Virulence and Epidemiology of Puccinia recondita f. sp. tritici in the United States in 1985. D. L. Long, Plant Pathologist, Cereal Rust Laboratory, USDA, ARS, Department of Plant Pathology, University of Minnesota, St. Paul 55108. J. F. Schafer, and A. P. Roelfs, Research Plant Pathologists, Cereal Rust Laboratory, USDA, ARS, Department of Plant Pathology, University of Minnesota, St. Paul 55108, and J. J. Roberts, Research Plant Pathologist, USDA, ARS, Georgia Agricultural Experiment Station, Experiment 30212. Plant Dis. 70:1107-1110. Accepted for publication 21 July 1986. 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, 1986. DOI: 10.1094/PD-70-1107.

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 and Gulf Coast in 1985. Testing of 1,148 isolates for virulence to 12 single-gene differentially resistant tester lines showed 40 virulence/avirulence phenotypes, which were categorized into nine defined Unified Numeration races. An increased frequency of virulence to Lr 16 (11%) was found after 7 yr of near absence. A combination of virulence, attacking both Lr2a and 9, was identified for the first time. No virulence was found to nine of 18 additional entries in a resistant tester series. Regional race distribution patterns indicated that the central United States was a single epidemiological unit, whereas the eastern region consisted of three partially distinct epidemiological areas.

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