Publication no. P-1999-1026-01R

Epidemiology

Survival of Phytophthora infestans Sporangia Exposed to Solar Radiation. Eduardo S. G. Mizubuti, Donald E. Aylor, and William E. Fry. First and third authors: Department of Plant Pathology, Cornell University, Ithaca, NY 14853; second author: Department of Plant Pathology and Ecology, The Connecticut Agricultural Experiment Station, P. O. Box 1106, New Haven 06504. Phytopathology 90:78-84. Accepted for publication 16 September 1999. Copyright 2000 The American Phytopathological Society.

The effect of solar irradiance (SI) on the viability of sporangia of isolates belonging to two clonal lineages, US-1 and US-8, of Phytophthora infestans was assessed. Exposure during a 3-h period on sunny days (SI > 600 W/m(^2)) drastically reduced germination regardless of the time of day of the exposure. After 1 h of exposure on sunny days, the viability of sporangia decreased by approximately 95%, and the effective time necessary to inactivate 95% of the sporangia was 1.1 h. The effective dose to inactivate 95% of the sporangia on sunny days was 2.6 MJ/m(^2). On overcast (SI < 300 W/m(^2)) days, survival after 3 h was reduced only slightly. Thus, other variables being equal, sporangia will survive hours longer in the atmosphere on cloudy days than on sunny days.