Salinity stress effects on morphological traits and salt-responsive gene expression in gamma-irradiated rice mutant lines (Oryza sativa L. var. indica)

Rice is a vital crop that feeds about two-thirds of the global population and plays a critical role in food security in countries such as Costa Rica. Salinity stress, however, severely limits rice productivity. Mutation breeding, particularly through gamma radiation, is effective for developing salt-tolerant varieties. In this study, embryogenic calli of Oryza sativa L. var. indica (CR-5272) were irradiated with 40 Gy of gamma rays and regenerated into M3 mutant lines. These were screened for salt tolerance under 150 mM NaCl using both in vitro and hydroponic systems. Morphological differences, especially in root development, differentiated tolerant and sensitive mutant lines. To assess molecular responses, we analyzed the expression of four salt stress-associated genes—CYSB, SAMDC, SAMS, and HKT2—previously reported as markers of salinity tolerance. Gene expression analysis via qRT-PCR revealed contrasting expression profiles of the selected salt-responsive genes in foliar and root tissues, distinguishing tolerant mutants from control plants. This study demonstrates the utility of combining gamma irradiation with molecular screening to identify promising salt-tolerant rice lines. Our findings contribute to the development of improved cultivars and support the use of known genetic markers to monitor stress responses in mutant populations.