VIEW ARTICLE

Genetics

The Influence of Four Unnecessary Genes for Virulence on the Fitness of Erysiphe graminis f. sp. tritici. C. R. Bronson, Former graduate research assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824, Current address: Department of Plant Pathology, Seed and Weed Sciences, Iowa State University, Ames 50011; A. H. Ellingboe, former professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824, Current address: Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 76:154-158. Accepted for publication 4 April 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-154.

Two isolates of Erysiphe graminis f. sp. tritici that differed in their host range were examined for possible evidence in support of Vanderplank's stabilizing selection hypothesis. Isolate MO-10 was virulent and isolate MS-1 avirulent on wheat line C1 15889 and lines with the Pm2, Pm3a, and Pm4 resistance genes. Genetic analysis of the isolates showed one locus controlling each difference in host range. A mix of the two isolates was grown on cultivar Chancellor (on which both isolates were virulent) in a controlled environment and the relative proportions of each isolate were monitored over successive conidial generations. The frequency of MO-10 decreased and the frequency of MS-1 increased, indicating that MO-10 was less fit than MS-1 under these conditions (s_x* = 0.24). However, when F₁ progeny of the isolates were compared in 8-way mixtures, reduced fitness was found to have segregated independently of the identified virulence loci. The results indicated that the fitness of the progeny was not significantly affected by the unnecessary virulence alleles. No evidence was found to support the hypothesis of stabilizing selection.