Effect of Temperature, Relative Humidity, and Rehydration Rate on Germination of Dried Sporangia ofPhytophthora infestans

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Abstract
The ability of sporangia of P. infestans [late blight pathogen of potato] to germinate after exposure to an unsaturated atmosphere was studied in relation to the conditions of exposure (temperature, relative humidity and time) and to the rate of rehydration of the sporangia before germination. Approximately 30% of dried sporangia germinated when rehydrated over a period of 2 min in a dew chamber; however, when rehydrated rapidly by immediate transfer from a dry atmosphere to the germination medium, < 1% germinated. Differences in the rate of rehydration apparently account for some of the disagreement among previous researchers over the resistance of sporangia to drying. The sporangial death rate was similar at 15 and 20.degree. C and was not significantly affected by relative humidity (RH) of 40-88% at these temperatures. The average half-life [t1/2] of the sporangial population under these conditions was 5.5 h. The death rate was significantly faster at 30.degree. C; the t1/2 at this temperature was 1.4 h at 40% RH and 3.8 h at 88% RH.