• 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

• 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 25°C
• RH - 50%

• 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