1. Many pathogens can cause postharvest disease in vegetables, tubers, and spices. Important diseases include soft rots caused by bacteria like Erwinia and fungi like Rhizopus and Botrytis. 2. Disease management strategies include physical methods like heat treatment, operational factors like refrigeration and controlled atmospheres, cultural practices, and chemical controls like fungicides. 3. Emerging non-chemical control methods being researched include biological control using antagonistic microorganisms, inducing host resistance through elicitors and treatments, and developing natural fungicides.

1. Academic Program: Bsc.(Hons.)Horticulture
Course : PLPT-516,Diseasesofvegetables, Tubers & spices Crops
Assignment - Important PostHarvest Diseasesof
Vegetables and their Management

3. Vegetables
Cucurbits
Disease pathogen
Anamorph Teleomorph
Bacterialsoftrots Various Erwrtniaspp.,
Bacillus polymyxa,
Pseudomonas syringae,
Xanthomonas campestris
Greymould Botrytiscinerea Botryottniafuckeliana
Fusariumrot Fusariumspp.
Alternariarot Alternariaspp
Charcoalrot Macrophominaphaseolina
Cottonyleak pythiumspp.
Rhizopusrot Rhizopusspp.
Tomato, Eggplant And Capsicum
1. RHIZOPUS ROT- R. STOLANIFER
Symptoms
Water-soaked lesion which exude a clear liquid
Lesion surface may be covered with thin, cotton-like fungal structures (especially under
humid conditions)
Tissues within the lesion are usually held together by relatively coarse strands of fungal
hyphae
Dark sporulation may crown the white tuft of Rhizopus.

4. Bacterial soft rots Various Erwinia spp.,
Bacillus polymyxa,
Pseudomonas spp. and
Xanthomona,s campestris
Grey mould Botrytis cinerea Botryotina fuckeliana
Fusarium rot
Alternaria rot
Cladosporium rot
Fursarium spp. Alternaria
alternata Cladosporium spp.
Rhizopus rot
Watery softrot
Cottony leak
Sclerotium rot Sclerotium rolfsii (sclerotial
Rhrzopus spp.
Sclerotinia spp. Pythium
spp.
Athelia rolfsti
State)
Legumes

5. Grey mould Botrytis cirnerea
B.fabae
Botryotinia fuckeliana
Whitemoulda n d Sclerotiniaspp.
Watery softrot
Cottony leak pythium spp.
Sclerotiumrot Sclerotium rolfsii (sclerotial Athelinrolfstt
state)

6. Brassicas
Bacterialsoftrot Various Erwiniaspp.
Bacillus spp.
Pseudomonas spp. and
Xanthomonas campestris
Greymould Botrytiscinerea Botryotiniafuckeliana
Alternariarot Altenariaspp.
Waterysoftrot Sclerotiniaspp.
Phytophthorarot Phytophthoraporri
Leafy Vegetables
Bacterialsoftrot Various Erwiniaspp.
Pseudomonas spp. and
Xanthomonas campestris
Greymould Botrytiscinerea Botrytiniafuckeliana
Waterysoftrot Sclerotiniaspp.
Onions
Bacterialsoftrot Various Erwiniaspp
Lactobacillus spp. And
Pseudomonas spp.
Blackmouldrot Aspergillus niger
Fusarium basal rot Fusarium oxysporumf.sp.
Cepae
Smudge Colletotrtchumcircinans

7. 1. Blue Mould Rot(Penicillium spp)
Symptoms
Initial symptoms - water soaked areas on the outer surface of scales
Later, a green to blue green, powdery mould may develop on the surface of the lesions
Infected areas of fleshy scales are tan or grey when cut
In advanced stages, infected bulbs may disintegrate into a watery rot.
Blue Mould Rot

8. Carrots
Bacterialsoftrot Various Erwinia spp.and
Pseudomonas spp.
Rhizopusrot Rhizopusspp.
Greymould Botrytiscinerea Botryotiniafuckeliana
Waterysoftrot Sclerotiniaspp.
Sclerotiumrot Sclerotium rolfsii(sclerotialState) Athelinrolfsii
Chalaraand Chalarathielavioides
Thielaviopsis rots Thielautop sis basicola

