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Occurrence and Pathogenicity of Puccinia recondita f. sp. tritici on Wheat in South Africa from 1983 Through 1985. Z. A. Pretorius, Senior Agricultural Researcher, Grain Crops Research Institute, Bethlehem 9700, South Africa. F. H. J. Rijkenberg, and Roy D. Wilcoxson. Professor, Department of Microbiology and Plant Pathology, University of Natal, Pietermaritzburg 3200, South Africa; and Professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Plant Dis. 71:1133-1137. Accepted for publication 2 June 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-1133.

Leaf rust (Puccinia recondita f. sp. tritici) of wheat (Triticum aestivum) was widespread in South Africa during 1983, 1984, and 1985 and often reached epidemic levels. Leaf rust severities were generally high on spring wheat in the Cape Province but varied on spring and winter wheat in the Orange Free State, Transvaal, and Natal. The leaf rust resistance genes Lr1, Lr2a, Lr2b, Lr3a, Lr3bg, Lr3ka, Lr10, Lr11, Lr14a, Lr15, Lr16, Lr17, Lr20, Lr24, and Lr30 acted differentially to the isolates tested. Nine races were identified during the 3-yr period, two of which were collected only from T. durum. A race characterized by the avirulence/virulence formula Lr3a,3bg,3ka, 11,16,20,24,30/1,2a,15,17 was isolated most frequently (35%) in 1983. A similar race, but possessing additional virulence to Lr24, predominated on bread wheat in 1984 (54%) and 1985 (69%). No isolates virulent to resistance genes Lr9, Lr19, Lr21, and Lr26 were found.