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Pathogenic Specialization in Uromyces phaseoli in the United States and Rust Resistance in Beans. J. R. Stavely, Research Plant Pathologist, Plant Pathology Laboratory, Beltsville Agricultural Research Center, ARS, USDA, Beltsville, MD 20705. Plant Dis. 68:95-99. Accepted for publication 11 August 1983. 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, 1984. DOI: 10.1094/PD-68-95.

Twenty races were identified from single-uredinial isolates of Uromyces phaseoli by using 19 differential bean cultivars. Although these races did not include all of those occurring on beans in the United States, a few major races were included. At least 18 of these races differ from any previously described races of this fungus. A major objective of this research was to obtain races that were virulent on bean cultivars with broad rust resistance. Among such cultivars, Aurora, NEP-2, Olathe, and Mexico 309 are susceptible, respectively, to 9, 6, 6, and 3 of these 20 races. A high degree of variability and great potential for races that break host resistance exist in U. phaseoli. The most resistant cultivar of more than 400 tested was Compuesto Negro Chimaltenango, which was resistant to all 20 races.