Biochemical and Physiological Characteristics of Mutant Genotypes in Rice (Oryza sativa L.) Contributing to Salinity Tolerance Indices

Salinity is the most prevalent abiotic stress faced by plants. Crop improvement can be achieved using genetic diversity. Therefore, this study aimed to identify relative salinity tolerant varieties among five rice mutant genotypes, which were screened between 100 genotypes through fundamental germination and seedling evaluations. The experiment was conducted as split-plot arrangement based on a randomized complete block design with four replications. The treatments consisted of salinity levels (0, 45, 75 mM) as the main plot and mutant genotypes (Tarom Hashemi1 (TH-1), Tarom Hashemi2 (TH-2) and Tarom Hashemi3 (TH-3), Tarom Chaloosi (TC), and Nemat (N)) as subplots. Thirty-day-old rice seedlings were transferred to the plots. One week later, all genotypes were exposed to salinity stress. There has been a positive and significant correlation between shoot dry weight, catalase, and guaiacol peroxidase; in contrast, a significantly negative correlation was observed between shoot dry weight and malondialdehyde. The chlorophyll a and carotenoid contents significantly reduced under salinity, except for TC; while proline, catalase content, and root Na+/K+ ratio increased in all rice genotypes. The lowest and the highest malondialdehyde content was recorded in TC and TH-1 under 75 mM, respectively. Overall, more salt-tolerant plants showed osmotic adaptation mechanisms by activating antioxidant enzymes, whereas MDA increased in sensitive cultivars. Furthermore, principal component analysis based on salinity tolerance indexes distinguished that TC could be a more tolerant genotype compared with others. Overall, this salt-tolerant genotype could be selected to develop salt-tolerant rice varieties with high yields in the future.