Alkaline stress is an important abiotic constraint limiting rice productivity in many agricultural regions worldwide. Elevated soil pH negatively affects nutrient availability, chlorophyll biosynthesis, photosynthesis, and overall plant growth. The present study investigated the morphological responses of six rice genotypes (BR-4, BRRI-7, BRRI-40, BRRI-55, BRRI-67, and BRRI-78) grown under control and alkaline stress (pH 7.8) conditions for six weeks under greenhouse conditions to identify genotype-dependent variation in alkaline stress tolerance. In this study, alkaline stress significantly affected plant performance in several rice genotypes, although the magnitude of stress-induced reduction differed among genotypes. Significant decreases in chlorophyll score and growth-related parameters were observed in sensitive genotypes, indicating severe physiological disruption under alkaline conditions. In contrast, BRRI-67 and BRRI-78 maintained comparatively higher chlorophyll retention and biomass accumulation under stress conditions, suggesting improved stress adaptation mechanisms. Statistical analysis revealed significant treatment effects in multiple physiological parameters. The observed variation among rice genotypes demonstrates the importance of genetic background in regulating alkaline stress tolerance. Tolerant genotypes likely maintained better nutrient acquisition, chlorophyll stability, and physiological homeostasis under alkaline environments. The findings may provide useful germplasm for mechanistic studies on alkaline stress tolerance and may contribute to breeding programs aimed at improving rice productivity in alkaline soils.
