post harvest diseases of cucurbits

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POST HARVEST DISEASES OF CUCURBITS. Anthracnose Colletotrichum lagenarium. Symptoms Older leaves show small, water-soaked or yellowish areas that enlarge rapidly and turn tan to reddish brown Spots - often circular to angular Later, spots may merge, blighting large sections of the leaf - PowerPoint PPT Presentation

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Page 1: POST HARVEST DISEASES  OF CUCURBITS
Page 2: POST HARVEST DISEASES  OF CUCURBITS

AnthracnoseColletotrichum lagenarium

Symptoms Older leaves show small, water-soaked or yellowish areas that

enlarge rapidly and turn tan to reddish brown

Spots - often circular to angular

Later, spots may merge, blighting large sections of the leaf

Petioles and stems - Tan to black, elongated and form slightly sunken streaks called cankers

Attacks Watermelon, Cantaloupe, Cucumber

Squash and pumpkin are almost immune

Page 3: POST HARVEST DISEASES  OF CUCURBITS

Older, and greatly enlarged lesions on a melon leaf

Lesions on watermelon are irregular and turn dark brown or black

Page 4: POST HARVEST DISEASES  OF CUCURBITS

Immature fruit - turn black, shrivel, and die Round, water-soaked spots develop on the older fruit Spots turn dark green to brown with age and may become

sunken Under wet conditions, pinkish-colored spore masses can be

seen oozing out of the sunken spots

Melon showing the blackened center of the lesion and a hint of the pinkish spore

mass

Lesion on watermelon showing a gelatinous mass of salmon colored

spores

Page 5: POST HARVEST DISEASES  OF CUCURBITS

Fungus Mycelium - septate, hyaline when young and dark when old

Setae - brown, thick walled, 2-3 septate

Conidia - hyaline, oblong and single celled

Whisker like setae and conidia

Page 6: POST HARVEST DISEASES  OF CUCURBITS

Mode of spread and survival Soil and seed borne

Fungus overwinters in old cucurbit vines or in weeds for 5 yrs

Anthracnose can appear anytime during the season, but most damage occurs late in the season after the fruit is set

Spread - running water, workers and the insect Pimelia sp.

Epidemiology Warm, wet conditions - favour rapid development and spread

of the disease

Temp - 25oc, 100%RH

Page 7: POST HARVEST DISEASES  OF CUCURBITS

Management Field sanitation - destroy the plant debris

Hot water treatment of seeds @ 57.2oc for 20 min

Seed treatment - thiram or carbendazim or mancozeb @ 2g/kg

Spraying at weekly intervals of ◦ Carbendazim 0.1 %◦ Mancozeb 0.2%◦ Difolaton 0.2%

Fruit dip - 5 min in wash water containing 120 ppm of chlorine helps to prevent infection of healthy fruits

Resistant varieties in watermelon - Black Stone, Congo, Diamond, Charleston

Page 8: POST HARVEST DISEASES  OF CUCURBITS

Gummy stem blight and black spot Didymella bryoniae

Stems - water-soaked lesions and later appear tan

Stem lesions often cause gummy, reddish -brown or black beads to exude

• Leaf - water-soaked lesion, inter veinal necrotic scorch

• Lesions - surrounded by a yellow halo, & when spots dry up, they often crack

Page 9: POST HARVEST DISEASES  OF CUCURBITS

Black rot Affected area - brownish and water soaked

Advanced stages - rind becomes black and deeply wrinkled

Large irregular areas of the fruit become bronzed with distinct concentric rings

Page 10: POST HARVEST DISEASES  OF CUCURBITS

Fungus Pycnidia are produced, giving rise to conidia, which serve as the

primary inoculum

Young pycnidia appear light brown & as they age become black

Conidia - short and cylindrical, with usually one septum near the middle, or they may be unicellular

Pycnidia with prominent ostiole through which conidia are released

Page 11: POST HARVEST DISEASES  OF CUCURBITS

Mode of spread and survival Seed and soil-borne

Survives as dormant mycelium or as chlamydospores

Under moist conditions, they are readily dispersed by splashing water

Epidemiology RH - 85 %

Optimal temperature Watermelon 23.9oc Muskmelon 39oc

Page 12: POST HARVEST DISEASES  OF CUCURBITS

Management Disease-free seed

2-year crop rotation out of all cucurbits

Field sanitation

Fungicides - chlorothalanil, mancozeb and benomyl

Cucumbers - precooled to 10oc or lower temp

Page 13: POST HARVEST DISEASES  OF CUCURBITS

Choanephora wet rot Choanephora cucurbitarum

Symptoms Attacks the blossoms first and progresses into the developing

fruit causing a wet rot at the blossom end

Fruit rot progresses rapidly and can affect entire fruit within one or two days

Sporulation by the fungus appears as spines with dark heads on the surface of infected tissues

Page 14: POST HARVEST DISEASES  OF CUCURBITS

Fungus Produces both conidia and sporangiophores Conidiophores - unbranched and has a spherical head Sporangiophores - unbranched, recurved at the tip, bearing the

sporangium

Sporangia and fertile heads Fertile head

Page 15: POST HARVEST DISEASES  OF CUCURBITS

Mode of spread and survival Attacks cauliflower, cotton, cucumber, pumpkin, radish and

squash Survive as a saprophyte - as chlamydospores and zygospores Spread - air, beetles and bees Management Crop management practices

◦ Reduce soil moisture (raised beds)◦ Prevent fruit injury ◦ Prevent soil contact with the soil (plastic mulches or trellising)

