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New Pathogenic Variability in Uromyces appendiculatus in North America. J. R. Stavely, Research Plant Pathologist, Microbiology and Plant Pathology Laboratory, Plant Sciences Institute, USDA-ARS, Beltsville, MD 20705. J. R. Steadman, and R. T. McMillan, Jr. Associate Professor, Department of Plant Pathology, University of Nebraska, Lincoln 68583; and Associate Professor, Florida Tropical Research and Education Center, University of Florida, Homestead 33031. Plant Dis. 73:428-432. Accepted for publication 18 January 1989. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1989. DOI: 10.1094/PD-73-0428.

From 43 field collections of urediniospores of Uromyces appendiculatus obtained from nine states, Puerto Rico, and the Dominican Republic from 1983 to 1987, new virulence combinations were identified in 13 single-uredinium isolates, described here as races 5870. Isolates of 11 previously described races were obtained. Two of the new races have broader virulence on the cultivars used to differentiate races than the previously described North American races. Race 67 is the first to produce moderate-size uredinia on a previously resistant selection of the bean cultivar Compuesto Negro Chimaltenango. Others of these newly described races are the first to contain certain important combinations of virulence on some of the more resistant differential cultivars. The implications of these results are discussed in relation to the development of comprehensive and stable rust resistance in the common bean.

Keyword(s): bean rust, Phaseolus vulgaris.