BIBLIOGRAPHY BASALONG, JOVYLLE L. ...

BIBLIOGRAPHY

BASALONG, JOVYLLE L. APRIL 2011. Etiology of Stem Rot of Chayote (Sechium
edule). Benguet State University, La Trinidad Benguet.
Adviser: Janet S. Luis, PhD
ABSTRACT

The fungus causing stem rot was isolated from infected chayote stem and was able to
produce similar symptoms on artificially inoculated chayote stems in about four days.

The pathogen is F.oxysporum based on symptom and microscopic properties and is
supported by pathogenicity tests. A pure culture of the fungus produces fast growing and white
to orange color on the media. The fungus has a conidiospore in a sporodochium with an
aggregate and branching formation. Moreover the conidia of the fungus are phialides, slightly
curved, boat-shaped which produces three to five cells and is produced in large number, often in
clumps known as sporodochia.

TABLE OF CONTENTS

Page

Bibliography………………………………………………...................................
i

Abstract………………………………………………………………………….
i
Table of Contents………………………………………………………………...
ii

INTRODUCTION………………………………………………………………
1

REVIEW OF LITERATURE…………………………………………………..
3

MATERIALS AND METHODS……………………………………………….
8
RESULTS AND DISCUSSION……………………………………………….
10

Description of Collection Cite…………………………………………...
10
Disease Symptoms ……………………………………………………….
11

Pathogen Identification…………………………………………………...
12

Growth in PDA...................................................................................
12

Microscopic Characteristics …………………..................................
13

Pathogenicity Test ……………………………………….................. 14

Re-isolation of the Fungal

Isolate from Artificially

Inoculated Stems ……………………….............................................
15

Identity of the Re-isolated Fungus ………………………………......
16

SUMMARY, CONCLUSION AND RECOMMENDATION…………………..
17

Summary…………………………………………………………......
17

Conclusion…………………………………………………………...
17

Recommendation………………………………………………….....
17

LITERATURE CITED…………………………………………………………..
18

1

INTRODUCTION

Chayote (Sechium edule) is a trailing vine-bearing edible fleshy vegetable. It is a
member of the gourd family Cucurbitaceae which may grow to 100 feet (30 m) in length
and each vine may produce up to several hundred fruits (Encyclopedia Americana, 1829).
Chayote is commonly grown in Atok, Kapangan, Kibungan, La Trinidad and
Tublay of Benguet and is a major source of income for farmers. Chayote is also the only
sustainable vegetable in the market because of its availability throughout the year. Hence,
earning the description “green gold” (Fialen, 2004).

Chayote has many uses. The roots, leaves and young shoots are edible for human
and livestock consumption. The fruits can be prepared as pies, pudding, and salads. It is
also a source of food, energy, protein, fats, carbohydrates, vitamins and minerals
(Elstrom, 1990). Chayote fruits and shoots are being sold in the price as low as 50
centavos when there is oversupply and may go as high as 15 to 20 pesos per kilogram
(Velasco, 1994). Chayote has other important uses aside from food purposes. It could be
used as wind breaker in small gullies and slopes destroyed by runoff water. It also
protects the soil from direct rain and helps prevent massive leaching and soil erosion.
In any plant production venture, the occurrence of diseases becomes a limiting
factor. The prevalence of diseases becomes one of the producers’ main problems since
this leads to losses in yield quality and quantity, and eventually loss in income. In order
to boost the production of chayote to supply local market demands, its appropriate
management measures can only be formulated after it has been properly understood.
However, suitable management techniques could only be devised from an understanding
of its etiology.
Etiology of Stem Rot of Chayote (Sechium edule).
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Further tests are then necessary to ascertain the identity of the causal organism
causing stem rot of chayote so that appropriate disease management measures can be
instituted.

This study was conceived and conducted to:

1. Describe the symptoms of the disease;

2. Identify the pathogen causing the stem rot of chayote; and

3. Conduct pathogenicity test using PDA culture as inoculums to a healthy
chayote plant grown from healthy fruit.

The study was conducted from August 2010 to March 2011. Samples were
collected from Mocgo and Puspusok of Sagubo, Kapangan, Benguet and were processed
at the Department of Plant Pathology, BSU, La Trinidad, Benguet.

