Synergistic Effect of Exogenous Application of Proline and Boric Acid on the Growth, Physiological Aspects, and Postharvest Quality of Radish under Salt Stress

Salinity is one of the primary abiotic stresses that limits yield, particularly in semiarid regions, affecting the growth and physiological aspects of crops. Proline and boric acid, when applied exogenously, can improve plants' tolerance to salt stress. Therefore, this study aimed to evaluate the effect of exogenous proline and boric acid application on the growth, physiological aspects, and postharvest quality of the "Crimson Gigante" radish variety under salt stress. The research was conducted in a greenhouse using a randomized block design with a factorial scheme of 3 × 4 and four replications. The treatments were composed of three levels of electrical conductivity of the irrigation water (0.5 dS m^-1, 2.5 dS m^-1, and 4.5 dS m^-1) and four treatments with attenuating agents [control, proline (5 mM), boric acid (1 mM), and the combination of proline and boric acid (5 mM + 1 mM)]. Growth variables, gas exchange, photosynthetic pigments, and postharvest physicochemical quality were evaluated. Applying proline and boric acid improved plant growth and physiological responses under salt stress (2.5 and 4.5 dS m^-1). At 2.5 dS m^-1, proline + boric acid increased the plant height (11.96%), stem diameter (29.40%), and photosynthetic rate (19.27%). At 4.5 dS m^-1, the same combination enhanced plant height (25.69%), shoot dry mass (36.70%), and pulp firmness (30.78%). Boric acid increased chlorophyll a (19.88%) and anthocyanins (26.91%) at 2.5 dS m^-1. Proline raised flavonoids (45.05%) and anthocyanins (55.18%) at 4.5 dS m^-1. Thus, the combined application of proline and boric acid (5 + 1 mM) may be a viable alternative to mitigate the deleterious effects of salt stress in radish plants.