• 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

• Do not develop any mycelium
• Produce summer sporangia – thin walled
• Sporangia release zoospores which attack the tubers

Mode of spread and survival :

• 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 17.8°C
• Presence of oxygen and nitrates in soil favours the germination of sporangia

• Resistant cultivars - Kufri Kanchar, Kufri Sherpa, Kufri Jyoti
• Steam sterilization of soil
• Soil treatment – mercuric chloride and formalin 5%