Breeding progress and climate adaptation in semi‑dwarf durum wheat: Genetic gains from long‑term multi‑environment trials under a Mediterranean environment

Durum wheat is a key cereal in Mediterranean agriculture, where productivity is challenged by climate change and yield stagnation. However, information on genetic gains after the introduction of Rht genes remains limited. This study quantified breeding progress and associated trait changes using a 35-year dataset from the Italian National Variety Trials, including 223 semi-dwarf cultivars released between 1982 and 2023 and evaluated across four contrasting Mediterranean environments. Genetic effects were isolated using a linear mixed model accounting for site × year environmental variation, cultivar, and genotype × environment interaction, with genetic gain estimated as a fixed regression of each trait on cultivar year of release, fitted separately per site. Grain yield increased significantly with year of release at all sites (0.43–0.81% year⁻¹), mainly through increased grain number per unit area, partly driven by increased spike density. Grain weight showed no consistent trend. Grain protein concentration did not decline over time, indicating yield gains were not associated with a dilution effect. Heading date showed no change across year of release, suggesting modern cultivars already flower within an optimal window, while plant height showed an increasing trend. Despite rainfall and temperature shifts across the 35 years, the model's environmental term showed no significant temporal trend for grain yield at any site, indicating environmental change did not generate systematic yield variation. Overall, breeding has contributed to sustained yield improvement under Mediterranean conditions, likely also reflecting indirect selection for adaptation to changing climatic conditions, while maintaining grain quality.