This results in poor stand establishment and stand density. Ph ytophthora damage is usually found in lower portions of fields where drainage is poor, or in fields with heavy, poorly draining soils. Stem rot lesions may progress up the stem several nodes . Exte nsive root damage and stem rot lead to stunting, poor nodulation, wilting , and mortality . To view a cartoon of the P. sojae disease cycle click here.
Oospores are long-lived and overwinter in soil and crop debris.
They germinate in spring to form zoosporangia. Infection is initiated when complete saturation or flooding of the soil occ urs. Such conditions are neccessary for zoospore release, dispersal and infection. Zoospores follow chemical signals from root exudates, swim to roots and encyst, then infect root cells. Secondary inoculum from zoosporangia can be produced on colonized roots.