Production of Sporangia and Oospores ofPhytophthora fragariaein Roots of Strawberry Plants

Four cultivars of strawberry with different levels of resistance to Phytophthora fragariae were inoculated with encysted zoospores of four races of the pathogen. Plants were sampled at 2-day intervals up to 14 days after inoculation, at which time roots were excised and placed in nonsterile soil leachate for an additional 2- to 10-day incubation. Production of sporangia by P. fragariae was greatest when roots of susceptible strawberry cultivar Tennessee Beauty were incubated for a total of 8 days at 15 C after inoculation with isolate NC-1 of race Pf-2. An incubation period of 2−4 days in nonsterile soil leachate was necessary to induce maximum numbers of sporangia (.)