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Hybridization of Typhula ishikariensis and T. idahoensis. A. A. Christen, Former research assistant, Department of Plant Pathology, Washington State University, Pullman, WA 99164, Present address of senior author: Irrigated Agriculture Research and Extension Center, Washington State University, Prosser, WA 99350; G. W. Bruehl, professor, Department of Plant Pathology, Washington State University, Pullman, WA 99164. Phytopathology 69:263-266. Accepted for publication 1 September 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-263.

Monokaryons from eight dikaryons each of Typhula ishikariensis and T. idahoensis were paired in 992 interspecific combinations. The 992 pairings resulted in 147 subculturable dikaryons, 124 of which produced sclerotia. Eighty-eight of the dikaryons produced regular clamp connections, but most of these 88 interspecific dikaryons grew slower than intraspecific dikaryons. Sporophores were produced by 13 of the 88 hybrid dikaryons; four of the 13 were fertile and yielded monokaryons. The spores from the four fertile hybrids germinated poorly and produced few vigorous monokaryons. The preponderance of incompatibility in these matings convinces us that the two species are sufficiently separate to merit retention as distinct species. The less vigorous hybrid dikaryons were avirulent, whereas some of the most vigorous interspecific dikaryons were as virulent as field dikaryons of either species. Most hybrid dikaryons produced few sclerotia on diseased leaves. The F1 interspecific dikaryons were often as virulent on red clover as T. ishikariensis, the more virulent species on that host. Virulence on wheat was not closely linked with virulence on clover. Some hybridsí vigor and virulence make their survival in nature a likelihood.