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Genetics

Contrasting Effects of Asexual Reproduction and Random Mating on Changes in Virulence Frequency in a Field Collection of Uromyces appendiculatus. J. V. Groth, Professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108; E. A. Ozmon, assistant scientist, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Phytopathology 84:566-569. Accepted for publication 17 February 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-566.

A single local field collection of urediniospores of Uromyces appendiculatus was used to initiate a series of sexual (including the entire life cycle of the pathogen) and asexual (urediniospores only) generations on Pinto U.1. 111, a susceptible and presumably nonselective cultivar of bean (Phaseolus vulgaris). In parallel studies of five complete or 10 uredinial generations, virulence frequency was monitored on 15 differential bean lines to which the original collection was polymorphic. These 15 lines were placed in four groups whose members shared the same effective virulence gene. In every case, frequencies of virulence quickly diverged for sexual vs. asexual cycles. For three of the groups, which contained the putative effective genes Ur C, Up 1, and Ur epi, asexual cycling resulted in more change in gene frequency than did sexual cycling. The fourth group, with the line containing Ur N, changed only during the first cycle but changed positively for the asexual and negatively for the sexual cycle.