Phytochemical response of Stevia plant to growth promoting microorganisms under salinity stress

Stevia (Stevia rebaudiana Bertoni) is a salt-sensitive herb with sweet leaves without side effects for diabetic patients. The present research was conducted to investigate the effect of endophytic fungus Piriformospora indica and two bacterial isolates, namely of Streptomyces sp. (kj152148) and (kj152149) with Stevia host plants. These microbial isolates were utilized as growth-promoting agents for induction of salt stress tolerance and secondary metabolite accumulation in inoculated plants. The present experiment was designed as factorial basis experiment based on a completely randomized design with six replications undertaken in two consecutive years (2016-2017). Treatments included three levels of salinity [0.85 (control), 1.5 and 3 dS/m] and four levels of plant growth-promoting microorganisms [no-inoculation, Piriformospora indica, Kj152148 Streptomyces sp (S1) and K152149 Streptomyces sp (S2)]. Under stress and non-stress conditions, endophytic fungus and bacterial isolates had significant positive effect on the recorded biochemical and physiological parameters of stevia. Inoculation of fungus and bacterial isolates reduced the negative effects of salinity stress by increasing antioxidant enzymes and free radical scavenging activity, phenol and flavonoid accumulation and total glucose and proline concentrations. From the results it may be concluded that, indicated a positive effect of applied fungus and bacterial treatments on the resistance of stevia plant to the salinity stress and due to the relative susceptibility of stevia to salinity, pre-treatment of the plant using of the desired microbes is recommended before planting in soil areas susceptible to salinity. (c) 2020 SAAB. Published by Elsevier B.V. All rights reserved.