Silicon (Si) application has great potential to improve salt tolerance in a variety of crop plants. However, it is unclear how Si influences the responses of contrasting rice cultivars when exposed to excessive salt. Here, we investigated the functions of Si in alleviating the negative effects of salt stress on two contrasting rice cultivars, namely BRRI dhan48 (salt-sensitive) and Binadhan-10 (salt-tolerant). Rice seedlings was pre-treated with three doses of Si (as silicic acid; 0, 1 and 2 mM) for 14 days at one-day interval before being exposed to salt stress (10 dSm−1) in a sustained water bath system. The results demonstrated that the seedlings of BRRI dhan48 and Binadhan-10, respectively exhibited substantial reductions in shoot height (16 and 9%), shoot fresh weight (64 and 43%) and shoot dry weight (50 and 39%) under salinity. Intriguingly, BRRI dhan48 pre-treated with 1 and 2 mM Si, respectively, showed a higher increase in shoot height (SH) (by 25.90 and 26.08%) as compared with Binadhan-10 (by 3 and 8%) under salt stress compared with their respective controls. Data revealed that a comparatively higher improvement in the growth performances of the salt-induced Si pre-treated BRRI dhan48 than that of Binadhan-10. For example, 1 and 2 mM of Si treatments significantly attributed to elevated leaf relative water content (RWC) (13 and 22%), proline (138 and 165%), chlorophyll a (42 and 44%), chlorophyll b (91 and 72%), total chlorophyll (58 and 53%) and carotenoids (33 and 29%), and recovery in the reductions of electrolyte leakage (13 and 21%), malondialdehyde content (23 and 30%) and shoot Na+/K+ ratio (22 and 52%) in BRRI dhan48 compared with Si-untreated control plants under salt stress. In addition, we found salt-tolerant Binadhan-10 also had enhanced RWC (9 and 19%), proline (12 and 26%) with pre-treatment with 1 and 2 mM of Si, respectively, under salt stress, while no significant differences were noticed in the case of photosynthetic pigments and Na+/K+ ratio. Our results showed that Si supplementation potentiated higher salt-tolerance ability in the salt-sensitive BRRI dhan48 as compared with salt-tolerant Binadhan-10. Thus, Si application could be highly beneficial in the growth recovery of the salinity-affected salt-sensitive high yielding rice cultivars in the saline-prone areas.

Salt stress has detrimental effects on the growth and development of rice seedlings. In the present study we assessed salt-responsiveness of three coastal rice landraces namely Nona-morchi, Kalihytta and Nara. We conducted two factors pot trial that included five rice genotypes (three candidates coastal rice landraces, Binadhan-10 as tolerant check and BRRI dhan48 as sensitive check) against three salinity levels e.g., control (tap water), 6 and 12 dSm-1 of sodium chloride. Study revealed that, at 12 dSm-1 of salinity, Binadhan-10 showed the lowest reduction in shoot length (14.62%), shoot fresh weight (30.04%) and shoot dry weight (33.71%) which was followed by Nona-morchi, Kalihytta, Nara and BRRI dhan48. Two stress tolerance indices e.g., relative water content (RWC) and electrolyte leakage (EL), also support salt-induced responses of these five rice genotypes. At the highest level of salinity (12 dSm-1), the lowest RWC reduction was observed in Nona-morchi (8.20%) which is followed by Binadhan-10 (11.38%), Kalihytta (38.93%), BRRI dhan48 (36.30%) and Nara (36.51%). And, the highest EL increased in Nara (40.06%) which is followed by BRRI dhan48 (22.06%), Kalihytta (21.12%), Binadhan-10 (8.64%) and Nona-morchi (5.87%) compared with their respective controls. Importantly, photosynthetic pigments profile (chlorophyll a, chlorophyll b, total chlorophyll) were increased in Nona-morchi (24.48, 15.22 and 21.87%, respectively) and Binadhan-10 (13.75, 12.50 and 13.41%, respectively) and reduced in Kalihytta (7.89, 19.42 and 11.08%, respectively), Nara (27.76, 31.32 and 28.76%, respectively) and BRRI dhan48 (32.73, 36.97 and 34.02%, respectively) at 12 dSm-1 salinity compared with their respective controls. It is to noteworthy that at 6 dSm-1 of salt stress, shoot length significantly decreased in the sensitive check BRRI dhan48 by 23.07%, Kalihytta by 17.32% and Nara by 11.54%. While, no significant effect of 6 dSm-1 of salt stress was observed in Binadhan-10 and Nona-morchi in case of shoot length, root length, shoot fresh and dry weight, EL and RWC . Among the three coastal rice landraces, Nona-morchi found as highly tolerant and Kalihytta were found as moderately tolerant while Nara was identified as sensitive against salt stress (12 dSm-1). In the future, these identified salt tolerant rice genotypes might be the ideal resource for breeding new salt tolerant rice varietie