HIGH-TEMPERATURE, ADULT-PLANT RESISTANCE TO WHEAT STRIPE RUST AND EFFECTS ON YIELD COMPONENTS

High-temperature, adult-plant (HTAP) resistance to stripe rust (Puccinia striiformis West) in wheat (Triticum aestivum L. em Thell) has remained durable for at least 30 yr in the USA. The expression of HTAP resistance to stripe rust in six crosses of winter wheat was evaluated using F6 populations at Pullman, WA in 1986 and F7 populations at three environmentally different locations (Pullman, Mt. Vernon, and Walla Walla, WA) in 1987. Resistant families could not be differentiated at Pullman in 1986 and Walla Walla in 1987 because unfavorable weather delayed the development of rust. Differences in rust intensity for families within each cross could be determined at Mt. Vernon and Pullman in 1987. Distributions of disease intensities for families of each cross were significantly different between the two locations. Negative correlations between three yield components (kernel number, kernel weight, and spike weight) and rust intensity at several plant growth stages were high when infection was early and rust intensity was severe, but were not significant when infection was late and rust intensities were moderate or low. Early rust development negatively affected kernel number. At Mt. Vernon, the plant growth stages at which yield components were most highly correlated with rust intensities varied depending on the cross. Most yield components were highly correlated with disease intensity at heading and milk stages. The environment at Pullman was appropriate and possibly better suited for selection of moderate or higher levels of HTAP resistance which are usually adequate for wheat grown in eastern Washington. Highly resistant families, however, could more easily be differentiated from moderately resistant families only under severe rust intensities that occurred at Mt. Vernon; thus an environment similar to Mt. Vernon is highly useful to select for the highest levels of HTAP resistance.