Gene Action in Wheat Cultivars for Durable, High-Temperature, Adult-Plant Resistance and Interaction with Race-Specific, Seedling Resistance toPuccinia striiformis

Stephens and Druchamp wheat (Triricum aestivum) cultivars have both durable, high-temperature, adult-plant (HTAP) resistance and race-specific, seedling resistance to stripe rust caused by Puccinia striiformis. Gene action for the HTAP resistance was studied in parental and F 1 , F 2 , and backcross populations from reciprocal crosses among Stephens, Druchamp, Paha (a cultivar with race-specific resistance), and Michigan Amber (a susceptible cultivar) using stripe rust intensity data from the field transformed to area under the disease progress curve (AUDPC). Based on a joint scaling test, the additive component for HTAP resistance was significant for both Stephens and Druchamp. When HTAP resistance was effective and seedling resistance was ineffective in the same parent, the dominant component and the additive-additive, additive-dominant, and dominant-dominant epistatic interactions contributed significantly to HTAP resistance in Druchamp but not in Stephens. When HTAP resistance and seedling resistance were effective in the same parent, the dominant component and additive-additive and dominant-dominant epistatic interactions were significant in both Stephens and Druchamp and the additive-dominant epistatic interaction was significant in Stephens but not in Druchamp. When HTAP resistance was effective in one parent and seedling resistance was effective in the other parent, the dominant component and the additive-additive and dominant-dominant epistatic interactions were significant in the Druchamp crosses but not in the Stephens crosses. When HTAP resistance was effective in both parents, the additive and dominant components were detected at the Mount Vernon, WA, site but not the Pullman, WA, site. A constant cytoplasmic effect and a cytoplasm-dominance interaction were significant in reciprocal crosses of Stephens with Paha inoculated with race CDL-29; HTAP resistance was greater when Stephens was the female parent. A cytoplasmadditive gene interaction was significant in the reciprocal crosses of Druchamp with Paha tested with race CDL-25. Based on the gene action of HTAP resistance and its interactions with seedling resistance, it should be possible to exploit both HTAP and seedling resistances in breeding programs and in crosses; Stephens and Druchamp should be used as female parents to obtain the highest HTAP resistance