Perpetuation and Survival of Pathogen

Oospores formed in malformed and senesced host tissues constitute an important means of survival of H. parasitica over periods under unfavourable environmental conditions. It is also known to survive through mycelium and conidia for a short period of time. Pathogen is also known to be active during oversummering and overwintering under unfavourable environmental conditions in the diseased debris. Germinating oospores, intact oospores, mycelia, and conidia of H. parasitica were observed in the severely infected macerated host tissues. The maximum conidial discharge of H. parasitica from kohlrabi leaves is between 5 and 6 a.m. (258 conidia/cm2). The conidial discharge decreases greatly from 12 noon to 8 p.m. Maximum conidial germination of H. parasitica from B. juncea was at 20 0C temperature. The germination of oospores of H. parasitica is dependent on temperature, light, pH of the medium, and age of oospores.