Salinity tolerance of two rice cultivars is related to enhanced activities of enzymatic antioxidants and higher proline content

Soil salinity leads to reduced plant health and productivity necessitating the need for salt-tolerant crop cultivars. Thus, the present study evaluated the salinity-induced modulations in morphological, physiological and biochemical responses of two popular rice cultivars bred in Bangladesh, namely BRRI dhan55, which has been developed for growing in dry and pre-monsoon season, and BRRI dhan43, developed for pre-monsoon season. The rice cultivars were exposed to different levels of salt stress (0–300 mM NaCl) after seedling establishment under natural sunshine. Salinity posed a significant growth decline in both the rice cultivars. Under increasing salinity stress, BRRI dhan43 exhibited a pronounced reduction in overall growth. Chlorophyll and proline content declined significantly in BRRI dhan43 with rising salt concentration. A marked decrease in antioxidant enzyme activities, including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) was also observed. Furthermore, salinity severely reduced grain yield and associated yield parameters in BRRI dhan43. In contrast, BRRI dhan55 demonstrated comparatively better tolerance under salinity. Although chlorophyll content was reduced in BRRI dhan55, the decrease was less pronounced than in BRRI dhan43, while proline content increased with increasing salinity. Additionally, antioxidant enzyme activities (SOD, CAT, and APX) were increased in BRRI dhan55. However, grain yield and yield attributes in BRRI dhan55 were moderately affected by salinity, showing noticeably less reduction compared to BRRI dhan43. Results indicate that the higher salt stress tolerance of BRRI dhan55 is attributed to higher protection of photosynthetic machineries, osmolyte biosynthesis, and upregulated antioxidant functions leading to better yield performance compared to less tolerant rice cultivars.