Alleviation of the adverse effects of NaCl stress on tomato seedlings (Solanum lycopersicum L.) by Trichoderma viride through the antioxidative defense system

Background: Species of Trichoderma are widely recognized for their biocontrol abilities, but little information regarding their mechanisms in promoting plant growth and enhancing its tolerance to salt stress are available. Salt stress is one of the main abiotic stresses restricting crop growth and productivity. Hence, this study aimed to investigate the NaCl effects on Trichoderma viride growth as well as on the seedlings morphological, physiological, and biochemical parameters of tomato ( Solanum lycopersicum L.). Besides, the role of T. viride in promoting tomato seedling stress tolerance was scrutinized. Results: : Results showed that 100 mM NaCl decreased the colony diameter of T. viride by 13.4 % compared to the control. Exposure of tomato seedlings to salt stress resulted in an overall decrease in growth, relative water content (RWC), and protein contents. At the same time, increases were found in proline, H 2 O 2 content, malondialdehyde (MDA), as well as the activities of peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), and ascorbate peroxidase (APX). Even though, with T. viride application, the salt negative effects were mitigated to a greater extent. Moreover, T. viride increased proline and total antioxidant capacity (TAC) in tomato seedlings at 100 mM NaCl by an average of 20.66 and 43.82 % compared to their comparable control. T. viride increased the activities of CAT, PPO, and APX enzymes by 74.6, 58.48, and 61.61% at 50 mM NaCl compared to non-saline control seedlings. As well, T. viride decreased MDA and H 2 O 2 contents by an average of 14 and 24.8 % in tomato seedlings at 50 mM NaCl compared to their comparable control. Conclusion: Hence, our study provides new insight into the mechanisms of T. viride that can activate both enzymatic and non-enzymatic antioxidant defense systems and enhance tomato seedling tolerance to salt stress at morphological and physiological levels.