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First Report of Virulence to Wheat Leaf Rust Resistance Gene Lr26 in South Africa. Z. A. Pretorius, Grain Crops Research Institute, Bethlehem 9700, South Africa. . Plant Dis. 72:175. Accepted for publication 14 September 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0175F.

Gene Lr26 in wheat (Triticum aestivum L.) has conferred resistance to over 800 cultures of Puccinia recondita Rob. ex Desm. f. sp. tritici tested in South Africa since annual leaf rust surveys were instituted in 1983. The effectiveness of Lr26 and its linkage to the wheat stem rust (P. graminis Pers. f. sp. tritici Eriks. & E. Henn.) resistance gene Sr31 resulted in extensive exploitation of the Lr26 X Sr31 genotype in breeding programs. In March 1987, during surveys of leaf rust oversummering on volunteer wheat, virulence to Lr26 was detected in a uredinial collection (isolate 3SA 140) from the southern Cape Province. The appearance of Lr26 virulence closely followed the release of the spring wheat cultivar Gamtoos, the first local cultivar with Lr26 resistance, in 1985. Gamtoos has the parentage (Kavkaz X Buho'S') X (Kalyansona X Bluebird) and was originally released by CIMMYT as Veery No.3. In pathogenicity studies, isolate 3SA 140 (avirulent to genes Lr3a, 3bg, 3ka, 9, II, 16, 18, 19,20,21,29, and 30 and virulent to Lrl, 2a, 2b, 2c, 10, 14a, 14b, 15, 17,23,24,25,26, and 28) differed only at the Lr26 locus from the predominant race of P. r. f. sp. tritici (isolate 3SA127) in South Africa. The loss of Lr26 resistance is significant in view of the restricted number of effective Lr genes remaining for utilization in South Africa.