9. Potatoes
Bacterialsoftrot Erwiniaspp.
Dryrot FLsanumspp. Gibberellaspp.
Gangren Phoma exiguavarexigua
andvar foveata
Blackscurf Rhizoctoniasolani Thanatephoruscucumeris
(sclerotialstate)
Silverscurf Helmtnthosportumsolani
Skinspot Polyscytalumpustulans

10. BHENDI
1. Rhizoctonia rot (Rhizoctoniasolani)
2. Symptoms
Pod - greenish color turning brown, and the infected tissues fully covered with mycelia
Internally, immature seeds and placenta were infected and the diseased tissues were light
brown to black
Externally, mycelia tend to be fluffy and lighter in color, forming a large number of dark
sclerotia on the fruit surface.
Rhizoctonia rot
BRINJAL
1. Fruit rot - Phomopsisvexans
Symptoms
First phase - blight on young seedlings
Stem - girdled slightly above the soil line, plant topples and dies
Stem lesion - dark brown, becoming grey in the centre as pycnidia develops
Leaf - irregular brown spots
Fruits – soft, watery & decays
Finally black, mummified as pycnidia develop abundantly over the surface.
Fruit rot

11. MANAGEMENT
1. Physicalmethods:Heat treatment particularly hot water
treatmentismostly employed to controlpost-harvestdiseases. Heat
treatment may kill incipient infection, leavesnochemical residues but
may unfavorably alter hostphysiological condition.
2. Operationalfactors:
a. Refrigeratedstorage:
Storage at low temperature delays the development of post-
harvestdiseasesby prevention of ripening and directs inhibition of
pathogen.
b. Controlledormodifiedatmosphere:
It inhibits the rate of respiration of the produceand activity of
decaying organisms. Chilling injury which sometimes enhances
rotting can also be checked through CA storage e.g., cabbages.
c. Low pressureorhypobaricstorage:
Leaf vegetables retain their green colour and ripening is retarded.
d. Commonstorage:
Storage at ambient temperature may be quite satisfactory for onions
and potatoes.
3. Cultural control:
It includes water management, crop rotation, nutrient management
etc. Sanitation measures like removal of infested plan material,
cleaning and sterilization of implants are expected to reduce primary
inoculum.
4. Chemicalcontrol:
Maximum research efforts have been directed towards chemical
control. Large numbers of chemicals are used in different forms.
Postharvest dips in chemicals are more effective and hence most popular
because of:
i) Convenience as amethod,
ii) Compatibility with post-harvest practices e.g., hydro-cooling of
vegetables,
iii)Total submergence for maximumpenetration,
iv) Easy control of temperature andpH.
In India, the control efforts have been mainly concentrated towards
checking the spoilage in more important economic crops suchas
tomatoes and potatoes.

12. Traditional strategies for postharvest disease control and
prevention.
Fungicides
Fungicides are used extensively for postharvest disease control in vegetables.
Timing of application and type of fungicide used depend primarily on the target
pathogen and when infection occurs. Forpostharvest pathogens which infect
producebefore harvest, field application of fungicides is often necessary. This
may involve the repeated application of protectant fungicides during the
growing season, and/or strategic application of systemic fungicides.
In the postharvestsituation, fungicides are often applied to controlinfections
already established in the surface tissues of produceor to protect against
infections which may occur during storage and handling. In the caseof
quiescent field infections present at the time of harvest, fungicides must be able
to penetrate to the site of infection to be effective. Systemic fungicides are
generally used for this purpose.
Postharvest fungicides can be applied as dips, sprays, fumigants, treated wraps
and boxliners or in waxes and coatings. Dips and sprays are very commonly
used and depending on the compound, can take the form of aqueous solutions,
suspensions or emulsions. Fungicides commonly applied as dips or sprays
include the benzimidazoles (e.g. benomyl and thiabendazole) and the triazoles
(e.g. prochloraz and imazalil). The benzimidazole group of fungicides are very
useful for the control of many important postharvest pathogens such as
Penicillium and Colletotrichum. Fumigants, such as sulphur dioxide for the
control of grey mould (caused by Botrytis cinerea) of grape and various
postharvest diseases of lychee, are sometimes used for disease control. Other
fumigants used in certain situations include carbondioxide, ozone and
ammonia. Fruit wraps or box liners impregnated with the fungicide biphenyl are
used in some countries for the control of Penicillium in citrus. Fungicides to
control postharvestdiseases of citrus and some other fruit are often applied to
the fruit in wax on the packing line.

