Arbuscular Mycorrhizal Fungi Mitigates Salt Stress Toxicity in Stevia rebaudiana Bertoni Through the Modulation of Physiological and Biochemical Responses

Salinization of soil is a major problem affecting many plant physiological processes. The use of arbuscular mycorrhizal fungi (AMF) plays a key role in improving the growth and the crops yield. The aim of this study was to evaluate the combined effects of salt stress and AMF on agro-physiological and biochemical responses of Stevia rebaudiana Bertoni. The experiment was carried out in a completely randomized design with ten replicates under the green house conditions. Stevia plants were inoculated with AMF consortium (MC) or with Rhizophagus irregularis (Ri) on the presence (80 mM of NaCl) or the absence (0 mM of NaCl) of salt stress. The results showed that plant height, dry biomass of shoots and roots parts, mycorrhizal frequency and intensity, relative water content, chlorophyll fluorescence, stomatal conductance, chlorophyll a, and total chlorophyll were significantly reduced by 29%, 72%, 36%, 84%, 65%, 24%, 17%, 60%, 28.50%, and 40.9% respectively under salt stress. These changes were associated with a significant increase in antioxidant enzymes (activity of polyphenol oxidase, peroxidase, superoxide dismutase, and catalase), electrolyte leakage, lipid peroxidation, and hydrogen peroxide contents. The application of AMF (MC and Ri) improved growth and physiological parameters through rising the activities of antioxidant enzymes and reduction of the oxidative damage caused by the salt stress. The better results were recorded with MC-inoculated plants. These findings suggested that AMF could be an effective strategy to alleviate the adverse effects of salt stress on Stevia rebaudiana.