Post harvest diseases of potato

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• Post harvest diseases of potato

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List of diseases

• Black Leg - Erwinia carotovora
• Dry rot - Fusarium coeruleum
• Brown rot - Ralstonia solanacearum
• Potato wart - Synchytrium endobioticum
• Late blight - Phytophthora infestans
• Scab - Streptomyces Scabies
• Sclerotium rot - Sclerotium rolfsii
• Silver scurf - Spondyocladium atrovirens
• Charcoal rot - Macrophomina phaseolina

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Black leg - Erwinia spp

• Aerial stem rot tuber soft rot
• Black leg begins from a contaminated seed piece
• Stem bases - an inky-black to light-brown decay,
  extend up the stem from less than an inch to more
  than two feet
• These enlarge into a soft, mushy rot that causes
  entire stems to wilt and die
• Leaves - roll upward at the margins, become
  yellow, wilt often die

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• Potato tubers with soft rot have tissues
• very soft and watery
• have a slightly granular consistency
• tissue is cream to tan-colored
• black border separating diseased from healthy
  areas
• In the early stages, soft-rot decay - odorless
• Later a foul odor and a stringy or slimy decay
  usually develops as secondary decay bacteria
  invade infected tissues

Symptoms of black leg
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• Survival and spread
• Blackleg - Erwinia carotovora subsp. atroseptica
• Carried by contaminated seed tubers
• Usually dormant and do not cause disease unless
  environmental conditions are favorable
• Aerial stem rot - Erwinia carotovora subsp.
  Carotovora
• Contained in infested soil or introduced to the
  crop by irrigation water, wind-blown rain, and
  insects
• Tuber soft rot - caused by either of these
  soft-rot bacteria
• Maggot flies (Hylemyia spp. and Phorlin spp.) -
  spread the black leg and soft rot
• Epidemiology
• High soil temperatures and bruising of seed
  tubers favor seed-piece decay
• RH - 94 to 100 temp - 21 to 29oC

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• Management
• Plant only certified, disease-free seed tubers
• Seed treatment
• Agallol-3(0.25) for 5 min
• Streptomycin sulphate 0.1 for 10 min
• Streptocycline ( 100 ppm) and copper sulphate (
  40 ppm) for 30 min
• Harvest tubers only after the vines are
  completely dead to ensure skin maturity
• Precautions to minimize cuts and bruises when
  harvesting and handling tubers
• Storage - 55-60 F with 90-95 relative humidity
  for the first 1-2 weeks to promote wound healing

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Dry rotF. solani var. coeruleum

• Dry dark spots appear on the skin which later
  becomes sunken and wrinkled with irregular
  concentric rings
• Spots shrinks and bursts out
• Internal tissue becomes brown and shrunken with
  cavities filled with numerous white tufts of
  mycelium
• Rotting progress into whole tuber which loses
  much of water and become dry hard, shriveled and
  light in weight

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• Fungus
• Mycelium branched, septate
• Hyphae break through the skin and form pustules
  on the surface
• Pustule closely interwoven hyphae which give
  rise to branched conidiophores bearing conidia
• Mode of spread and survival
• Contaminated soil - chief source
• Mycelium, conidia and chlamydospores - present in
  the soil
• Conidia floating in the air or found on the floor
  and walls of stores infect injured tubers
• Epidemiology
• Temp -15 to 25oC
• RH - 50

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• Management
• Avoid injuries to tubers
• Potatoes should be dried thoroughly and then
  stored in a cool place
• To speed the healing process, hold tubers at 50
  to 60F with good ventilation and a RH of at
  least 95 for the first 2 to 3 weeks of storage

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Brown rotRalstonia solanacearum

• Bangle blight or bangili
• Leaf- turns bronze colour, shrivel and die
• Vascular system of stem, root, stolon and tuber
  turns brown
• Ring disease - brown ring in the tuber due to
  discolouration of vascular bundles
• Whitish bacterial exudate oozes from the vascular
  system of cut stems and cut tubers

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• Casual organism
• Gram ve, rod shaped bacteria, polar flagellum
• Forms no spores and capsules
• Mode of spread and survival
• Infected soil and seed tubers - source of
  infection
• Decay plant parts release masses of bacteria in
  the soil - viable from season to season
• Infection through wounds in roots which spread
  through vascular system into the stem

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• Epidemiology
• Soil temp - 25 to 35oC
• Moisture - 50
• Optimum pH - 6.2 to 6.6
• Management
• Crop rotation - potato-wheat
• High degree of resistance - clones of Solanum
  phureja

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Late blightPhytophthora infestans

• Irish famine - 1845-46
• Symptoms
• Leaves, stems and tubers
• Water soaked spots appear on leaves, turn purple
  brown finally black colour
• White growth develops on under surface
• Stem breaks at these points and the plant topples

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• In tubers - purplish brown spots spread to
  entire surface
• Tuber show rusty brown necrosis spreading from
  surface to the center

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• Fungus
• Mycelium - endophytic, coenocytic and hyaline
• Sporangiophores arise from internal mycelium
  through stomata on the tubers
• Sporangia - multinucleate, thin walled, hyaline,
  oval shaped
• Zoospores - biflagellate

