4 11-25% of the commodity surface infected
5 26-50% of the commodity surface infected
6 Over 50% of the commodity surface infected
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
9
RESULTS AND DISCUSSION
Identified Postharvest Disease
Soft rot (Pectobacterium carotovurum)
Symptom. Soft rot lettuce is characterized as a watery decay coming out from the
infected plant part, with foul odor. As cited by Aliado, 2006 bacterial soft rot of lettuce is
characterized by the appearance of water-soaked lesion at the butt-end of the commodity
(Figure 3).
Fig. 3. Infected with soft rot Fig. 4. Healthy Romaine
Morphological Characteristic of P.carotovurum. Microscopic examination of the
infected tissue from advancing lesion showed the presence of bacterial ooze and it was
further examined using the gram staining method. Result of the gram stain revealed that
the bacterium is gram negative and rod shape, similarly with the result of Aliado, 2006
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
10
that the causal bacterium of soft rot of lettuce Iceberg variety is gram negative and rod
shape (Fig.6).
Cultural Characteristic. The pure culture after two days (48 hours) produced a
light yellow colony in Nutrient Agar (NA) (Fig. 5). The result further confirms the study
of Alaido, that P.carotovurum produced a creamy white colony with margins that is
entire and smooth surface. Elevation is convex and its form is circular.
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
11
Importance of the Cold Storage Facility
The cold chain process of handling of harvested vegetables reduces postharvest
losses and extends the freshness and quality of high value crops. It helps farmers meet the
demand of the market for a year round supply of fresh quality of vegetables and fruits.
There are different components of the cold chain facilities for high value crops
which are packing houses, pre-coolers, cold storage rooms, refrigerated trucks,
refrigerated stalls and chillers in the supermarket and restaurants. After harvest, the
lettuces are brought to the packing house, an area for the trimming, cleaning, sorting, and
grading of the farm produce. From the packing house, the harvested vegetables are
brought to the pre-cooler which immediately remove the field heat from newly harvested
crops. Then to the cold storage to maintain the required temperature and humidity and
allows the perishable crops to be stored for a longer period with a temperature of 2°C.
Refrigerated vans and trucks are used to transport the vegetables from the field to the
cold storage (Fig. 1).
Postharvest Practices of the farmer Cooperators
Harvested lettuces are packed in layers with the plastic crates with 17 to 20 heads in a
lying position. In the case of Mrs. Ching she transports the lettuce in plastic crates using
the refrigerated van, while Mr. Santos uses an elf to transport his harvest from the field to
the cold storage facility. The lettuces are stored at the cold storage facility for one to two
days before they are delivered to the market (Fig. 2).
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
12
Figure 1. Romaine lettuce in a refrigerated van
Figure 2. Cold Storage Facility at Wangal La Trinidad Benguet
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
13
Figure 5. Pure Culture of the bacterial isolate on Nutrient Agar (NA) (48 hours)
Figure 6. Stained bacterial isolate (1000x)
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
14
Table 1. Percent (%) disease incidence
SAMPLES TOTAL
NUMBER
NUMBER OF
PERCENT (%)
OF SAMPLES
DISEASED
INFECTION
SAMPLES
Mr. Santos
17
17
100
Mrs.
Ching 17 15 88.24
From the samples observed with the two farmers, Mrs. Ching had the less number
of diseased samples. The high incidence of soft rot maybe due to the presence of the
bacterium in the plant sample prior to storage. In addition, since lettuces are packed in
crates with out liner, infection may have spread from infected to healthy lettuce.
Table 2. Percent (%) disease severity
SOFT ROT SEVERITY OBTAINED FROM TWO FARMERS ONLY AFTER 24
HOURS OF OBSERVATION
No. of samples
Mrs. Ching
Mr. Santos
1 1
2
2 2
3
3 2
3
4 2 2
5 2 3
6 1 3
7 3
2
8 2 2
9 2 3
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
15
Table 2. Continued…
SOFT ROT SEVERITY OBTAINED FROM TWO FARMERS ONLY AFTER 24
HOURS OF OBSERVATION
No. of samples
Mrs. Ching
Mr. Santos
10
2
2
11
2
3
12 3 2
13 2 3
14 2 2
15 2 3
16 2 3
17 2 3
% Disease Severity (based on host surface infected) using the rating scale (Ilag, 1987).
Rating Scale:
Scale Description
1 no infection
2 1-5% of the commodity surface infected
3 6-10% of the commodity surface infected
4 11-25% of the commodity surface infected
5 26-50% of the commodity surface infected
6 over 50% of the commodity surface infected
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
16
The 88% and 100% soft rot infection observed from lettuce obtained from Mr.
Santos and Mrs. Ching can be due to the soft rot P. caratovorum.
