Powdery Mildew and Aphid Resistance in Wheat–Thinopyrum intermedium Derivatives from Zhong Backgrounds

A total of 159 wheat–Thinopyrum intermedium derivatives, originating from six Zhong partial amphiploids, were evaluated for resistance to powdery mildew (Blumeria graminis f. sp. tritici) at both seedling and adult-plant stages, as well as for field resistance to wheat aphids, together with key agronomic traits. Adult-plant resistance to powdery mildew was common across three years: 34 lines (21.4%) exhibited stable resistance, and 27 (17.0%) were moderately resistant. Resistance frequencies differed among pedigree backgrounds, with Zhong 2 & 5 derivatives showing the highest proportion of stable resistant lines (35.7%). Seedling resistance was detected in 63 lines (39.6%). Aphid resistance was less frequent, with 61 lines (38.4%) classified as resistant, including two highly resistant lines derived from Zhong 3 and Zhong 1 & 3 backgrounds. Combined resistance traits were comparatively rare. Thirty-two lines exhibited resistance to powdery mildew at both seedling and adult-plant stages, while nine lines displayed combined resistance to seedling mildew, adult mildew, and aphids. Analysis of agronomic traits indicated that environmental effects accounted for a substantial proportion of the observed phenotypic variation, whereas pedigree background and resistance responses contributed comparatively little. Correlation analyses revealed generally weak associations between resistance responses and agronomic traits, suggesting that resistance was not a major determinant of agronomic performance within the evaluated population. The identified resistant materials, therefore, represent valuable pre-breeding resources for the incorporation of resistance to multiple biotic stresses in wheat. Further genetic characterization and multi-environment evaluation will facilitate their effective utilization in wheat improvement programs.