Virulence of Puccinia recondita f. sp. tritici in the United States in 1987

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Abstract
Isolates of Puccinia recondita f. sp. tritici were obtained from wheat [Triticum aestivum] leaf collections made by cooperators and from field rust surveys conducted by the authors in the Great Plains, Ohio Valley, and Gulf Coast states in 1987. Testing of 947 isolates for virulence to 14 single-gene differentially resistant test lines showed 44 virulence/avirulence phenotypes, categorized into nine Unified Numeration races. An increased frequency of virulence to Lr1, 24, and 26 over recent years was found, and combined virulence to Lr16 and 26 was observed for the first time. No virulence was found to 15 of 24 additional entries in a resistant test series. Regional race distribution patterns again suggested that the central United States was a single epidemiological unit.