Infectivity of asexual propagules of Phytophthora infestans in sterile peat exposed to various temperature regimes

Survival of asexual (sporangia and mycelium) propagules of Phytophthora inf estans in autoclaved peat moss exposed to various temperatures was assessed by ability to infect floating potato leaf discs. Infectivity of propagules in peat was measured after 0, 21, 35, 63, and 79 days of exposure to tempe ratures ranging from -33 degreesC to 20 degreesC. Propagules exposed to tem peratures below freezing were no longer infective after 21 days. Exposure o f propagules to temperatures of 15 or 20 degreesC resulted in a rapid decli ne in infectivity over time; by the final sampling date, none were infectiv e. In contrast, propagules exposed to a temperature of 5 degreesC for 79 da ys remained infective.