Identification of low-light-tolerant rice (Oryza sativa L.) genotypes based on agro-morphological traits, combined stress tolerance and stability index

Abstract

Low light is a major abiotic stress during the wet season, leading to an approximate 35% reduction in rice yield compared to the dry season. Developing rice varieties with improved yields and tolerance to low light conditions is therefore critical. This study aimed to identify low-light-tolerant rice genotypes using a Combined Stress Tolerance and Stability Index (CSTSI). A panel of 192 genotypes was evaluated for 12 agro-morphological traits during the Kharif (wet) seasons of 2021 and 2022. Results showed that low light significantly reduced key traits such as tiller number, grain number, spikelet number, spikelet fertility, panicle number, grain weight, biomass, and grain yield. Two-way ANOVA indicated significant genotypic variation under low light stress, with grain yield and biomass reductions of 41.96 and 28.49%, respectively. Yield Stability Index (YSI) and Relative Yield (RY) were calculated to assess genotype performance. The CSTSI was developed to evaluate overall stress tolerance among the 192 genotypes. Regression analysis revealed strong correlations of CSTSI with RY (0.897) and YSI (0.791), confirming its effectiveness in identifying low-light-tolerant genotypes. Based on the CSTSI, nine genotypes were identified as highly tolerant, outperforming the tolerant check variety, Swarnaprabha. Cluster analysis grouped the 192 genotypes into five clusters. Clusters IV and V included tolerant genotypes such as Purnandu, Ambika, Laxmichura, Chamarmani, Bhasamanik, TRB-468, VL Dhan209, Swarnaprabha, and TRB-451, which exhibited superior performance in YSI, RY, and CSTSI. In contrast, cluster I contained low-performing genotypes like Kunti, Sanwal Basumati, IR8, IR64, Pusa-834, Srabani, Sahabhagi Dhan and Khandagiri. Identifying low-light-tolerant genotypes provides valuable insights for identifying QTLs, genes, and superior haplotypes associated with low-light tolerance. These findings are critical for molecular breeding programs aiming to develop resilient rice varieties for low-light environments. Additionally, the study establishes CSTSI as a reliable parameter for screening genotypes for low-light tolerance.