13. Maintenance of host resistanceto infection through manipulation of the
postharvestenvironment.
Hygiene practice:
Maintenance of hygiene at all stages during production and postharvest
handling is critical in minimising sources of inoculum for postharvest diseases.
To most effectively reduce inoculum, a good knowledge of the life cycle of the
pathogen is essential. Sources of inoculum for postharvestdiseases depend
largely on the pathogen and when infection occurs. In the case of postharvest
diseases which arise from preharvest infections, practices which make the crop
environment less favourable to pathogens will help reduce the amount of
infection which occurs during the growing season. In many diseases, overhead
irrigation can encourage pathogen spread and infection, trickle or micro-
sprinkler irrigation systems may be more appropriate. As many pathogens are
soil-borne, minimising contactof leaves and fruit with the soil is desirable.
 Water used for washing or cooling producecan become contaminated
with pathogen propagules if not changed on a regular basis and if a
disinfectant such as chlorine is not incorporated. Water temperature can
alsobeanimportantfactorinthetransferofinoculuminsomesituations. Forexample,
tomatoesharvestedduringhotweather mayhaveahigher temperaturethanthewaterusedto
washthem.Inthisscenario,inoculum presentinthewashing watercanbetakeninbythefruit
tissue,causinghigherlevels ofdiseasessuchasbacterialsoftrot.
 Reject producewhich has not been discarded from the packing shedor
storageenvironmentprovidesanidealsubstrateforpostharvestpathogens.
 Packing and grading equipment, particularly brushes and
rollers,whichisnot cleaned and disinfected on a regular basis can also be
a major source ofinoculum.
 Containers used for storing and transporting fruit can harbourpathogen
propagules,particularlyifrecycledanumberoftimeswithoutpropercleaning.

14. PreharvestFactors
A wide range of preharvest factors influence the development of postharvest
disease. These include the weather (rainfall, temperature, etc.), production
locality, choice of cultivar, cultural practices (pesticide application,
fertilisation, irrigation, planting density, pruning, mulching, fruit bagging,
etc.) and planting material. These factors may have a direct influence on the
development of disease by reducing inoculum sources orby discouraging
infection. Alternatively, they may affect the physiology of the producein a
way that impacts on disease development after harvest. For example, the
application of certain nutrients may improve the 'strength' of the vegetable
skin so that it is less susceptible to injury after harvest and therefore less
prone to invasion by wound pathogens.
Prevention of injury
Asmany postharvestpathogens gain entry through wounds or infect
physiologically-damaged tissue, prevention of injury at all stages during
production,harvestandpostharvesthandlingiscritical.Injuriescanbeeither mechanical
(e.g.cuts,bruisesandabrasions),chemical(e.g.burns),biological(e.g.insect,birdandrodentdamage)or
physiological(e.g.chilling injury, heatinjury). Injuriescanbeminimised bycarefulharvestingand
handlingofproduce,appropriatepackagingofproduce,controllinginsectpestsinthefield,storingproduce
attherecommendedtemperatureandapplyingpostharvesttreatmentscorrectly.
Where injuries are present, the process ofwound healing can be
accelerated in some instances through manipulation of the postharvest
environment (e.g. temperature and humidity) or by application of certain
chemical treatments. Wound healing has been shown to be associated with
resistance to certain postharvest diseases suchas bacterial softrot of potatoes
caused by Erwinia sp.

