Response of morphophysiological parameters and antioxidants system of stevia (Stevia rebaudiana Bertoni) medicinal plant to inoculation of Piriformospora indica under cadmium stress

In order to investigate the role of Piriformospora indica endophyte fungi on some vegetative, physiological and morphological parameters along with antioxidant activity of stevia (Stevia rebaudiana) under cadmium (Cd) stress, an in vitro experiment was conducted. Experiment arranged in completely randomized design with three replicates. Treatments were five levels of Cd (0, 5, 10, 15 and 20 mg/L from cadmium chloride source) and two levels of fungi inoculation (including control and inoculation with P. indica). After 30 days, some growth characteristics, photosynthetic pigments, antioxidant enzymes activity, electrolyte leakage and soluble protein were measured. Regression analysis indicated that among vegetative dry weights, stem dry weight in uninoculated plants showed the maximum sensitivity (76%) to Cd concentration gradients. Fungi inoculation, however, markedly improved root dry weight up to 57%. Among morphological parameters, leaf area showed the highest reduction when Cd increased in the growing medium. By contrast, where P. indica was inoculated, green leaf percentage (51% reduction) was the most tolerant parameter. In terms of photosynthetic pigments, fungi inoculation could ameliorate reduction of carotenoid and chlorophyll a/b contents from 77 and 37 to 40 and 11%, respectively. In conclusion, results of the present study indicated that P. indica inoculation particularly at lower Cd concentrations could relatively improve stevia tolerance throughout decreasing H2O2 accumulation and enhancing photosynthetic pigments.