Post harvest losses may be reduced by ◦ Harvesting fruits at proper stage of maturity◦ Minimizing cucurbit fruit injuries at harvest◦ Pre cooling fruit◦ Maintaining relatively low storage temperature

Page 16: POST HARVEST DISEASES  OF CUCURBITS

Fruit rotPythium aphanidermatum

Symptoms Fruits in intimate contact with soil is affected

Forms a luxuriant wooly mycelial mat on the affected fruits

Skin of the friut shows soft, dark green, water soaked lesions

Interior tissue become watery and soft and decaying matter emits a bad odour

Page 17: POST HARVEST DISEASES  OF CUCURBITS

Fungus Mycelium - intra-cellular, hyaline and coenocytic

Oogonia - smooth and spherical

Antheridia - broadly clavate, terminal or intercallary

Spreads among the fruits during the storage and transit

High moisture and temperature - favours the growth

Management Soil drenching with copperoxychloride - 0.25%

Fruits should be kept away from soil

Page 18: POST HARVEST DISEASES  OF CUCURBITS

Belly rotRhizoctonia solani

Dark brown water-soaked decay on the side of the fruit in contact with the soil

Followed by a yellowish-brown discolouration of the fruit surface

Entire fruit rot within few days

Water-soaked lesions

Page 19: POST HARVEST DISEASES  OF CUCURBITS

Fungus Produces pycnidia and sclerotia Pycnidiospores - hyaline, single celled, ovate to ellipsoid

Mode of spread and survival R. solani overwinters in soils as mycelia on plant debris and as

dark brown sclerotia that remain in soil for long periods

Management Pre-harvest sprays of the fungicides

◦ Azoxystrobin◦ Chlorothalonil ◦ Thiophanate-methyl

Holding the fruit at 10°C (50°F) will retard disease development during transit and storage

Page 20: POST HARVEST DISEASES  OF CUCURBITS

Diplodia fruit rot of watermelon and cucumberDiplodia fruit rot of watermelon and cucumberDiplodia natalensisDiplodia natalensis

Symptoms Stems and leaves - blight and wilting Fruit - decay appears around the stem Rind becomes slightly darkened, water soaked and light brown

later Centre of the spots turn black, cracks and wrinkles

Fungus Pycnidia - black and large When young - colourless, thick walled and one celled When mature - dark brown, rough walled and two celled

Page 21: POST HARVEST DISEASES  OF CUCURBITS

Mode of survival - conidia

Mode of spread - wind, farm implements, insects

Management Scratches and bruises must be avoided

Pre cooling after harvest

Harvest fruits with long stems

Cut ends painted with a fungicide paste - copper sulphate

Page 22: POST HARVEST DISEASES  OF CUCURBITS

Curvularia fruit rot - Curvularia ovoidae Rot is characterised by brown to black irregular lesions

Later covered with dense velvety, black conidial mass of the pathogen

Fungus Mycelium - dark coloured

Conidia – septate, inner cells deep brown and outer cells light brown in colour

Page 23: POST HARVEST DISEASES  OF CUCURBITS

Aspergillus fruit rot - Aspergillus flavus and Aspergillus nidulans Water soaked lesions developed on the fruit surface

Covered by greenish or blackish fungal growth at later stage

Geotrichum fruit rot - Geotrichum candidum Rot appears as water soaked lesion on fruit surface

Fruit skin becomes soft, sometimes shows cracks on the lesion and emit bad colour

Fruit skin - small, black, sunken spots are produced

Page 24: POST HARVEST DISEASES  OF CUCURBITS

Bacterial soft rotErwinia carotovora

Infects the fruit via cracks or wounds in the skin Soft rot rapidly disintegrates the flesh, turning it into a soft

mass of leaky tissue Infected fruits typically have a foul odour

Management Avoid injury to the skin Use properly sanitized (i.e. 150 ppm hypochlorous acid)

wash water

Page 25: POST HARVEST DISEASES  OF CUCURBITS

Bacterial Fruit RotXanthomonas campestris pv.cucurbitae

Fruit - small, slightly sunken, circular spots with a tan center and dark brown border

Epidermis may split, spots enlarge, and become sunken

Bacteria can penetrate into the flesh causing fruit rot and other secondary bacteria may invade

Pathogen – seed borne

Disease is common high and occurs frequently after heavy rainfall.

Page 26: POST HARVEST DISEASES  OF CUCURBITS

Management Seed treatments with hot water (50˚ C for twenty minutes) or

10 % Chlorox

Avoid overhead irrigation and working the fields when they are wet

Rotate out of cucurbits for two years

Repeated applications of copper fungicides as a protectant may be helpful

Page 27: POST HARVEST DISEASES  OF CUCURBITS

Phytophthora Fruit Rot (Phytophthora capsici Fruit rot of processing pumpkin caused by P. capsici: Lesions appear on fruit surface; Fruit rot developed on the side contacting the soil; Fruit rot as a result of falling an infected leaf on fruit Severely infected fruits are collapsed.

First indication of sporulation on the earlier water-soaked lesion

Page 28: POST HARVEST DISEASES  OF CUCURBITS

Management Rotation with non-host crops is recommended.

Other hosts are pepper, tomato, eggplant, cocoa, and macadamia.

Manage soil moisture by selecting well-drained fields, avoiding low-lying areas, subsoiling, preparing dome-shaped raised beds for non-vining crops, and not over irrigating.

Movement in soil on equipment is probably an important means by which Phytophthora has been spread between fields and may account for disease occurrence in fields with no history of susceptible crops.