15. Ionising radiation:
Ionising radiation is another physical treatment that can be used after harvest
to reduce disease in some commodities. Like heat, commodities must be able
to tolerate the doses of ionising radiation required to achieve disease control.
Some commodities are surprisingly tolerant. In other commodities, however,
abnormal ripening, tissue softening and off-flavours can result from applying
ionising radiation at doses lethal to the target pathogens. Poorconsumer
acceptability of food irradiation coupled with high treatment costs pose
additional limitations to the widespread use of this technologr at the present
time.
Emerging technologiesforpostharvestdisease control:
Increasing consumer concerns over the presence of pesticide residues in food
have prompted the search for non-chemical disease control measures.
Fungicides used after harvest are of particular concern becausethey are
applied close to the time of consumption. A number of new approaches to
control postharvestdiseases are currently under investigation, including
biological control, constitutive or induced host resistance and natural
fungicides.
Biologicalcontrol
In recent years, there has been considerable interest in theuseofantagonistic
microorganismsforthe control of postharvest diseases. Such organisms can be
isolated from a variety of sources including fermented food products and the
surfaces of leaves, fruit and vegetables. Once isolated, organisms (whether
they be bacteria, yeasts or filamentous fungi) can be screened in various
ways for inhibition of selected pathogens. In most reported cases, pathogen
inhibitionisgreater when the antagonistisapplied prior to infection taking
place.Forthis reason, control of quiescent field infections (e.g.
CoLLetotrtchum spp.)using postharvest applications of antagonistsisoften
more difficult to achieve than controlof infections occurring after harvest
(e.g. Penicillium spp.)

16. Constitutive and induced host resistance:
Plants possessvarious biochemical and structural defence mechanisms
which protect them against infection. Some of these mechanisms are inplace
beforearrivalofthepathogen(i.e.constitutiveresistance),whileothersareonlyactivatedinresponsetoinfection(i.e.induced
resistance).Comparedtointactplants,relativelylittleisknown about host defence responses in
harvested commodities, although thereisgrowing interest in thisarea.
In contrast to preformed antimicrobial compounds, phytoalexins are only
produced in responseto pathogen invasion, although in some cases they can
be elicited by certain chemical and physical treatments. For example, non-
ionising ultraviolet-C radiation is known to induce production of
phytoalexins in various crops. UV treatment of carrot slices induces
production of 6-methoxymellen which is inhibitory to Botrytis cinerea and
Sclerotinia sclerotiorum.
Chitosan, which is a natural compound present in the cell wall of many
fungi, is another elicitor of host defence responses which is currently being
investigated. Chitosan can stimulate a number of processes including
production of chitinase, accumulation of phytoalexins and increase in
lignification. A wide range of other compounds (e.9. salicylic acid, methyl
jasmonate and phosphonates)and treatments (e.g. heat) can induce host
defences in harvested commodities.
Natural fungicides
Many compounds produced naturally by microorganisms and plants have
fungicidal properties. Chitosan, for example, is not only an elicitor of host
defence responses but also has direct fungicidal action against a range of
postharvest pathogens. Antibiotics produced by various species of
Trichoder"rna"have potent antifungal activity against Botrgtis ctnerea,
Sclerotinta sclerottorum, Cortictum roLJsti and other important plant
pathogens. There are many other natural compounds which have been
isolated and shown to possessconsiderable antifungal activity. Although
these compounds may be more desirable than synthetic chemicals from a
consumer viewpoint, their potential toxicity to humans needs to be evaluated
before useable products are developed. On a positive note, the high
specificity of many of these compounds also means that they biodegrade
readily.

17. Conclusions
A wide variety of fungal and bacterial pathogens cause postharvest disease
in fruit and vegetables. Some of these infect producebefore harvest and then
remain quiescent until conditions are more favourable for disease
development after harvest. Other pathogens infect produceduring and after
harvest through surface injuries. In the development of strategies for
postharvest disease control, it is imperative to take a step back and consider
the production and postharvesthandling systems in their entirety. Many
preharvest factors directly and indirectly influence the development of
postharvest disease, even in the caseof infections initiated after harvest.
Traditionally fungicides have played a central role in postharvest disease
control. However, trends towards reduced chemical usage in horticulture are
forcing the development of new strategies. This provides an exciting
challenge for the 2lst century.
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