Post harvest diseases of potato

List of diseasesList 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

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

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

Survival and spreadBlackleg - 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

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

Dry rotF. solaniF. solani var. var. coeruleumcoeruleum

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

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%

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 60°F with good ventilation and a RH of at least 95% for the first 2 to 3 weeks of storage

Brown rotBrown rotRalstonia solanacearumRalstonia 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

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

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

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

In tubers - purplish brown spots & spread to entire surface

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

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

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)

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

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

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 wartPotato wartSynchytrium endobioticumSynchytrium 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 rot Sclerotium rolfsiiSclerotium 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

FungusSilky white myceliumSeptate and branched hyphaeGlobose, 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 - PCNB@ 15 kg/ha Resistant clones - S. acaule, S. multiinerruptum,

S. infundibuliformae Resistant varieties - Kufri Bahar, Kufri Jyoti, Kufri Muthu,

Kufri Sherpa

Charcoal rotCharcoal rotMacrophomina phaseolinaMacrophomina 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

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 scurfSilver scurfSpondyocladium atrovirensSpondyocladium 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’

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