Stability and adaptability of current common wheat cultivars for grain yield under the conditions of Southern Dobrudzha

Over a period of six consecutive growing seasons (2020-2025), grain yield (GY) performance of thirty-five winter wheat genotypes developed at the Dobrudzha Agricultural Institute, General Toshevo, during the last three decades was evaluated. The study aimed to assess the productivity, stability and adaptability of modern Bulgarian wheat varieties under the agro-ecological conditions of Northeastern Bulgaria in a situation of several seasonal meteorological anomalies. Grain yield data (t ha⁻¹) were obtained from field plots with an area of 12.5 m², arranged in a randomized design with three replications. All cultivars were grown under identical agronomic management practices. Sowing was performed annually between 15 and 25 October at a seeding rate of 500 viable seeds m⁻². Yield data were subjected to multi-environment statistical analyses to quantify the effects of genotype (G), environment (E; year), and their interaction (G×E), and to evaluate cultivar stability and adaptability. The growing seasons differed substantially with respect to grain yield formation, providing a robust basis for objective assessment of cultivar performance. Environmental conditions, genotype, and their interaction had a highly significant effect on grain yield. The G×E interaction accounted for approximately 20% of the total phenotypic variation, while the combined contribution of genotype and G×E explained nearly half of the overall variability in grain yield. The interaction effect was complex and multi-dimensional, with several principal components (PC1-PC5) contributing significantly, indicating heterogeneous cultivar responses to seasonal conditions. The application of multiple statistical models and complementary analytical approaches to unbalanced multi-environment data enabled effective discrimination among cultivars based on realized grain yield and stability. The combined use of established stability indices and integrated ranking approaches facilitated the identification of cultivars with superior performance in terms of productivity, stability, and adaptability. Among the most valuable cultivars under the conditions of Southern Dobrudzha were Kami, Kosara, Roki-3, Radoslava, Korona, Yulita, Fani, Kiara, Kalina, and Lazarka.