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Pathogenicity Associations in Puccinia recondita tritici. L. E. Browder, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, Plant Pathology Department, Kansas State University, Manhattan, KS 66506; M. G. Eversmeyer, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, Plant Pathology Department, Kansas State University, Manhattan, KS 66506. Phytopathology 67:766-771. Accepted for publication 13 December 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-766.

Pathogenicity of population samples of Puccinia recondita f. sp. tritici from eight geographic regions of the United States was analyzed by calculating virulence frequencies to single lines and by association of pathogenicity and association of virulence to all possible combinations of two lines within a set of nine wheat lines, each with a different, single, known gene for low reaction to P. recondita. Associations of pathogenicity were studied by calculating Pathogenicity Association Coefficients (PAC) and Virulence Association Coefficients (VAC) for each possible pair of lines. Marked differences were found in both virulence frequencies and in associations of pathogenicity in different geographic regions. Combinations of host genes for low reaction which can be effectively used for control of leaf rust on wheat are characterized by high PAC and low VAC. These coefficients also are useful in detecting gene combinations in wheat cultivars grown during the time the parasite population sample was collected.

Additional keywords: wheat leaf rust, disease resistance, host:parasite relationships.