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Effect of Temperature, Relative Humidity, and Rehydration Rate on Germination of Dried Sporangia of Phytophthora infestans. K. P. Minogue, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; W. E. Fry, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 71:1181-1184. Accepted for publication 4 March 1981. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-1181.

The ability of sporangia of Phytophthora infestans 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. About 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, fewer than 1% germinated. Differences in the rate of rehydration appear to 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 C and was not significantly affected by relative humidity (RH) between 40 and 88% at these temperatures. The average half-life of the sporangial population under these conditions was 5.5 hr. The death rate was significantly faster at 30 C; the half-life at this temperature was 1.4 hr at 40% RH and 3.8 hr at 88% RH.