Study the physiological and biochemical properties of peppermint (Mentha pipertis L.) in response to salt stress and coexistence with Piriformospora indica fungi

In Iran, salinity extension of soils along with high levels of salinity of water limit quality of product and productivity. Since, in the recent years global demand for the use of medicinal herbs such as peppermint is increasing, nowadays the use of microorganisms that have a symbiotic relationship with plants is a new strategies to improve the environmental performance of the plants in adverse conditions such as saline water and soil. In this study, therfore, the effect of symbiotic mycorrhiza like fungi, Piriformospora indica on growth improvement of peppermint was designed and implemented under salt condition. The experiment was at conducted at Genetics and Agricultural Biotechnology Institute of Tabarestan at Sari the Agricultural Sciences and Natural Resources University in factorial arrangement based on randomized complete block design with three replications in 2015. Two factors including P. indica symbiosis and uninoculated control and four salinity levels (irrigation and distilled water and the Caspian Sea water mixture at of 0, 3, 6 and 9 dS. m-1). The parameters were studied such as leaf dry weights, root colonization, root length, lipid peroxidation, ion leakage, total phenol content of leaves, flavonoids, anthocyanins and the antioxidant enzymes activity (catalase, superoxide dismutase, and polyphenol oxidase, radical scavenging DPPH) were measured. Results showed that with increasing salinity the root colonization, leaf dry weight and root length decreased, while catalase, superoxide dismutase, and polyphenol oxidase, radical scavenging DPPH, total phenol content of leaves, flavonoids, anthocyanins, lipid peroxidation and ion leakage were increased. There was a significant correlation (r= 0.95**) between antioxidant activity and phenol content, as a result, the plants showed with high phenolic compounds, they have higher than the radical anti-radical activity. The symbiotic fungi improved plant dry weight, root length, phenolic compounds and antioxidant enzymes. Biological treatment also reduced the negative effects of salinity on membrane peroxidation and cell membrane stability, and also induced better the activity of antioxidant enzymes in saline conditions. Generally the P. indica inoculated plants performed better than the non-inoculated plants in terms of growth performance, but this increase was affected by salinity levels. In addition, the use of P. indica, not only stimulate the plant to increase the synthesis of phenolic compounds, but also developed the root system by fungal hyphae resulted in alleviating the effect of salinity in the peppermint. Therefore, it seems that p. indica could induce salt tolerance and roughly improve growth parameters of peppermint plants.