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Inheritance of Virulence to Three Bean Cultivars in Three Isolates of the Bean Rust Pathogen. B. J. Christ, Former research assistant, Department of Plant Pathology, University of Minnesota, St. Paul 55108, Present address of the senior author: Department of Botany, University of British Columbia, Vancouver, B.C., Canada V6T 1W5.; J. V. Groth, associate professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Phytopathology 72:767-770. Accepted for publication 9 October 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-767.

Two single-pustule collections of the bean rust pathogen (Uromyces phaseoli var. typica), isolates S1-5 and P10-1, gave differential reactions on two bean cultivars, US#3 and Early Gallatin (EG), while both isolates were virulent on Pinto 111. The third isolate, S1-1, was virulent on all three cultivars. Upon selfing, S1-5 did not segregate for virulence, whereas P10-1 and S1-1 segregated only on EG and US#3, respectively. Crosses were made among the three isolates in all combinations. The F1 progeny of P10-1 S1-5 segregated in a ratio of one virulent to one avirulent on EG and US#3, indicating two independent genes for virulence. Combining the results of selfing and of all the crosses, three genes for virulence to the three cultivars were identified. Further proof of the three virulence genes was obtained by selfing, crossing, and backcrossing selected F1 isolates. The three virulence loci were designated as UpA1, UpA2, and UpV3. For two of the genes avirulence was dominant, but for the third, virulence was dominant.

Additional keywords: albino, fungal genetics, gene-for-gene, Phaseolus vulgaris, quantitative inoculation.