Application of BLUP-GGE Biplot in Mega-Environment Analysis and Test Location Evaluation of Wheat Regional Trials in the Huanghuai Winter Wheat Region in China

Accurate delineation of mega-environments (MEs) and rigorous evaluation of test lo-cations are critical for optimizing regional variety trial schemes, particularly when addressing unbalanced datasets from multi-year, multi-location wheat (Triticum aestivum L.) trials. This study aimed to refine the regional wheat trial framework in the Huanghuai winter wheat region (HWWR) of China using an integrated BLUP-GGE biplot approach, which combines best linear unbiased prediction (BLUP) values with genotype main effect plus genotype-by-environment interaction (GGE) biplot analysis to account for temporal variability and experimental error. We systematically com-pared GGE biplots constructed from raw phenotypic data and BLUP values in terms of goodness of fit and their ability to resolve inter-location relationships. We further assessed test location representativeness, discriminating ability, and overall desirability via the BLUP-GGE biplot, and contrasted ME delineation outcomes between the traditional “which-won-where” polygon method and the test location clustering-based approach. The BLUP-GGE biplot explained 81.1% of total phenotypic variation, a substantial improvement over the conventional raw-data GGE biplot (62.4%). Raw-data GGE biplots exhibited highly complex inter-location correlations, distorted by unaccounted year effects and environmental noise, which hindered reliable location evaluation and ME classification. In contrast, all location vectors in the BLUP-GGE biplot displayed positive correlations (maximum angle = 83.9°), confirming the ecological homogeneity of the target region and yielding robust evaluation results. Based on the ideal tester view, ZMD was identified as the most desirable location, followed by SQU and PY, while LYG, BJ, SQ, and XY exhibited relatively poor comprehensive performance. MEs delineated by the “which-won-where” method showed strong inter-ME correlations and insufficient differentiation, whereas the location clustering-based method markedly enhanced inter-ME discrimination (maximum vector angle ≈70°), stably partitioning the HWWR into three distinct MEs with clear cultivar–ME interaction patterns: ME1 (HX, SZ, FY, SQ, LYG), ME2 (ZMD, SQU, GY, XX, HA, LH, XMQ, LY, HY, YL, PY, XZ), and ME3 (SY, YY, XY, BJ). This study confirms the superiority of the BLUP-GGE biplot for analyzing unbalanced multi-year multi-environment trial data and validates a robust clustering strategy for ME delineation. The findings provide a scientific basis for optimizing wheat regional trial systems and facilitating precise cultivar deployment in the HWWR, and offer a reference for analogous studies on other crops or ecological regions.