Post harvest diseases of potato

1. Post harvest diseases of potato

2. 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

3. 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

4. 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

5. Survival and spread Blackleg - Erwiniacarotovora subsp. atroseptica • Carried by contaminated seed tubers • Usually dormant and do not cause disease unless environmental conditions are favorable Aerial stem rot - Erwiniacarotovora 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

6. 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

7. 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

8. 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%

9. 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

10. Brown rotRalstoniasolanacearum • 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

11. 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

12. 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

13. 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

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

15. 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).

16. 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

17. 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)

18. 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

19. 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

20. 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

21. Potato wartSynchytriumendobioticum 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

22. 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.

23. 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%

24. Sclerotium rot Sclerotiumrolfsii • 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

25. 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

26. 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

27. Charcoal rotMacrophominaphaseolina • 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

28. 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 - KufriChandramukhi, KufriAlankar

29. Silver scurfSpondyocladiumatrovirens • 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’

30. 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