Etiology of Stem Rot of Chayote (Sechium edule).
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REVIEW OF LITERATURE
Plant Diseases and Their Causes

Plant diseases are deviations from the normal growth and development of plants
incited by microorganisms, parasitic flowering plants, nematodes, viruses, or adverse
environmental conditions (Stevenson, 2002). These are of paramount importance to
humans because these damage plants and plant products on which humans depend for
food, clothing, furniture, the environment, and housing (Agrios, 1997).

The four major consequences of plant diseases are: These may limit the kinds of
plants and industries in an area, these reduce the quality and quantity of plant produce,
these make plants poisonous to humans and animals, and these may cause financial
losses.

Plant diseases are considered one of the many natural hazards in crop production.
These undoubtedly arose and developed on earth. These are named according to the
organisms which cause the diseases. On the other hand, these may also be named
according to the appearance of the plant after supporting a particular disease organism.
The Host

Chayote (Sechium edule) is a perennial tropical vine. It grows in tropical climate
and bears fruit over a period of several months.

Chayote grows best in rich, well drained, sandy loam soils Purseglove (1968) as
cited by Payangdo (2008). It is also adapted to an altitude of 800 - 2,200 meters above
sea level with temperature ranging from 16 - 25oC. It is a warm season crop and a good
bloom is enhanced by short day. Likewise, chayote could be grown in temperate climates
Etiology of Stem Rot of Chayote (Sechium edule).
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by artificially controlling daylength (Aung and Kushad, 1990). After 6 to 8 weeks of
growth, the vine can be shaded with dark cloth on a frame to keep sunlight to 8 hours
each day for the next 4-6 weeks. The frame could be moved to shade the vines at about
4:00 P.M. and removed after sunrise at about 8:00 A.M. the following day. After flowers
develop, the vines can grow under normal daylength. Moreover, observations revealed
that chayote production from sunny side areas yield more fruits per vine than those grown
in leeside areas. This lower yield noted from the leeside areas was considered as the
effect of the lower temperature and less hours of sunlight intensity in the area. Pursegrove
(1986) as cited by Payangdo (2008) claimed that chayote is a warm season crop that if
grown in less favorable condition, it will have luxuriant vine growth but reduced fruit
production.

Chayote plants are sensitive to wind damage during strong typhoons. Therefore,
production should be located in areas that are not frequented by strong winds especially
during typhoon months. The best place for chayote production is in between 800 and
1,800 meters above sea level with a temperature range of 16 - 25oC.

Varieties of chayote that existed in some growing areas in the Philippines since
the nineteenth century are: elongated fruit with deep to slight grooves, non-varieties;
oblong with deep to slight grooves, non-spiny to spiny varieties; Monticello white-oval
shaped and smooth peeled from Puerto Rico and Australian green-oblong with light
groove from Australia.
Fungal Diseases
The chayote’s principal problems in the sub-tropical climate are air-borne and
soil-borne fungi, pathogens like powdery mildew, downy mildew, and anthracnose. Signs
Etiology of Stem Rot of Chayote (Sechium edule).
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of fungal diseases vary but normally the leaves will develop yellow spotches and
eventually the whole leaf will yellow. The infection is most likely in the spring after
planting. The good news is that fungi do not like direct sunlight, extreme heat, and clean
air so infected chayote tend to lose some stems during the summer (preceded by
yellowing of leaves) but win the battle with plant disease in the heat of August and
recuperate for the fall harvest (Rajnauth, 1996).
Fungi and Fungal Diseases

Fungi are organisms that have no true roots, leaves, stems or chlorophyll. Instead,
these have hyphae (microscopic threads) of various types which can grow in the soil or in
a host plant. These threads absorb food from the plant or organic material in the soil.
Fungi cannot make certain necessary food materials so these must live on food products
manufactured by other organisms. Fungi reproduce by various methods. These produce
different types of spores. Some spores are spread by air currents and others by contact or
rain splash. Fungi that cause leaf spots, downy mildew and gummy stem blight produce
hundreds and even thousands of these spores in one spot on a leaf or stem.

