Potato

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Post harvest diseases of
potato
List of diseases
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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
Black leg - Erwinia spp
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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
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very soft and watery
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have a slightly granular consistency
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tissue is cream to tan-colored
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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
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
Management
 Plant only certified, disease-free seed tubers
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Seed treatment
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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
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Harvest tubers only after the vines are completely dead to
ensure skin maturity
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Precautions to minimize cuts and bruises when harvesting and
handling tubers
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Storage - 55-60 F with 90-95% relative humidity for the first 1-2
weeks to promote wound healing
Dry rot
F. solani var. coeruleum
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Dry dark spots appear on the skin which later becomes
sunken and wrinkled with irregular concentric rings
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Spots shrinks and bursts out
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Internal tissue becomes brown and shrunken with cavities
filled with numerous white tufts of mycelium
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Rotting progress into whole tuber which loses much of water
and become dry hard, shriveled and light in weight
Fungus
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Mycelium – branched, septate
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Hyphae break through the skin and form pustules on the surface
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Pustule – closely interwoven hyphae which give rise to branched
conidiophores bearing conidia
Mode of spread and survival
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Contaminated soil - chief source
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Mycelium, conidia and chlamydospores - present in the soil
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Conidia floating in the air or found on the floor and walls of stores infect
injured tubers
Epidemiology
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Temp -15 to 25oC
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RH - 50%
Management
 Avoid injuries to tubers
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Potatoes should be dried thoroughly and then stored in a cool
place
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To speed the healing process, hold tubers at 50° to 60°F with
good ventilation and a RH of at least 95% for the first 2 to 3
weeks of storage
Brown rot
Ralstonia solanacearum
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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
Casual organism
 Gram –ve, rod shaped bacteria, polar flagellum
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Forms no spores and capsules
Mode of spread and survival
 Infected soil and seed tubers - source of infection
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Decay plant parts release masses of bacteria in the soil - viable
from season to season
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Infection through wounds in roots which spread through
vascular system into the stem
Epidemiology
 Soil temp - 25 to 35oC
 Moisture - 50 %
 Optimum pH - 6.2 to 6.6
Management
 Crop rotation - potato-wheat
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High degree of resistance - clones of Solanum phureja
Late blight
Phytophthora infestans
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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
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Tuber show rusty brown necrosis spreading from surface to
the center
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).
Mode of spread and survival
 Infected tubers and infected soil - source of primary infection
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Survival of fungus in fruiting stage or as dormant mycelium
in the soil
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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
Control
 S. demissum and S. phureja - used for breeding for disease
resistant varieties
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Varieties - Kufri Naveen, Kufri Jeevan, Kufri Alenkar, Kufri
Moti
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Bruising of tubers at harvest should be avoided
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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)
Scab
Streptomyces scabies
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Shallow scab – corky tissue which arises from abnormal
proliferation of the cells of the periderm of the tuber
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Lesions vary in size and shape and darker than the healthy
skin
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Corky lesions 1 to 3mm deep and darker than shallow lesions
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Actinomycete attacks young tubers at a early stage of
development
Actinomycete
 Conidia – produced by formation of septa, which contract to
form narrow isthmuses between the cells
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Conidia- cylindrical and hyaline
Mode of spread and survival
 Affects cabbage, carrot, eggplant, onion, radish
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Contaminated soil and infected tubers - source of infection
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Pathogen may survive passage through digestive tract of
animals and hence it may spread with farm yard manure
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
Potato wart
Synchytrium 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
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.
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%
Sclerotium rot
Sclerotium rolfsii
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Thick white strands of fungus appear at the collar region of
the stem and roots
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White fungal hyphae grow on the tubers which later start
rotting and covered by fruiting bodies
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
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 - [email protected] 15 kg/ha
 Resistant clones - S. acaule, S. multiinerruptum,
S. infundibuliformae
 Resistant varieties - Kufri Bahar, Kufri Jyoti, Kufri Muthu,
Kufri Sherpa
Charcoal rot
Macrophomina phaseolina
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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
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
Silver scurf
Spondyocladium atrovirens
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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’
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
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