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Global Insights into Virulence Frequencies of Mycosphaerella graminicola. Z. Eyal, Department of Botany, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, 69978, Israel; A. L. Scharen(2), M. D. Huffman(3), and J. M. Prescott(4). (2)Agricultural Research Service, U. S. Department of Agriculture, Department of Plant Pathology, Montana State University, Bozeman 59717; (3)Department of Mathematical Sciences, Montana State University, Bozeman 59717; (4)The International Maize and Wheat Improvement Center (CIMMYT), El Batan, Mexico. Phytopathology 75:1456-1462. Accepted for publication 8 July 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-1456.

Virulence patterns of 97 isolates of Mycosphaerella graminicola from 22 countries were evaluated on seedlings of 35 wheat and triticale cultivars. Significant isolate x cultivar interactions indicated the existence of specific virulence genes among isolates. Numbers of genes for resistance in cultivars were estimated based on the assumption of a gene-for-gene relationship. Seven hypothetical genes for resistance were estimated in the CIMMYT wheat cultivar Kavkaz-K4500.L.A.4., five in Red Chief, and four each in cultivars Bobwhite S, JCR-979, Volcani 447 (tetraploid), and the triticale cultivar Mapache. Twenty eight hypothesized complementary genes were designated in the 97-isolate x 35-cultivar matrix. These genes were used to determine virulence frequencies of M. graminicola and their geographic distribution. Virulence frequencies varied considerably among the regions (South America, North America, Europe, Mediterranean, Africa, and Oceania) and within countries. South America, including Mexico and Uruguay, had the highest overall virulence frequency. Isolates from South America were more virulent on cultivars originating from South America. Isolates secured from tetraploid wheats in Syria and Tunisia were more virulent on tetraploid cultivars than on hexaploid cultivars. Isolates from the countries of Brazil, Mexico, Uruguay, Israel, Tunisia, Turkey, Ethiopia, and from the state of Oregon in the United States were virulent on a large number of differential cultivars. Differences in geographic distribution of virulences of M. graminicola within regions and countries suggest the feasibility of strategies for germplasm and cultivar deployment for resistance to M. graminicola.

Additional keywords: Septoria tritici blotch of wheat, speckled leaf blotch of wheat.