Citric acid nanoparticles effectively overcome the impacts of salt stress in hot pepper plants

Foliar spraying with citric acid (CA), a natural organic acid, has gained momentum in overcoming the impacts of salt stress by enhancing plant physiological and antioxidant responses, however, nanomaterials have a higher advantage in this regard. This is the first research to study the effects of foliar spray of citric acid nanoparticles (n-CA) at different concentrations (0, 0.1, 0.2, 0.3, 0.4, and 0.5 mM) on the growth, physiological responses, osmotic and antioxidant regulation, and fruit quality of hot pepper under salinity conditions (10.5 dS m–1). The results exhibit significant improvement in growth (leaf area and shoot dry weight), fruit yield, fruit quality (vitamin C and capsaicin contents), nutritional (N, P, and K) quality, K+/Na+ ratio, leaf photosynthetic pigments, osmoprotective and antioxidant compounds content, relative water content, and membrane stability index, while the levels of Na+, oxidants (superoxide and hydrogen peroxide), and oxidative damage (malondialdehyde and electrolyte leakage) decreased in response to all n-CA foliar treatments. The positive effect of treatment gradually increased with increasing n-CA concentration up to 0.4 mM and then reduced compared to the control using a concentration of 0.5 mM. Therefore, foliar spray of 0.4 mM n-CA was the best treatment as a viable agronomic strategy, which is recommended to mitigate the negative effects of salinity in hot pepper plants and enhance growth and crop quality.