Many of the fungi causing seedling blights, root rots, wilts and certain fruit rots
do not produce “heavy duty” spores that are able to survive in the soil for many years.
Fusarium spp. produce chalmydiospores and Pythium spp. produce oospores. This
situation plus the lack of convenient and economical fungicides for use in the soil make it
difficult to control this group of soil-borne fungi. Other fungi produce visible resting
structures called sclerotia. Southern stem rot, caused by Sclerotium rolsfsii, produces
mustard seed-sized sclerotia.
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Fusarium which is suspected to cause stem rot of chayote have been characterized
as causing the following symptoms: vascular wilt, yellows, corm rot, root rot, and
damping-off. The most important of this is vascular wilt. Of the vascular wilt-causing
fusaria, Fusarium oxysporum is the most important species (Agrios, 1988; Smith et al.,
1988). In general, fusarium wilts first appear as slight vein clearing on the outer portion
of the younger leaves, followed by epinasrty (downward drooping) of the older leaves. At
the seedling stage, plants infected by F.oxysporum may wilt and die soon after symptoms
appear. In older plants, vein clearing and leaf epinasty are often followed by stunting,
yellowing of the lower leaves, formation of adventitious roots, wilting of leaves and
young stems, defoliation, marginal necrosis of remaining leaves, and finally death of the
entire plant (Agrios, 1988). Browning of the vascular tissue is strong evidence of
fusarium wilt. Further, on older plants, symptoms generally become more apparent
during the period between blossoming and fruit maturation (Jones et al., 1982; Smith et
al., 1988).
F.oxysporum has no known sexual reproductive stage. Asexual reproductive
structures include both microconidia and macroconidia. Microconidia are abundant, oval
to kidney-shaped, generally one-celled and are formed on short conidiophores.
Microconidia are capable of infecting roots but probably play little role in initial infection
in the field because of their ephemeral nature. Macroconidia are fusiform (“canoe-
shaped”), typically having three to five cells and are produced in large numbers, often in
clumps known as sporodochia. Macroconidia also may infect roots but their primary role
maybe survival as these have the ability to form chlamydospores (sexual resting
structures). Chlamydospores are the primary means of survival and typically form under
Etiology of Stem Rot of Chayote (Sechium edule).
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conditions of sub-optimal growth for the fungus or death of the plant. Fusarium
oxysporum forms two types of chlamydospores: one within the macroconidium and one
form within the mycelium. Those formed from mycelia tend to occur singly or in pairs
and may be either intercalary (within the mycelium) or terminal (occurring at the ends).
Disease results from infection of the root or hypocotyls by hyphae resulting from either
the macroconidia or chlamydospores once infection of the root or hypocotyls by hyphae
results from either the macroconidia or chlamydospores. Once infection has occurred the
fungus penetrates and grows within the xylem. Microconidia are produced within the
vessel, dislodge, and are carried up by the xylem with the transpiration stream,
sporadically germinating and producing more mycelia and microconidia. Wilting occurs
as a result of the formation of tyloses within the xylem by the host. Tyloses are ‘balloon-
like’ invaginations of the xylem parenchyma cells that block the vessel. Tyloses serve to
slow the spread of the pathogen through the plant but also restrict water flow, resulting in
wilting. In addition, the pathogen causes a general breakdown of the xylem parenchyma
cells resulting in various types of gums that add to the blockage. The extent to which
fungal toxins are involved in pathogenesis is not known. Once infection has occurred,
FON is limited to the xylem and generally emerges only after the death of the plant
(Agrios, 1988).

