Effects of Growth Stimulator Microbes on Growth and Ions Concentration of Stevia under Salinity Stress Conditions

Soil salinity and water deficit are major problems for development of agricultural production. In this study, effects of growth promoting microorganisms (inoculation with Piriformospora indica and two isolates of Streptomyces sp.) on the leaf yield and absorption rate of some elements in leaves and roots of stevia plant was investigated under salinity conditions for two consecutive years (2016-2017). The fresh and dry weights of the leaves were significantly affected by microorganism and salinity. High salinity level led to sodium accumulation in the root and leaf; while the amount of potassium and K+/Na+ ratio decreased in both root and leaf. The accumulation of phosphorus in both leaf and root was significantly decreased in 3 ds m-1 salinity. Plants exposed to Piriformospora indica and Streptomyces strains, showed lower sodium content in their leaves and roots. In contrast, an increase in the content of potassium and phosphorus was observed in the growth stimulator microbes-treated plants. However, the K+/Na+ ratio in the growth stimulator microbes-treated plants was to some extent lower than its ratio in control plants. In conclusion, P. indica and Streptomyces strains improved the biomass formation of the stevia plant under salinity conditions by controlling the uptake of potassium, phosphorus and sodium.