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Sexual Incompatibility and Virulence in Typhula idahoensis. R. K. Kiyomoto, Former Research Assistant, Department of Plant Pathology, Washington State University, Pullman 99163. Present address of senior author: Del Monte Corporation, P.O. Box 36, San Leandro, CA 94577; G. W. Bruehl, Professor, Department of Plant Pathology, Washington State University, Pullman 99163. Phytopathology 66:1001-1006. Accepted for publication 13 February 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1001.

Mating-type frequency determined for 35 to 687 monokaryons from three to 13 sporophores of four Typhula idahoensis field dikaryons revealed tetrapolar incompatibility in all isolates, and each sclerotial isolate yielded only four mating types. Matings of tester monokaryons from the four field dikaryons revealed five A alleles and four B alleles. Tests for virulence of six T. idahoensis field dikaryons on four winter wheats that differ in resistance revealed great differences in virulence on a given wheat. Since pathogen isolates showed no differential virulence to host cultivars, there is no evidence for a gene-for-gene host-pathogen relationship. The genetic basis of virulence was tested by forming 129 dikaryons from 28 monokaryons of field dikaryon 5999-5. Host survival following inoculation with these F1 progeny indicated that the parental dikaryon was heterozygous for several genes which determine virulence. A complete spectrum of virulence was observed in F1 and F2 dikaryons. All monokaryons were avirulent. Only a weak correlation was found between dikaryon growth rate on culture media and virulence on the winter wheat cultivar Nugaines. Because all F1 and F2 dikaryons that were tested contained four chromosomes carrying the same complement of incompatibility genes, it is likely that incompatibility genes are not closely linked to virulence genes.