Abstract
Rice (Oryza sativa L.), is an important cereal crop fulfilling half of the world's food demands, is the most salt-sensitive among cereals. Approximately 30% of rice growing areas in the world are harmfully affected by soil salinity which is a major threat for global food security. High osmotic potential in rhizosphere and high sodium uptake is generally regarded as the main causative factor for reduced growth and yield. Rice genotypes exhibit variability in sodium uptake and osmo-regulation processes. The role of proline is widely documented as an osmoprotectant and controversial for enhancing salt tolerance in crop plants. In the present study eighteen rice genotypes were studied for physiological and agronomical traits under hydroponically controlled saline conditions (6 dS/m NaCl) at flowering and maturity stages. Significant differences were observed for genotypes, treatments and their interactions for evaluated traits. This study revealed negative correlation of proline and sodium with grain yield under salinity. While highly significant positive correlation (r= 0.800) between sodium and proline suggest over production of proline under salinity stress is sodium dependant. Hierarchical cluster and nearest neighbor relative analysis corroborated the salinity induced physiological responses of genotypes, revealed physiological traits based genetic similarity of genotypes and classified into tolerant and sensitive groups. The genotypes Kharaganja, Shua-92-155/E and RST-177 were found relatively tolerant at 6 dS/m NaCl in term of good yield with medium sodium and low proline. High proline producing genotypes (GML-529, GML538, HHZ5-SAL-10-DT2-DT1 and GML-534) yielded less or no grain weights. Based on these results proline over production under salinity may be regarded as an indicator of stress.
