Assessing Salinity Tolerance in Rice (Oryza sativa L.) Mutant Genotypes (M3) with Emphasis on Stress Tolerance Indices in Seedling Stage

Salinity stress is one of the most severe constraints limiting rice production worldwide. Thus, the development of salt-tolerant rice can provide increasing food demand due to climate change effects.

To investigate the reaction of mutant genotypes to salinity stress in the seedling stage, 309 selected mutant genotypes selected in the third generation along with Hashemi local cultivar and FL478 (resistant) in two levels of NaCl salinity (0 and 10 dS/cm) were evaluated as a completely randomized factorial design with two replications. Growth parameters like root length, shoot length, root fresh and dry weight, shoot fresh and dry weight and plant biomass were measured after 14 days of exposure to two levels of stress namely, non-stress (EC ~ 1.2 dS/m) and saline stress (EC ~ 10 dS/m) in hydroponics at seedling stage. The Stress tolerance index (STI), Stress susceptibility index (SSI), Mean productivity (MP), Stress tolerance (TOL) and Geometric mean productivity (GMP) for each genotype was calculated for all the traits.

The results of analysis of variance showed a significant difference between genotypes for all traits that indicated genetic diversity between them. A wide range of genetic variability was observed among genotypes for studied traits that root traits were identified as the best descriptors for tolerance to salt stress conditions. Results of correlation coefficients among the indices showed that STI, HMP and GMP indices were the most suitable resistance indices. Salt stress response indices (SSRI) were used to classify the number of 144 mutant genotypes; 25 mutant genotypes (17.4%) were identified as salt-sensitive, 46 (32.6%) with Hashemi parent in salt-sensitive group, 41 (32.6%) with FL478 each in salt-tolerant group, and 30 (20.8%) as highly salt tolerant. Among the mutant genotypes, four mutant genotypes em3hs290, em3hs292, em3hs165 and em3hs84 were identified as the most tolerant genotypes based on stress tolerance indicators, minimum leaf tubing, high biomass rate and better stress compensation ability. Also, the mutant genotype em3hs31 was introduced as the most sensitive genotype with a minimal performance at the stress level.

Induced mutation of EMS has desirable effect on creation of salinity tolerant mutant genotypes and the studied indices can utilize for separating of salinity tolerant mutant genotypes in rice mutant populations. This mutant population could serve as a valuable genetical resource in the development of novel salt-tolerant varieties for the salinity prone regions under rice cultivation.