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Resistance

The Relationship Between Slow-Rusting and Some Genes Specific for Stem Rust Resistance in Wheat. B. Skovmand, Former Research Fellow, Department of Plant Pathology, University of Minnesota, St. Paul, MN 55108 (now Postdoctorate Fellow at the International Maize and Wheat Improvement Center, Londres 40, Mexico 6, D. F.); A. P. Roelfs(2), and Roy D. Wilcoxson(3). (2)Research Plant Pathologist, Cereal Rust Laboratory, Agricultural Research Service, U.S. Department of Agriculture, University of Minnesota, St. Paul, MN 55108; (3)Professor, Department of Plant Pathology, University of Minnesota, St. Paul, MN 55108. Phytopathology 68:491-499. Accepted for publication 5 October 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-491.

The relationship between slow-rusting and genes for specific resistance against stem rust was studied in F₅ lines derived from diallel crosses among the wheat cultivars Idaed 59, Kenya 58, Thatcher, Lee, Marquis, Prelude, and Baart. Slow-rusting in the F₅ lines was measured in natural epidemics of stem rust and by calculating the area under the rust progress curve derived from weekly estimates of stem rust severity. Lines that possessed either the dominant or recessive allele of genes for specific resistance, Sr5, Sr6, Sr7b, Sr11, and SrTt1, were identified in a seedling test in the greenhouse using appropriate cultures of Puccinia graminis f. sp. tritici. Then the slow-rusting ability of lines possessing the dominant allele of an Sr gene was compared to the slow-rusting ability of half-sib lines possessing the recessive allele of the same Sr gene. There was no effect on the development of stem rust attributable to the recessive or to the dominant alleles of Sr5, Sr7b, and Sr11. There was an association between the development of stem rust and the dominant allele of the SrTt1 gene, but slow-rusting was not due to this allele. The genes conditioning slow-rusting may be located on the same chromosome as the SrTt1 locus and linked to SrTt1. There also was an interaction between slow-rusting and the dominant allele of gene Sr6. The F₅ lines possessing the dominant allele of Sr6 rust more slowly than the lines possessing the recessive allele. However, in the group of lines with the dominant allele of Sr6, there were some fast-rusting lines. This indicated that slow-rusting was not due to the Sr6 gene, per se, but due to associated genes for slow-rusting.