Morpho-physiological and ionic trait-based multi-index integrative salt tolerance assessment of rice genotypes from Pokkali and pan-Indian saline ecologies

Salinity stress imposes severe limitations on rice productivity, necessitating a mechanistic dissection of tolerance traits for robust identification of elite donors. We collected an extensive array of 335 genotypes from the inland and coastal saline tracts in India. The salinity tolerance potential of the diverse rice germplasm was evaluated at the seedling stage under moderate (8 dS m⁻¹) and high (12 dS m⁻¹) stress levels. A systematic trait-based screening was carried out using 13 morpho-physiological and 7 ionic parameters under control and two stress levels. Subsequently, salt tolerance indices (STI) calculated from the recorded traits were subjected to principal component analysis, which displayed near-identical correlation across both stress levels. It was observed that biomass traits clustered together and diverged from linear growth traits. Using the principal component traits thus identified, mean membership function values (MMFV) and Multi-trait genotype–ideotype distance index (MGIDI) were deployed for integrative tolerance ranking of genotypes. Regression analyses converged on root and shoot K⁺/Na⁺ ratios, and shoot dry weight as the most robust predictors of salt tolerance. Consequently, the developed ‘SalTol Reg’ model was reiterative in predicting a comprehensive salt tolerance index such as MMFV. Integration of multiple selection indices identified four previously unreported novel salt tolerant landraces, namely Neta, Arjunsal, Chovvaryan and Orthadiyan. These genotypes demonstrated superior biomass traits, tissue-specific Na + exclusion and enhanced selective K + translocation over Na + to shoot tissues. Unravelling the molecular physiology underlying their tolerance will be a prudent step towards delivering promising salt tolerant donors. • An integrative multi-index multi-trait framework enabled a robust assessment of seedling stage salinity tolerance across 335 diverse rice genotypes. • Adoption of three indices, namely TSTI, MMFV and MGIDI resulted in discrete classes of genotypes under moderate and severe salt stress. • SK/Na, RK/Na, and SDW emerged as the most reliable trait predictors of seedling-stage salinity tolerance, validated through correlation and regression modelling. • The developed ‘SalTol Reg’ model forms a strong statistical framework for evaluating salinity tolerance. • The novel salt tolerant landraces - Neta, Arjunsal, Chovvaryan and Orthadiyan exhibited enhanced biomass accumulation, photosynthetic stability and ionic balance.