POST HARVEST DISEASES

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POST HARVEST DISEASES OF CUCURBITS
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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

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Older, and greatly enlarged lesions on a melon
leaf
Lesions on watermelon are irregular and turn dark
brown or black
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• 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

Lesion on watermelon showing a gelatinous mass
of salmon colored spores
Melon showing the blackened center of the lesion
and a hint of the pinkish spore mass
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• 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
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• 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, 100RH

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• Management
• Field sanitation - destroy the plant debris
• Hot water treatment of seeds _at_ 57.2oc for 20 min
• Seed treatment - thiram or carbendazim or
  mancozeb _at_ 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

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Gummy stem blight and black spot Didymella
bryoniae

• Leaf - water-soaked lesion, inter veinal
  necrotic scorch
• Lesions - surrounded by a yellow halo, when
  spots dry up, they often crack

• Stems - water-soaked lesions and later appear tan
• Stem lesions often cause gummy, reddish -brown or
  black beads to exude

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• 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

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• 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
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• 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

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• 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

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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

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

Fertile head
Sporangia and fertile heads
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• 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

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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

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• 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

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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
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• 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 10C (50F) will retard
  disease development during transit and storage

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Diplodia fruit rot of watermelon and
cucumberDiplodia 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

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• 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

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• 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

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• 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

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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

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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.

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• 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

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• 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
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• 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.