Effects of hot and cold temperatures on the survival of oospores produced by United States strains ofPhytophthora infestans

Oospores produced from matings between US strains ofPhytophthora infestans were subjected to hot or cold temperatures and then evaluated for viability, based on percent germinationin vitro. Of 35 crosses, 3 produced oospores with sufficient germination for replicated assessments of temperature effects. Germination rates were as high as 26%, but the maximum germination percentage varied among crosses. Two additional crosses, one involving isolates from Mexico also had sufficient germination for assessment of temperature effects. Oospores did not germinate after 2 hr treatments at or above 46C, or after 12 hr treatments at 40C. Temperature treatment at -80C suppressed germination. Temperature had a similar effect on oospore germination from all crosses.