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📈 Diseases of Potato — Late Blight, Wart, Viruses

Diseases of Potato — Late Blight, Wart, Viruses.

Potato (Solanum tuberosum) is the most important vegetable crop in India and the fourth most important food crop globally. It is affected by numerous diseases caused by fungi, oomycetes, bacteria, and viruses.

Late Blight

Causal Organism: Phytophthora infestans (Mont.) de Bary

Late blight is the most devastating disease of potato and was responsible for the Irish Famine. In India, it causes severe losses in the hills and plains during cooler months.

Symptoms

  • Water-soaked, pale green lesions on leaf tips and margins that rapidly enlarge
  • Lesions turn dark brown to purplish-black with a pale green border
  • White, downy sporangial growth on the lower leaf surface under humid conditions
  • Stems develop elongated, dark brown lesions
  • Tubers show irregular, shallow, reddish-brown to purplish patches on the skin; internally, a rusty-brown, granular rot extends inward from the surface

Management

  • Use certified, disease-free seed tubers
  • Spray Mancozeb (0.25%) preventively and switch to Metalaxyl + Mancozeb (Ridomil MZ, 0.25%) at disease onset
  • Hill up soil around stems to prevent sporangia from reaching tubers
  • Harvest tubers 10-15 days after haulm destruction to allow skin suberisation
  • Grow resistant varieties such as Kufri Jyoti, Kufri Girdhari, and Kufri Khyati

Potato Wart

Causal Organism: Synchytrium endobioticum (Schilb.) Percival — an obligate, soil-borne fungus

Potato wart is a quarantine disease in India, restricted to the Darjeeling hills of West Bengal.

Symptoms

  • Large, irregular, cauliflower-like warty outgrowths on tubers, stolons, and stem bases
  • Warts are initially white to green, turning brown to black as they mature and decay
  • Eyes of tubers are the primary infection sites
  • Above-ground symptoms are rare; disease is detected at harvest

Disease Cycle

Resting sporangia can persist in the soil for over 30 years. They germinate to release zoospores that infect meristematic cells, causing abnormal cell proliferation.

Feature Detail
Pathogen type Obligate intracellular parasite
Persistence 30+ years as resting sporangia
Favourable conditions Cool, moist soils (12-18 degrees C)
Quarantine status Notifiable disease in India

Management

  • Strict quarantine measures — do not move seed tubers from infested areas
  • Grow resistant varieties such as Kufri Jyoti and Kufri Sheetman in endemic areas
  • Long crop rotation (7-10 years) without potato
  • Soil treatment is impractical due to the extreme longevity of resting spores

Potato Viruses

Several viruses affect potato, reducing yields by 20-80% depending on the virus and cultivar.

Potato Virus Y (PVY)

  • Symptoms: Vein necrosis, leaf drop, mosaic, and crinkling depending on the strain
  • Vector: Aphids (Myzus persicae) in a non-persistent manner
  • Most economically important potato virus globally

Potato Leaf Roll Virus (PLRV)

  • Symptoms: Upward rolling of lower leaves, leaves become leathery and pale; tubers develop net necrosis internally
  • Vector: Myzus persicae in a persistent, circulative manner

Potato Virus X (PVX)

  • Symptoms: Mild mosaic or interveinal mosaic; often latent in many cultivars
  • Transmission: Mechanical (through contact, machinery, and sap)

Management of Potato Viruses

  • Use virus-free certified seed potatoes produced through tissue culture and meristem culture
  • Control aphid vectors with Imidacloprid or Thiamethoxam
  • Rogue out virus-infected plants during the growing season
  • Seed potato production in high-altitude areas where aphid populations are low

Summary Cheat Sheet

Disease Group Causal Organism Hallmark Symptom Core Management
Late blight Phytophthora infestans Water-soaked lesions with downy growth Mancozeb to Metalaxyl+Mancozeb progression
Potato wart Synchytrium endobioticum Cauliflower-like warts on tubers Quarantine + resistant varieties
Potato viruses PVY, PLRV, PVX Mosaic, leaf roll, stunting Virus-free seed + aphid control + rogueing

References

2 sources • [1] [2]

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