Races of Puccinia graminis in the United States and Mexico During 1987. A. P. Roelfs, Research Plant Pathologist, Cereal Rust Laboratory, USDA-ARS, University of Minnesota, St. Paul 55108. D. H. Casper, D. L. Long, and J. J. Roberts. Research Technician, Plant Pathologist, and Research Plant Pathologist, Cereal Rust Laboratory, USDA-ARS, University of Minnesota, St. Paul 55108. Plant Dis. 73:385-388. Accepted for publication 13 December 1988. 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-73-0385.

Oat stem rust was present in light amounts throughout most of the United States during 1987, and yield losses were nil. Disease generally developed more than a week later than the 40-yr average. The principal race in the United States and Mexico was NA-27, virulent on hosts having resistance genes Pg-1, -2, -3, -4, and -8. NA-27 made up 93 and 100% of the isolates from the United States and Mexico, respectively. No virulence was found for Pg-a or Pg-16 in the 1987 oat stem rust population. In 1987, wheat stem rust overwintered in trace amounts from southern Texas to southern Georgia and up the Mississippi Valley to the Tennessee border. Overwintering sites were found near Beeville and Victoria in southern Texas in early April. Additional overwintering sites were found in the Mississippi Valley from the Gulf Coast into central Arkansas and along the Red River in southern Oklahoma in late April. Stem rust spread northward into Kansas and Nebraska by late May and into the northern Great Plains by mid-June. No stem rust was found in fields of hard red spring or durum wheat cultivars. Race 15-TNM, virulent on plants with Sr17, was the most common virulence combination, making up 99% of the 452 isolates from 172 collections. No virulence was found for wheat lines with “single” genes Sr13, 22, 24, 25, 26, 27, 29, 31, 32, 33, 37, Gt, and Wld-1.