Genotype x environment interaction for stomata traits in a rice recombinant inbred population

Drought is a major abiotic constraint limiting global rice ( Oryza sativa L.) production. While stomatal traits are linked to drought adaptation, their environmental stability and breeding utility are poorly understood. This study evaluated 272 recombinant inbred lines (RILs) derived from an IRRI 154/NERICA 4 cross under well-watered and reproductive-stage drought-stress conditions across four seasons (2022WS - 2024DS) to quantify genotype-by-environment (G×E) interactions for four stomatal characteristics (density, area, length, and width) on both leaf surfaces. Significant genotypic variation and pronounced transgressive segregation were observed for all traits. While reproductive-stage stress reduced mean grain yield by 84.6%, stomatal density remained numerically stable across moisture regimes. Conversely, cell dimensions exhibited high plasticity, driving a 20.5% reduction in abaxial stomatal area and a 17.2% reduction in length to facilitate rapid closing kinetics. Combined multi-environment analysis revealed that while raw grain yield heritability dropped to 0.39 under stress due to seasonal masking, abaxial stomatal density and area preserved exceptionally robust combined heritability (H 2 , 0.92 and 0.99, respectively). Stomatal traits displayed weak direct correlations with final grain yield, indicating they function as upstream components of stress resilience rather than direct drivers of sink capacity. Crucially, these findings demonstrate that breeders can focus exclusively on abaxial stomatal density under well-watered conditions as a unified, high-heritability proxy for large-scale germplasm screenings. This operational shortcut captures baseline genetic variation while completely avoiding stress-induced leaf deformations, offering a highly scalable, high-throughput pathway to accelerate climate-resilient rice development.