Genetic and Environmental Drivers of Drought and Heat Stress Adaptation in Mediterranean Maize Landraces

: Mediterranean maize germplasm represents an important source of genetic diversity for improving adaptation to drought and heat stress, which are increasingly limiting maize productivity under climate change. This study evaluated 213 Mediterranean maize landraces together with 10 checks, for a total of 223 genotypes, across eight contrasting environments in Tunisia and Italyto investigate vegetative growth and flowering responses under stress conditions. Key traits, including plant height (PH), days to tasseling (DT), days to silking (DS), and anthesis–silking interval (ASI), were analyzed using variance analysis, GGE biplot, and factorial regression models incorporating environmental covariates. Significant genotype (G), environment (E), and genotype × environment interaction (G × E) effects were observed for all traits, highlighting strong phenotypic variability and differential genotype responses across environments. Environmental factors explained most of the variation in plant height (51%), followed by G × E interactions (32%) and genetic effects (16%). Water availability, cumulative growing degree days (ΣGDD), and temperature were the main drivers of vegetative growth, whereas stress conditions (heat and water deficit) negatively affected plant height and increased ASI, leading to reduced flowering synchrony. Genetic groups showed distinct adaptive patterns. Corn Belt Dent (G4) and Northern Italian (G5) groups exhibited superior vegetative growth, while Southeastern Spanish (G2) and South-central Italian (G3) groups demonstrated good vegetative growth under stress. Factorial regression revealed that interactions between environmental covariates and genotypes, particularly ASI_ENV and hydric deficit (DHC) with G2, G3, G4, and G5, played a major role in explaining adaptation, emphasizing the importance of genotype-specific stress responses. Overall, this study highlights the combined influence of genetic structure and environmental factors in shaping maize adaptation to Mediterranean stress conditions and identifies promising genetic resources for breeding programs targeting drought and heat tolerance.