Foliar Application of Salicylic Acid Enhances the Endogenous Antioxidant and Hormone Systems and Attenuates the Adverse Effects of Salt Stress on Growth and Yield of French Bean Plants

Salicylic acid (SA) is one of the strongest candidates to be used as a salinity moderator. A hydroponic experiment was conducted to evaluate the effect of foliar application of SA (0.00, 0.75 and 1.50 mM) on growth, productivity, and some physiological and biochemical parameters of French beans (Phaseolus vulgaris L.) continuously exposed to three NaCl levels (0, 50 and 100 mM). NaCl treatment significantly reduced vegetative growth parameters (between 16-50%), membrane stability (10-15%), relative water content (25-31%), chlorophyll content (21-42%), macro- and micronutrient levels (13-52% and 4-49%, respectively), growth promoters (auxins, gibberellins, and cytokinins; 11-28%), and yield of green pods (22-39%), while the phenolic compounds contents (35-55%), total antioxidant capacity (34-51%), proline (60-100%) and malondialdehyde (18-51%) contents, peroxidase activity (35-41%), Na+ (122-152%) and Cl- (170%) ions and abscisic acid (20-30%) contents were significantly increased compared to the non-salt-stressed controls. Foliar application of SA at 0.75 mM was able to overcome the adverse effects of NaCl stress to variable extent, which allowed for close to 90% of the yield of control plants to be reached. In conclusion, this study demonstrated that foliar spraying of SA helped to reduce the harmful effects of NaCl stress on French bean via regulation of some physiological and biochemical processes. This could be the basis of an effective and low-cost strategy to cope with salt stress.