Etiology of Stem Rot of Chayote (Sechium edule).
BASALONG, JOVYLLE L. APRIL 2011

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MATERIALS AND METHODS
Collection of Diseased Materials

Suspected diseased chayote stems were collected from Mocgo and Puspusok of
Sagubo,Kapangan, Benguet. Symptoms of the disease were noted. The samples were
placed individually in transparent plastic bags, labeled and brought for further diagnosis
at the Department of Plant Pathology Laboratory.
Microscopic Examination of Samples

Thin tissue sections were cut from the advancing portion of the lesions and
studied under the microscope. All observations were recorded.
Isolation and Identification of Fungal Isolate

In the laboratory, thin tissue sections were cut from the advancing portion of the
collected samples showing stem rot symptom. These were isolated in potato dextrose
agar (PDA) plates following standard procedures.

To obtain pure culture, the organism was re-isolated in PDA plates. Specimen was
prepared from the pure culture for microscopic examination. It was compared to the
specimen prepared from the natural stem showing the typical symptoms to assure that
both are one and the same.
Pathogenicity Test

Inoculation technique. The suspected Fusarium sp. was isolated and tested for
pathogenicity by inoculation into healthy chayote plants. Two inoculation techniques
were done to compare their effectiveness with an inocolum concentration of 107 spores.
Eight chayote plants were used in the experiment: 4 plants were assigned for each
Etiology of Stem Rot of Chayote (Sechium edule).
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inoculation technique. The inoculated plants were laid in open field and symptoms
developed were observed daily thereafter.
1. Pricking and spraying. Stems were pricked with a sterilized needle before
spraying with fungal suspension prepared from the diseased stems. This method closely
resembles inoculation under natural conditions.
2. Drenching. The soil covering the roots of germinated healthy chayote was sliced
by a sterile knife to assure injury of the roots as avenue for entry of the inocula. The
prepared fungal suspension was drenched to the roots.
Re-isolation of the pathogen. Re-isolation of the pathogen from inoculated test
plants was done using standard procedures. Characteristics of the isolates obtained were
then compared to those of the inoculums used.
Data Gathered

1. Symptoms of the disease. This refers to visual observation of abnormalities
manifested by the infected chayote plant and plant parts. The symptoms seen on the stem
were described, examined and compared to symptom description in available literature.

2. PDA culture identification of isolates. This refers to isolate identification based
on characteristics observed after a week of incubation: colony diameter (mm), growth,
and type and color of mycelia.

3. Microscopic characteristics of isolates. The isolates were characterized as to
microscopic appearance of the hyphae and conidia.
Etiology of Stem Rot of Chayote (Sechium edule).
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4. Pathogenicity test results. These include the effectiveness of the inoculation
method to produce disease and the compliance to the requirement of the disease produced
by artificial inoculation to yield the same isolate as the original inoculum.

Etiology of Stem Rot of Chayote (Sechium edule).
BASALONG, JOVYLLE L. APRIL 2011

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RESULTS AND DISCUSSION
Description of Collection Sites

Chayote stem rots were collected from Puspusok (Figure 1) and Mogco (Figure 2)
of Sagubo, Kapangan, Benguet. An ocular survey of the sites showed widespread
distribution of plants manifesting the symptoms of the disease. Disease incidence is
estimated at about 40%.

Figure 1. Overview of chayote farm at Puspusok, Kapangan, Benguet where symptoms of
Fusarium wilt was assessed at about 40%

Etiology of Stem Rot of Chayote (Sechium edule).
BASALONG, JOVYLLE L. APRIL 2011

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Figure 2. Overview of chayote farm at Mocgo, Kapangan, Benguet where symptoms
of Fusarium wilt was likewise assessed at about 40%

Disease Symptoms

Infection starts with light discoloration at the stem accompanied by wilting of the
plant, which at first may recover during the evening, but plant eventually wilts
permanently. Dull, gray green appearance of upper leaves precedes a loss of turgor
pressure, and wilting and yellowing of the upper leaves. With age, the lesion turns brown
then black (Figure 3). The younger stems are more susceptible than the mature stems.

