Virulence and Epidemiology ofPuccinia reconditaf. sp.triticiin the United States in 1985

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Abstract
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 Lr16 (11%) was found after 7 yr of near absence. A combination of virulence, attacking both Lr2a both 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.