The effect of Piriformospora indica fungi on photosynthetic pigments and the function of antioxidant system in stevia under drought and salt stresses

In order to evaluate the effect of Piriformospora indica fungi inoculation on antioxidant systems and photosynthetic pigments of stevia medicinal plant under salt and drought stresses, an in vitro experiment was conducted. Experiment arranged in factorial based on completely randomized design with three replicates. Treatments were three levels of osmotic potential (0, -5, and -10 bar), three osmotic sources including NaCl (Na), Mannitol (M) and NaCl+Mannitol (N+M) and two levels of fungi inoculation (uninoculated control and inoculation with P. indica). Results showed that among the mentioned osmotic sources, NaCl had the most inhibitory effect on photosynthetic pigments of stevia. When M concentration increased in uninoculated plants, the enzymes activitiy such as catalase and superoxide dismotase increased too. In non-stress conditions P. indica improved photosynthetic pigments including chlorophyll a, b, a+b and carotenoids. Also, inoculation of stevia plantlets with P. indica at osmotic level of -5 bar caused by M+Na markedly improved chlorophyll b and a+b up to 41 and 57%, respectively as compared to the uninoculated control. Fungi inoculation also improved activity of antioxidant enzymes as compared to uninoculated control. Where Na and M+Na was applied to cause -5 bar of osmotic level,  superoxide dismutase activity increased by 62 and 185%, respectively as compared to the control. In conclusion, results showed a positive effect of P. indica on stevia tolerance to both salinity and drought stresses.