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
17
SUMMARY, CONCLUSION AND RECOMMENDATIONS
Summary
Collection of postharvest diseased Romaine lettuce heads was done at Wangal
Cold Storage Facility, La Trinidad, Benguet from two farmers. Diseased Romaine lettuce
heads were place or incubated in clean plastic bags for further diagnosis of postharvest
diseases. Morphological characterization and isolation of the pathogen was done at the
Department of Plant Pathology following the pathoginicity test for plant pathogens
(Koch’s postulate). Bacterial pathogen associated with Romaine lettuce heads was
identified through symptomatology, morphological and cultural characters of the
pathogen.
Conclusion
The postharvest disease of Romaine lettuce at the Cold Storage Facility was
identified as soft rot of vegetable caused by Pectobacterium carotovorum.
Recommendations
1. A follow-up studies must be done to identify other postharvest diseases of
lettuce.
2. Prior to storage, vegetables must be properly cleaned or trimmed-off of
diseased portion should be done.
3. Farmers using the facility should follow postharvest and storage practices like
the trimming (removal of outer leaves), only healthy and uninfected commodity should
be stored. When packing leafy vegetables in plastic crates, liners be placed at the butt end
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
18
of the commodity and should be stored in an upright position to lessen the spread of soft
rot infection.
4. Proper sanitation should be observed like the disinfection of the plastic crates
with 10% chlorox before use.
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
19
LITERATURE CITED
ALIADO, J.S. 2006. Identification of Pre and Postharvest Diseases of Iceberg Lettuce
(Lactuca sativa L) BS Thesis. Benguet State University, La Trinidad Benguet.
Pp17-18.
ANONYMOUS, 2001. Nutritional Value of Lettuce. Posted at Nutrition about. Com/
library/foodfind/ lettuce.htm
ANONYMOUS, 2003. Lettuce, Commercial Vegetable production Guides, North
Willamette Research and Extension Center. Retrieved 06 March from www.orst.
Edu/dept/NWREC /lettuce.html.
BANSE, G. 2005. Growing Lettuce/Farm and Garden. Retrieved 06 March from
www.Farm-garden.com/growing-vegetables/lettuce
CANTWELL, M and T. SUSLOW. 2005. Lettuce: Romaine or cos. Recommendations
for Maintaining postharvest Quality. Produce Facts/veg/romaine, shtml
KERNS, D.L. and J.C. PALUMBO.1996. Lettuce IPM; Southwestern USA. Ipmworld.
Umn. Edu/chapters/kerns.htm
KNOTT, J.F. and R. DEANON. 1967. Vegetable Production in Southeast Asia. Los
Banos, Laguna. University of the Philippines, College of Agriculture. Pp.318-321
ILAG, L.L. 1987. Learning The Principles Of Plant Pathology. University of the
Phillipines Los Banos Laguna. Pp.167
MARIANNE, R. 2000. My first garden Vegetable Dictionary. Ohio State University
Extension
NJUE, O. 2007. Postharvest Handling and Vegetable Quality. Arkkansas University, Pine
Bluff.
RYDER, E.J. 1999. Lettuce, Endive and Chicory, Crop Production Science in
Horticulture
SNOWDON, A. L. 1992. Postharvest Disease and Disorders of Fruits and Vegetables,
CRC Press Inc., Wolfe Pub., LTD., Florida, USA. Pp. 182-97. Vol.I
WOLFORD, R. 2006. Watch your garden Grown Lettuce. Extension Educator Urban
Horticulture and Gardening. Extension Educator- Nutrition and Wellness,
University of Illinois. Retrieved 06 March from htp//www. urbanext.
Neggies/lettuce/html.
Identification of Postharvest Disease of Lettuce (Lactuca sativa L.)
at La Trinidad, Cold Storage Facility / Omrah A. Dalisan. 2008
Document Outline
- Identification of Postharvest Disease of
Lettuce (Lactuca sativa L.) at La Trinidad, Cold Storage Facility
- BIBLIOGRAPHY
- ABSTRACT
- TABLE OF CONTENTS
- INTRODUCTION
- Background of Study
- REVIEW OF LITERATURE
- The Crop
- Physiological Disorders
- Pathological Disorders
- Postharvest Handling and Vegetable Quality
- MATERIALS AND METHODS
- Monitoring of the lettuce samples
- Description of Symptoms
- Morphological Characterization of the Pathogen
- Documentation
- Data gathered
- RESULTS AND DISCUSSION
- Identified Postharvest Disease
- Importance of the Cold Storage Facility
- Postharvest Practices of the farmer Cooperators
- SUMMARY, CONCLUSION AND RECOMMENDATIONS
- Summary
- Conclusion
- Recommendations
- LITERATURE CITED