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Ecology and Epidemiology

Occurrence of Typhula species and Observations on Numbers of Sclerotia in Soil in Winter Wheat Fields in Washington and Idaho. D. L. Jacobs, Former graduate student, Department of Plant Pathology, Washington State University, Pullman 99164-6430; G. W. Bruehl, professor emeritus, Department of Plant Pathology, Washington State University, Pullman 99164-6430. Phytopathology 76:278-282. Accepted for publication 26 September 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-278.

Typhula incarnata developed over a wider geographic area than T. idahoensis or T. ishikariensis, had a competitive advantage in attacking crown and root tissues of wheat (Triticum aestivum) beneath the soil surface, and was relatively prevalent in areas or seasons unfavorable for development of snow mold, 1980-1983. When conditions favored snow mold, T. idahoensis and T. ishikariensis occurred more frequently on leaves than did T. incarnata. As many as 670 total (germinable plus ungerminable) sclerotia per kilogram of dry field soil were found in one site in Oneida County, ID, but populations greater than 450 total sclerotia per kilogram were unusual. Under conditions favoring snow mold, 60-70 germinable sclerotia per kilogram of soil produced near maximum disease severity. Disease severity was positively correlated with a logarithmic increase in inoculum density. Germination of sclerotia incubated on potato-dextrose agar averaged 57% for sclerotia newly formed on winter wheat and 46% for sclerotia of unknown age screened from soil, suggesting that some form of endogenous dormancy is present.