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Genetic Analysis of Resistance to Stem Rust in Ten Durum Wheats. R. P. Singh, CIMMYAT (International Maize and Wheat Improvement Center), Lisboa 27, Apdo Postal 6-641, 06600 Mexico, DF; E. Bechere, and O. Abdalla. CIMMYAT (International Maize and Wheat Improvement Center), Lisboa 27, Apdo Postal 6-641, 06600 Mexico, DF. Phytopathology 82:919-922. Accepted for publication 2 April 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-919.

Durum wheat (Triticum turgidum L.) cultivars derived from CIMMYT (International Maize and Wheat Improvement Center) germplasm are currently grown on more than 8 million ha worldwide. Because negligible information is available on their genes for resistance to stem rust, crosses in a diallel arrangement (without reciprocals) were made among nine resistant CIMMYT-derived durums, and Kingfisher, which was susceptible to one Mexican pathotype of Puccinia graminis f. sp. tritici. Parents, F1 plants, F2 populations, and F3 lines were evaluated as seedlings in the greenhouse with two pathotypes and in the field with one pathotype. Cultivar Yavaros 79 possibly carried Sr9e and Sr12, which were also present in Mexicali 75, Diver, Somorguho, and Morus together with an unidentified gene, SrC, and in Altar 84, Carcomun, Totanus, and Woodrail together with SrD. Kingfisher and eight other durums (except Woodrail) also possessed gene SrE, which conferred resistance to pathotype RTR, but not to GFC. Genes Sr9e and SrD conferred immune and high levels of adult plant resistance, respectively; Sr12 conferred only moderate levels of resistance, and SrC was ineffective under field conditions despite its effectiveness at the seedling stage to the same pathotypes. Because resistance was based on few genes, immediate measures are being undertaken to increase genetic diversity in CIMMYT germplasm.