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Isolates of Puccinia recondita f. sp. tritici were obtained from wheat leaf collection 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 virulencelavirulence 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
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D. L. Long (1994) studied this question.
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