Fusarium wilts first appear as slight vein - clearing on the outer portion of
younger leaves, followed by (downward drooping) of older leaves. At the seedling stage,
Etiology of Stem Rot of Chayote (Sechium edule).
BASALONG, JOVYLLE L. APRIL 2011

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Figure 3. Symptoms of naturally-infected chayote stem collected
from sampling site

plants infected by F. oxysporum may wilt and die soon after symptoms appear. In older
plants, vein - clearing and leaf epinasty are often followed by stunting, yellowing of
lower leaves, and finally death of the entire plant (Agrios, 1988). Browning of the
vascular tissue is a strong evidence of Fusarium wilt. Further, on older plants, symptoms
generally become more apparent during the period between blossoming and fruit
maturation (Jones et al., 1982 and Smith et al., 1988).
Pathogen Identification

Growth in PDA. The fungus isolated in PDA plate produced fast-growing mycelia
with a diameter of 9mm after a week of incubation at 23-240C, seen as cottony growth
(Figure 4). Generally, the underside was white to orange. These characteristics coincide
with the description of the fusaria including Fusarium oxyporum (Smith et al., 1988). If
sporodochia are abundant, the culture may appear cream or orange in color (Smith,
1988).
Etiology of Stem Rot of Chayote (Sechium edule).
BASALONG, JOVYLLE L. APRIL 2011

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Figure 4. PDA culture of F.oxysporum taken in the seventh day of incubation at
23-240C

Microscopic Characterization

The fungus isolate conforms to F.oxysporum having conidiosphores in a
sporodochium that are branching (Figure 5); conidiogenous cells; phialides with
collarettes; and phialospores either macrospores or macroconidia which are usually
slightly curved or boat-shaped which produce three to five cells (Agrios, 1988).

A
B

C
D

Figure 5. Morphological characteristics of the fungus A) Macroconidia;
B and D) Branching conidiophores in a sporodochium; and C)
Macroconidia in clump formation
Etiology of Stem Rot of Chayote (Sechium edule).
BASALONG, JOVYLLE L. APRIL 2011

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Pathogenicity Test Results
Results of the inoculation methods experiment showed that pricking and spraying
the cell suspension (107) into the cellular spaces with a syringe led to the appearance of
disease symptoms in four days after inoculation (Table 1). However, the symptoms were
manifested only in young stems (Figure 6). While the roots were injured before drenching
the propagule, the non-production of the disease indicates that the pathogen does not
enter the plant through root injury and that drenching the propagules does not ensure
ability to cause infection. The direct pricking of the stem and spraying the propagules
provides immediate contact of the propagules with the plant tissues being attacked by the
pathogen. Pricking and spraying of the fungal suspension proved to be an effective and
efficient way of introducing the pathogen to the host. Test plants that were pricked
showed similar symptoms to the original symptoms observed in the source plant. The
method may have been effective because it permits introduction of a definite number of
fungi uniformly throughout the stem tissue.

Table 1. Pathogenicity of the fungal isolate comparing two inoculation methods with
inoculum level of 107

DAYS
AFTER
INOCULATION

METHOD
4
7
10
13
16
Pricking and spraying a +
++
+++
+++
+++
Drenching b
-
-
-
-
-
Disease rating on the chayote stem: - = no infection, + = stem start to rot, ++ = rotting
on the stem with few visible white mycelia, +++ = stem rot and vascular wilt
a The stems were pricked first before the fungal suspension was sprayed.
b Fungal suspension was drenched to the roots given injury by slicing the soil cover.

Etiology of Stem Rot of Chayote (Sechium edule).
BASALONG, JOVYLLE L. APRIL 2011

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A
B

C
D

Figure 6. Symptoms of the disease on artificially inoculated chayote plants (A,
B, C and D: Pricking and spraying inoculation)
Re-isolation of the Fungal Isolate
from Artificially Inoculated Stems

To complete the proof of pathogenicity as set by Koch’s postulates, fungi from
the artificially inoculated symptomatic plants were re-isolated on PDA. The
characteristics of the fungal isolate that was re-isolated were similar to the characteristics
of the inoculum used (Figure 7). This therefore completes the Koch’s postulates.

