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Incompatibility Alleles and Fertility of Typhula idahoensis. G. W. Bruehl, Department of Plant Pathology, Washington State University, Pullman, WA 99164; R. Machtmes(2), R. Kiyomoto(3), and A. Christen(4). (2)(3)(4)Department of Plant Pathology, Washington State University, Pullman, WA 99164; (3)Present address: Del Monte Corporation, P. O. Box 36, San Leandro, CA 94577. Phytopathology 68:1307-1310. Accepted for publication 5 April 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1307.

Monokaryons representing the four mating types of 36 dikaryons of Typhula idahoensis, a tetrapolar species, were obtained from dikaryons from north central Washington. Efforts to obtain monokaryons representing all four mating types from dikaryons collected in Idaho and adjacent Utah failed. We conclude that this species is nearly asexual in Idaho and northern Utah. Twelve alleles of the A and 12 of the B locus were identified in Washington. These alleles were found in several combinations, suggesting interbreeding. When the few vigorous monokaryons from Idaho and Utah were paired with Washington testers, several alleles were common to both populations. Dikaryons from Idaho and Utah, even though almost sterile, usually were more virulent on Sprague winter wheat than were Washington isolates. Our data indicate that a functional sexual stage leads to reduced average virulence in a population.