Foliar and root applications of salicylic acid alleviate salinity stress by modulating morpho-physiological and biochemical aspects in tomato (Solanum lycopersicum)

Salinity stress is considered lethal for successful crop production under the threat of climate change. The objective of this study was to compare the efficacy of different application methods of salicylic acid (SA) for alleviating the salinity stress in tomato (Solanum lycopersicum Mill. var. BARI Tomato-4). In this study, tomato plants were exposed to salt (S, 100 mM NaCl), with the SA (1 mM) treatment applied via root pretreatment (R), foliar treatment (F), or their combined form (R + F) and without NaCl or SA (C, control). Salinity stress significantly decreased the morphological traits such as height of plants, SPAD value, fresh and dry mass of shoot and root, potassium, calcium, magnesium, sulphur, ascorbic acid (AsA), and leaf relative water content compared to control plants. On the contrary, sodium content of both the leaf and root, proline, leaf soluble sugars, hydrogen peroxide (H2O2), malondialdehyde (MDA), catalase (CAT), and ascorbate peroxidase (APX) activities were significantly increased under the saline condition than control. Applying SA improved the growth and other traits of tomato plants that suffered from salinity. Moreover, foliar treatment in combination with root pretreatment significantly increased leaf soluble sugar, proline content, CAT, and APX activities, whereas leaf and root sodium concentration, H2O2, and MDA contents were decreased compared to plants that only received salt stress treatment. The results of this study validated the beneficial effect of SA in enhancing salt stress tolerance. Despite notable variance across the various methods of SA treatment, the current findings suggest that combined foliar and root applications of SA can enhance the salt tolerance of tomato plants.