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Ecology and Epidemiology

Temperature, Free Moisture, and Inoculum Concentration Effects on the Incidence and Development of White Rot of Apple. Frank C. Kohn, Jr., Former graduate research assistant, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens 30602, Present address of senior author: Mobay Chemical Company, Tifton, GA 31794; F. F. Hendrix, professor, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens 30602. Phytopathology 72:313-316. Accepted for publication 22 June 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-313.

The greatest incidence of infection of cultivar Top Red Delicious apples inoculated with Botryosphaeria dothidea conidia occurred at 30 and 35 C. Optimum rot development occurred at temperatures between 26 and 32 C. The temperatures at which lesion size increased most rapidly were in the range of optimum growth of the pathogen in culture. On unwounded apples, inoculum concentrations as high as 3 × 10⁶ B. dothidea conidia per milliliter failed to produce infection, while concentrations as low as 5 × 10³ conidia per milliliter caused as much infection on wounded apples as the maximum inoculum rate tested. When apples were wounded prior to inoculation, there was no significant difference in the infection rate between apples incubated for 0, 4, 8, 12, and 24 hr under a free moisture regime.