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Races of Puccinia graminis in the United States and Mexico During 1984. A. P. Roelfs, Research Plant Pathologist, Cereal Rust Laboratory, ARS, USDA, University of Minnesota, St. Paul 55108. D. H. Casper, Research Technician, and D. L. Long, Plant Pathologist, Cereal Rust Laboratory, ARS, USDA, University of Minnesota, St. Paul 55108. Plant Dis. 69:955-958. Accepted for publication 27 March 1985. 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, 1985. DOI: 10.1094/PD-69-955.

Oat stem rust was present in trace amounts throughout the United States in 1984. Disease development was generally more than a week later than the 40-yr average. Losses were light throughout the United States. The principal race in the United States and Mexico was NA-27, virulent on hosts with resistance genes Pg-1, -2, -3, -4, and -8. NA-27 made up 94 and 100% of the isolates from the United States and Mexico, respectively. No virulence was found in oat stem rust for hosts with genes Pg-9, -13, -16, or -a. Wheat stem rust was found in trace amounts in trap plots near Uvalde and Victoria in southern Texas in early April. Additional overwintering sites were found in nurseries at Giddings, TX; Quincy, FL; Tifton, GA; and Jeanerette and Crowley, LA; and in a commercial field near Kaplan, LA. Stem rust spread northward into the northern Great Plains by mid-June. Although stem rust occurred on some hard red spring wheat cultivars, they had adequate resistance to prevent the massive inoculum concentrations that developed in 1953 and 1954, and losses were nil. Race 15-TNM, virulent on plants with Sr17, was the most common virulence combination, making up 74% of the 870 isolates from 324 collections. The second most common race was 15-TNM, avirulent on hosts with Sr17, which made up 9% of the isolates. No virulence was found on wheat lines with genes Sr13, 22, 24, 25, 26, 27, 29, 30, 31, 32, 33, 37, Gt, and Wld-1.