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Ecology and Epidemiology

Inoculum Potential of Phytophthora infestans and the Development of Potato Late Blight Epidemics. Esther Bashi, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel; Y. Ben-Joseph(2), and J. Rotem(3). (2)(3)Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel. Phytopathology 72:1043-1047. Accepted for publication 29 December 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1043.

The inoculum potential of Phytophthora infestans in potato late blight was studied in four spring and three fall epidemics by recording production, dispersal, deposition, and infectivity of sporangia under various conditions. Fall epidemics were more severe than spring epidemics. There were greater amounts of inoculum in the fall, and dew periods were longer. However, no relation was found between the length of the dew period of any given night and the number of sporangia on leaves the following morning. Numbers of sporangia on leaves decreased during the day, but many sporangia formed at night remained attached to leaves until the following evening. Lesions were free of sporangia only after several dewless nights. Most sporangia were caught in mechanical spore traps in the morning to noon hours; few were caught in the evening and night hours. By contrast, infections that developed on trap plants exposed for discrete time periods among diseased field plants indicated that deposition of sporangia also occurred in the evening and night. Sporangia dispersed late in the day were more infectious than those dispersed early. Therefore, the contribution to epidemics of sporangia, relative to their amounts dispersed at different times of the day, was higher for sporangia dispersed late than for those dispersed early in the day. Survival of attached sporangia in the daytime appeared to be of greater importance in spring epidemics, when high temperatures and high light intensity caused greater loss of viability of dispersed inoculum, than under the more favorable fall conditions.

Additional keywords: epidemiology, spore dispersal, sporulation, spore survival.