Inheritance of resistance to stem rust in six wheat lines having adult plant resistance

Abstract

Inheritance of resistance to race 15B-1 of stem rust (Puccinia graminis Pers. f. sp. tritici Eriks, and Henn.) was studied in six lines of wheat (Triticum aestivum L.) having adult plant resistance. The six lines were crossed to a susceptible line and the progenies were advanced to the F5 generation by the single seed descent method. From 91 to 135 F5-derived F7 lines from each cross were tested with race 15B-1 in field nurseries and selected lines were tested in a multirace nursery. The number of genes controlling resistance was estimated by grouping the F7 lines into those as resistant as the resistant parent and other lines, and testing against the ratios expected with various numbers of genes. In 1982, for all six crosses, the segregations fit best to either three- or four-gene ratios. The mean rust severities for the F7 lines in each cross were concentrated at the susceptible end of the distribution. Apparently the genes for resistance had small effects that were multiplicative rather than additive. Under lighter epiphytotics in 1983 and 1984, additional F7 lines were classified as resistant as the resistant parents. The F7 lines were generally more resistant to the multirace mixture than to race 15B-1. The resistant parents probably carried genes for specific seedling resistance to some of the races but in some cases may have carried additional genes for adult plant resistance.Key words: stem rust, Puccinia graminis tritici, wheat, Triticum aestivum, adult plant resistance.