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Effects of Cultural Conditions on Sporulation, Germination, and Pathogenicity of Entomosporium maculatum. T. van der Zwet, Research plant pathologist, USDA, West Virginia University, Appalachian Fruit Research Station, Kearneysville 25430; H. F. Stroo, former research technician, West Virginia University, Appalachian Fruit Research Station, Kearneysville 25430, Present address of junior author: Department of Agronomy, Cornell University, Ithaca, NY 14853. Phytopathology 75:94-97. Accepted for publication 19 July 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/Phyto-75-94.

Basic physiological studies of the pear leaf blight fungus, Entomosporium maculatum, resulted in development of a sucrose-casein culture medium that allowed significantly more growth and sporulation than media used previously. E. maculatum was found to require an exogenous source of thiamine, and the sucrose-casein medium allowed sufficient spore production for development of a mass screening program for seedlings. When thiamine was added to potato-dextrose agar, fungal growth rate increased fivefold and conidial production 30-fold. Maximum spore production occurred at 100 lux. Higher light intensities inhibited early growth of colonies but did not affect sporulation if spores were allowed to germinate and grow initially in darkness. Germination in culture was stimulated by glucose but was inhibited by ammonium nitrate and by pear leaf extracts. However, leachates from leaves susceptible to infection stimulated conidial germination in vitro while leachates from resistant leaves had no effect. Cultures lost pathogenicity rapidly, becoming almost avirulent after three transfers. Conidia from colonies maintained in culture for 3 mo were less virulent than conidia kept on diseased leaves at 2 C, and the loss in virulence was inversely related to increased germination and growth in culture.

Additional keywords: brown spot, Fabraea maculata, fruit spot, Pyrus.