Silicon-mediated oxidative stress tolerance and genetic variability in rice(Oryza sativa L.) grown under combined stress of salinity and boron toxicity

The benefits of silicon (Si) in improving crop fitness by biotic and abiotic stress resistance are widely reported. However,investigations about its protective mechanisms for plants facing multiple stresses are very limited. Two contrasting rice cultivars, KS-282 (salt-tolerant) and IRRI-6 (salt-sensitive), were grown in a pot experiment to study the interrelation between Si supplementation (0and 150 mg kg–1) and boron (B) toxicity (0 and 2.5 mg kg–1) under salinity stress with emphasis on growth response, mineral contents,physiology, and enzymatic antioxidant system response. The results revealed that adverse growth conditions, particularly the combinedstress of salinity and B toxicity, severely affected the physiological attributes of rice. It reduced plant biomass by damaging the membrane,reducing special products analysis division values and photosynthetic efficiency, but Si application counteracted the adverse effects ofstress by reducing the uptake of toxic ions such as sodium (Na+) and B, lowering transpiration rate. Increased relative water contents andphotosynthetic efficiency due to a higher Si and K+ uptake ultimately led to better growth performance. Si significantly affected activitiesof enzymatic antioxidants in both genotypes, with increased ascorbate peroxidase, increased guaiacol peroxidase, and reduced catalaseactivity suggesting relieved stress by reduced oxidative damage. The response to stress and Si differed genotypically, with maximumdamage to the salt-sensitive genotype (IRRI-6), particularly under the combined stress of salinity and B toxicity. In contrast, supplied Si improved the growth of the salt-tolerant genotype (KS-282) better than the IRRI-6 (salt-sensitive) genotype. These results support theprotective role of Si in the regulation of salinity and/or B toxicity stress by improving growth, K+/Na+ ratio, physiology, and antioxidantcapacity, suggesting it as a potential candidate for crops grown under such deteriorated soil conditions.