Relation of genes for resistance to stem rust in Triticum aestivum 'Agent' and 'Agrus' to ones previously designated in eight tester lines

Abstract

The reactions of Fâ‚‚ seedlings to culture 111-SS2 (race 111) of Puccinia graminis f. sp. tritici were studied in 53 of 72 possible crosses of four 'Agent' X 'Little Club' and five 'Agrus' X Little Club derived lines of wheat with eight near-isogenic tester lines. Failure of the male to shed pollen in one Agrus derived line and unsuccessful attempts to obtain simultaneous flowering among other lines increased the difficulties in obtaining seed set. As a result, some attempts were not successful. Each Agent and Agrus derived line had been concluded previously to have a single gene for resistance to culture 111-SS2. The eight tester lines, each having a single (Sr) gene for resistance, were C.I. 14163 (Sr6), C.I. 14165 (Sr7b), C.I. 14167 (Sr8), C.I. 14177 (Sr9d), C.I. 14171 (Sr11), C.I. 14175 (Sr16), C.I. 14173 (Sr16), and C.I. 14179 (Sr18). One Agent derived line had a gene for resistance that was either the same, allelic, or closely linked to Sr9d of C.I. 14177. Two of the Agent derivatives were not tested for allelism to Sr8 because of failure to obtain crosses. From the remaining 29 crosses, 21 digenic ratios and 8 trigenic ratios expected of independently segregating genes were observed. Since the eight trigenic ratios occurred exclusively, and without exception, in crosses involving a single Agent derived line, it was concluded that the line had two genes for resistance (Tests conducted at the USDA Cereal Rusts Laboratory, University of Minnesota, indicated that one of the genes in the Agent derivative was Sr10). ...