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Number of Genes Controlling High-Temperature, Adult-Plant Resistance to Stripe Rust in Wheat. E. A. Milus, Former graduate student, now with Rohm and Haas Seeds, P. O. Box 111, Berthoud, CO 80513; R. F. Line, plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, Washington State University, Pullman 99164-6430. Phytopathology 76:93-96. Accepted for publication 7 August 1985. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1986. DOI: 10.1094/Phyto-76-93.

Winter wheat cultivars Gaines, Nugaines, and Luke have durable adult-plant, temperature-sensitive resistance to Puccinia striiformis. Parental, F1, F2, and backcross populations from reciprocal crosses between these resistant cultivars and reciprocal crosses between each resistant cultivar and a susceptible line (PS-279) were evaluated in the field for rust intensity in 1982. F2 rows were evaluated for resistance as measured by rust intensity at three locations in 1984. Estimations based on three quantitative formulas indicated that rust intensity was controlled by two or three genes in Nugaines and Luke. A qualitative analysis based on the proportion of resistant F3 progeny indicated that resistance in Gaines. Nugaines, and Luke was determined by two genes, and that Gaines and Nugaines have one locus in common. Gaines and Nugaines probably have different alleles at the second locus, since there was no transgressive segregation in the Nugaines x Gaines cross. Because of the assumptions in these formulas, these estimates are for the minimum number of genes involved. Based on the very low estimates of the number of resistance genes in the Luke x Nugaines and Luke x Gaines crosses and on transgressive segregation for both resistance and susceptibility in the F2 generation, the genes in Luke differ from those in Gaines and Nugaines. Progeny with enhanced levels of resistance should be useful sources of durable resistance for breeding programs.

Additional keywords: durable disease resistance, effective factors, horizontal resistance, nonspecific resistance, partial resistance, polygenic inheritance.