Virulence and Diversity of Puccinia recondita f. sp. tritici in the United States in 1991. D. L. Long, Plant Pathologist, USDA-ARS, Cereal Rust Laboratory, Department of Plant Pathology, University of Minnesota, St. Paul 55108. A. P. Roelfs, K. J. Leonard, and J. J. Roberts. Research Plant Pathologist, Research Plant Pathologist, USDA-ARS, Cereal Rust Laboratory, Department of Plant Pathology, University of Minnesota, St. Paul 55108; and Research Plant Pathologist, USDA-ARS, Georgia Agricultural Experiment Station, Experiment 30212. Plant Dis. 77:786-791. Accepted for publication 5 April 1993. 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, 1993. DOI: 10.1094/PD-77-0786.

Isolates of Puccinia recondita f. sp. tritici were obtained from wheat leaf collections made by cooperators throughout the United States and from cereal rust field surveys of the Great Plains, Ohio Valley, and Gulf Coast states in 1991. Fifty-five virulence/avirulence phenotypes were found among 647 single uredinial isolates on 14 host lines that are isogenic for leaf rust resistance. The frequencies of virulence to lines with Lr24 and Lr26 during 1991 were greater than in previous years. Regional race distribution patterns again suggested that the central United States is a single epidemiological unit distinct from the eastern United States. The distinctive racial composition of collections from the Southeast, Northeast, and Ohio Valley indicate that populations of P. r. tritici in those areas are discrete, suggesting epidemics originate from localized overwintering sources.

Keyword(s): plant disease monitoring, rust epidemiology, wheat leaf rust.