Nano-SiO2 seed priming improves salinity tolerance in chili (Capsicum frutescens L.) by maintaining ion homeostasis and antioxidant redox balance

Soil salinity is a major abiotic constraint limiting crop establishment and productivity, particularly in salt-sensitive crops such as chili (Capsicum frutescens L.), where early growth stages are highly susceptible to ionic imbalance and oxidative stress. This study investigated whether seed nano-priming could enhance salinity tolerance in chili. Seeds were subjected to non-priming, hydro-priming, or nano-priming (nano-SiO2, nano-chitosan, ZnO nanoparticles, or nano-selenium) for 12, 24, or 48 h and evaluated under 0 or 50 mM NaCl. Germination percentage and mean germination time were used to identify effective treatments under salinity. Salinity markedly reduced germination and delayed emergence in non-primed seeds, whereas nano-priming alleviated these effects. nano-SiO2 (300 mg L-1) and nano-chitosan (100 ppm) applied for 24 h were the most effective treatments and were selected for further evaluation in pot experiments. Under saline conditions, non-primed plants showed reduced growth, lower relative water content, increased membrane damage, and decreased chlorophyll content. In contrast, nano-primed plants, particularly those treated with nano-SiO2, maintained better growth, improved water status, reduced electrolyte leakage, and higher pigment retention. These responses were associated with reduced Na+ accumulation, improved K+ retention, higher K+/Na+ ratios, lower oxidative damage, and enhanced antioxidant enzyme activities. These findings indicate that nano-priming improved salinity tolerance in chili through coordinated regulation of ion balance and antioxidant defence.