Etiology of Stem Rot of Chayote (Sechium edule).
BASALONG, JOVYLLE L. APRIL 2011

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Figure 7. Fusarium oxysporum isolates re- isolated from the artificially
inoculated chayote plant

Identity of the Re-isolated Fungus

On the basis of the cultural and microscopic characteristics of the fungus re-
isolated from the infected chayote stems, the fungus is identified as F. oxysporum. This is
corroborated by the findings of Smith et al. (1988) and Agrios (1988).

Etiology of Stem Rot of Chayote (Sechium edule).
BASALONG, JOVYLLE L. APRIL 2011

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SUMMARY, CONCLUSION AND RECOMMENDATION

Summary
A pure culture of the fungus produced fast - growing cottony mycelia with white
to orange color on the underside of the plate. The fungus has conidiophores in a
sporodochium with an aggregate and branching formation. Moreover, macroconidia of
the fungus are with phialides, slightly curved or boat-shaped which produce three to five
cells and are produced in large number, often in clumps known as sporodochia. In
addition, this fungus can also cause stem rot on artificially inoculated chayote stem in
about four days through the pricking followed by spraying of spores as method of
inoculation.
Conclusion

The pathogen is F.oxysporum as based on symptoms, microscopic observations,
and growth pattern in PDA and as supported by pathogenicity test results.
Recommendation

Although we have gained a better perspective of the stem rot of chayote, we
should, therefore, take advantage of the results obtained and make use of the information
in developing a better management plan of attack.

Etiology of Stem Rot of Chayote (Sechium edule).
BASALONG, JOVYLLE L. APRIL 2011

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LITERATURE CITED
AGRIOS, G. N. 1997. Plant Pathology. 4th ed. New York: Academic Press. P. 803.
AGRIOS, G. N. 1988. Plant Pathology. 3rd ed. San Diego, USA: APS Press. Pp. 407-456.
AUNG, L. H., A. BALL and M. KUSHAD. 1990. Development and Nutritional Aspects

of Chayote (Sechium edule, cucurbitaceae). Econ. Bot. 44:157-164.
ECYCLOPEDIA AMIRICANA. Chayote. 1829. Volume 6. International ed. USA.
332Pp.
FIALEN, J. 2004. Sayote: The Survivor’s Vegeteble. Alipato Publications. 3Pp.
ELSTROM, G.W. 1990. Chayote. The Word Encyclopedia. New York: World Book Inc.
3: 390.

JONES, J. B. and W. MILLER. 1982. Fusarium Wilt. Fla. Dept. Agric. and Consumer
Serv., Div. of Pant Industry. Plant Pathology Circular No.273.

PAYANGDO, G. A. 2008. A Practical Guide in Chayote Production. Benguet State
University, La Trinidad, Benguet. Pp 1-7.

RAJNAUTH, G. L. 1996. Web Blight, A New Disease of Sechium edule. Bulletin OEPP
26: 721-724.

SMITH, I. M., DUNES, J., PHILLIPS, D. H., LELLIOT, R. A. and S. A. ARCHER
(eds.). 1988. European Handbook of Plant Diseases. Blackwell Scientific
Pubications: Oxford. 583Pp.

STEVENSON, J. A. 2002. Plant Diseases. Microsoft ® Encarta ® Reference Library
2003 © 1993-2002 Microsoft Corporation.

VELASCO, R. B. 1994. Benchmark survey on chayote production and marketing
practices in La Trinidad, Benguet. BS Thesis. Benguet State University, La
Trinidad, Benguet. Pp. 2-4.

Etiology of Stem Rot of Chayote (Sechium edule).
BASALONG, JOVYLLE L. APRIL 2011

Document Outline

Etiology of Stem Rot of Chayote (Sechiumedule)
- BIBLIOGRAPHY
- TABLE OF CONTENTS
- INTRODUCTION
- REVIEW OF LITERATURE
- MATERIALS AND METHODS
- RESULTS AND DISCUSSION
- SUMMARY, CONCLUSION AND RECOMMENDATION
- LITERATURE CITED