Phytophthora infestans A, zoospores produced
within the lemon-shaped sporangia (B).
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• Mode of spread and survival
• Infected tubers and infected soil - source of
  primary infection
• Survival of fungus in fruiting stage or as
  dormant mycelium in the soil
• Persisting of perennial mycelium in affected
  tubers from the field, stored and used as seed in
  next season
• Epidemiology
• Cool (12 to 15oC) and humid ( above 90 ) weather
  with rains alternating with warm (20o C) moist
  period

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• Control
• S. demissum and S. phureja - used for breeding
  for disease resistant varieties
• Varieties - Kufri Naveen, Kufri Jeevan, Kufri
  Alenkar, Kufri Moti
• Bruising of tubers at harvest should be avoided
• Regular spraying during growing season gives
  effective control- 10 to 15 days interval
• Brestan 600g/ha
• Zineb 0.2
• Bordeaux mixture 1.0
• Mancozeb (2 kg/ha)

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Scab Streptomyces scabies

• Shallow scab corky tissue which arises from
  abnormal proliferation of the cells of the
  periderm of the tuber
• Lesions vary in size and shape and darker than
  the healthy skin
• Corky lesions 1 to 3mm deep and darker than
  shallow lesions
• Actinomycete attacks young tubers at a early
  stage of development

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• Actinomycete
• Conidia produced by formation of septa, which
  contract to form narrow isthmuses between the
  cells
• Conidia- cylindrical and hyaline
• Mode of spread and survival
• Affects cabbage, carrot, eggplant, onion, radish
• Contaminated soil and infected tubers - source of
  infection
• Pathogen may survive passage through digestive
  tract of animals and hence it may spread with
  farm yard manure

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• Control measures
• Use disease free planting materials
• Soil application of PCNB (30kg/ha) at the time of
  planting
• Green manuring before planting effectively
  reduce disease incidence
• Seed treatment - mercuric chloride 0.1
• High degree of resistance - S. caldasii var.
  glabrescens,
• S. chacoense S. commersonii
• Varieties - Menominee, Russet Rural, Sebago

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Potato wartSynchytrium endobioticum

• Warts
• As small white granular swellings on the eyes
• Remain minute or may become as large as the tuber
• Soft, pulpy, white to begin become black later

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• Fungus
• Do not develop any mycelium
• Produce summer sporangia thin walled
• Sporangia release zoospores which attack the
  tubers

Live resting (winter) sporangium of S.
endobioticum.
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• Mode of survival and spread
• Resting spores - viable in soil for 20-25 yrs
• Withstand passage through the intestines of
  cattle
• Spread - contaminated manure, soil, infected seed
  tubers
• Epidemiology
• Temp - 16.7 to 17.8oc
• Presence of oxygen and nitrates in soil favours
  the germination of sporangia
• Management
• Resistant cultivars - Kufri Kanchar, Kufri
  Sherpa, Kufri Jyoti
• Steam sterilization of soil
• Soil treatment mercuric chloride and formalin
  5

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Sclerotium rot Sclerotium rolfsii

• Thick white strands of fungus appear at the
  collar region of the stem and roots
• White fungal hyphae grow on the tubers which
  later start rotting and covered by fruiting
  bodies

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• Fungus
• Silky white mycelium
• Septate and branched hyphae
• Globose, smooth surfaced sclerotia
• Mode of survival - mycelium and sclerotia
  subsists in soil
• Mode of spread - infected soil, in running water
  on farm implements

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• Epidemiology
• Temp - 30-35oc
• Thrives in sandy or loamy soil which are acidic
• Alternate wet dry soil conditions favour the
  disease development
• Management
• Application of ammonium nitrate to the soil
• Seed tuber treatment - PCNB_at_ 15 kg/ha
• Resistant clones - S. acaule, S. multiinerruptum,
  
• S. infundibuliformae
• Resistant varieties - Kufri Bahar, Kufri Jyoti,
  Kufri Muthu, Kufri Sherpa

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Charcoal rotMacrophomina phaseolina

• Black spot (2-3mm in dia) develops around the
  lenticels which appears as whitish specks at the
  centre
• On cutting - internal tissues shows black patches
  beneath the spots on the surface of the tuber
• Fungus
• Mycelium - sparse or fluffy
• Hyphae - branched, septate and greyish white or
  brown
• Sclerotia - minute, black and smooth
• Conidiophores - simple and rod shaped
• Conidia - one celled, hyaline, oval or elliptical

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• Mode of spread and survival
• Pathogen present in the soil - primary source of
  inoculum
• Entry of fungus - bruising of skin, insect damage
• Sclerotia survive in the soil for more than 3
  yrs
• Epidemiology
• Disease is more severe in wet soil
• Temp - 31oc
• Management
• Avoid bruising of tubers during harvest,
  collection and storage
• Temp of store house should be low
• Early maturing varieties - Kufri Chandramukhi,
  Kufri Alankar

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Silver scurfSpondyocladium atrovirens

• Lesions - brown, slightly depressed and circular
  with fimbriate margins
• Dotted with minute black specks or sclerotia of
  the pathogen
• Organism invades only the cork cells which are
  destroyed and slough off forming a scurf

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• Fungus
• Hyphae septate, branched, hyaline and become
  brown with age
• Conidia- dark brown, club shaped, thick walled
• Hyphae form minute sclerotia
• Pathogen live from season to season on the
  affected tubers and in the soil
• Spread from diseased to healthy tubers in storage
• Management
• Use of disease free seed material
• Seed treatment- mercuric chloride - 0.1 for 30
  min