Effects of Salicylic and Ascorbic Acid Applications on Growth, Biomass, and Physiological Responses of Tomato Seedlings under Salt Stress

This study investigated the effects of salicylic acid (SA) and ascorbic acid (AA) applications on the growth and physiological performance of tomato (Solanum lycopersicum L.) seedlings in order to evaluate their potential to mitigate the adverse effects of salt stress. The experiment was conducted under 100 mM NaCl-induced salt stress conditions and consisted of eight treatment groups including single and combined foliar applications of SA and AA at different concentrations (1 mM and 2 mM). Plant height, stem diameter, root length, leaf number, leaf area, total fresh and dry weight, and SPAD values (chlorophyll content) were assessed. The results indicated that salt stress significantly suppressed all morphological and biomass-related parameters; however, SA and AA applications alleviated these negative effects to varying extents. The most pronounced positive effect was observed with the combined application of 2 mM salicylic acid (SA) and 2 mM ascorbic acid (AA). Compared with the salt-stressed control, this treatment increased plant height by 100.4%, total fresh weight by 60.8%, and leaf area by 61.2%, resulting in the highest biomass performance among all treatments. In contrast, the sole application of salicylic acid exhibited more limited effects, particularly on dry weight and leaf development. Chlorophyll content showed a dose-dependent response, with the low-dose combination (1 mM SA + AA) being more effective in preserving chlorophyll, whereas higher doses were associated with lower SPAD values. Overall, these findings demonstrate that the combined foliar application of 2 mM SA and 2 mM AA represents an effective, practical, and promising strategy for improving the performance of tomato seedlings under salt stress conditions.