Yield Performance, Stability, and Adaptability of the Elite Wheat Cultivar Zhoumai 49 in Multi-Environment Trials: Combined Evidence from GGE Biplot, WAASB, and Eberhart–Russell Analyses

Multi-environment evaluation of yield performance and stability is essential for the rational recommendation of new cultivars. This study evaluated the elite winter wheat (Triticum aestivum L.) cultivar Zhoumai 49—a third-generation descendant of the founder parent Zhou 8425B—using national trial data from the southern Huang-Huai irrigated wheat region: the 2020–2021 and 2021–2022 regional trials (18 cultivars at 23 and 22 locations; checks Zhoumai 18 and Zhoumai 36) and the 2022–2023 production trial (8 cultivars at 22 locations; check Zhoumai 36). The aims were to quantify the relative contributions of genotype, environment, and genotype-by-environment interaction to grain yield, to assess the yield performance, stability, and adaptability of Zhoumai 49 relative to the check cultivars within the national testing system, and to dissect the yield component mechanism underlying its high yield. Variance decomposition, genotype plus genotype-by-environment interaction (GGE) biplot, weighted average of absolute scores (WAASB) and yield-integrated WAASBY indices, Eberhart–Russell regression, path analysis, genotype-by-trait (GT) biplot, and random forest approaches were combined. Environmental effects accounted for 76.2–92.7% of the yield variation, with entry-mean heritability of 0.90–0.94. Zhoumai 49 ranked 2nd and 1st in mean yield in the two regional trial years (8720.6 and 9897.6 kg ha−1), outyielding the two checks by 7.33–9.31%, and ranked 1st in the production trial (8752.1 kg ha−1; +6.98%). Its WAASBY ranked 1st, 1st, and 3rd across the three years; the Eberhart–Russell coefficients (b = 1.011–1.056) with non-significant deviations in the regional trials indicated an average-responsive, widely adapted type with high responsiveness under favorable production conditions. Kernels per spike was the core advantage trait (Z = 1.20–1.69; random forest importance = 0.514), showing inter-annual compensation with the other components. Zhoumai 49 is recommended for medium-to-high-fertility irrigated fields in the southern Huang-Huai region.