| Wheat cultivars Cappelle Desprez, Druchamp, Hybrid 46, Minister, Nord Desprez, Stephens, Vilmorin 23, and Yamhill have been postulated to have resistance genes at the Yr3 locus and/or the Yr4 locus. Seedlings of parents and F1, F2, and BC1 progeny from reciprocal, diallel crosses among the cultivars and of the eight cultivars with Chinese 166 were tested for resistance to selected North American races of Puccinia striiformis. Yamhill has three resistance genes. Each of the other cultivars has two genes. No common loci were detected for crosses of Hybrid 46 with Druchamp, Minister, or Stephens and of Yamhill with Stephens. Minister, Cappelle Desprez, Druchamp, Nord Desprez, and Stephens have genes at the Yr3 locus, and the gene at the Yr3 locus in Minister is different from the gene at the Yr3 locus in the other cultivars. Hybrid 46, Vilmorin 23, and Yamhill have genes at the Yr4 locus, and the gene in Hybrid 46 is different from the gene in Vilmorin 23 and the gene in Yamhill. The second gene in Hybrid 46 is not at the Yr3 locus. Therefore, the stripe rust resistance gene Yr2 is in Yamhill; gene Yr3a is in Cappelle Desprez, Druchamp, Stephens, and Nord Desprez; gene Yr3b is not in Hybrid 46 as previously reported; gene Yr3c is in Minister; gene Yr4a is in Cappelle Desprez, Vilmorin 23, and Yamhill; and gene Yr4b is in Hybrid 46. Additional resistance genes that have not been previously named were detected in Druchamp, Stephens, Nord Desprez, Vilmorin 23, Yamhill, Minister, and Hybrid 46 and are provisionally designated as YrDru, YrSte, YrND, YrV23, YrYam, YrMin, and YrH46, respectively. Expression of dominance or recessiveness of the resistance genes in many of the cultivars were different depending upon race and genetic background. Various epistatic interactions were observed. Differences in stripe rust resistance were observed in some reciprocal crosses, which strongly suggested the existence of maternal or cytoplasmic effects on stripe rust resistance, and that the effects could be attributed to specific cytoplasm interactions with the genotype. |
