Colonization of Satureja hortensis L. (Summer savory) with Trichoderma harzianum alleviates salinity stress via improving physio-biochemical traits and biosynthesis of secondary metabolites

Salinity as the main abiotic stress, influences plant growth, yield, and productivity, especially in arid and semi- arid areas of the world. Researchers are increasingly turning to biological strategies to improve crop tolerance to high salinity levels, such as using endophytic fungus. This study aimed to evaluate the morphological, physio- logical, and biochemical responses of Summer savory (Satureja hortensis L., Lamiaceae) plants to inoculation with Trichoderma harzianum (an endophytic fungus) under various levels of salinity (0, 50, 100, and 150 mM NaCl) in a pot-based experiment. The results showed that Summer savory inoculated with T. harzianum exhibited improved growth compared with salt-stressed and non-stressed plants (up to 93.47%). Furthermore, inoculation with T. harzianum caused a restoration in the content of chlorophyll a, b, and carotenoids up to 1.47-fold. Both non-enzymatic and enzymatic antioxidants were enhanced in the presence of salt stress, and T. harzianum further increased their level, approximately up to 66.67%. Salinity caused an obvious increase in hydrogen peroxide, malondialdehyde, and electrolyte leakage (up to 3.04-fold), but their content began to decline when the plants were inoculated with T. harzianum (with reduction factor up to 41.43%). Additionally, T. harzianum-inoculated plants maintained higher levels of proline, total soluble sugar content (up to 1.46-fold), and volatile organic compounds compared with control and salt-stressed plants. Overall, the findings of this study suggest that inoculation with T. harzianum can enhance the salt tolerance of S. hortensis by improving growth via modulation of biochemical, physiological, and secondary metabolites biosynthesis. Therefore, T. harzianum may be a promising biological strategy for improving crop productivity under saline conditions.