Effects of plant-growth-promoting rhizobacteria and arbuscular mycorrhizal fungus on plant growth, stevioside, NPK, and chlorophyll content of Stevia rebaudiana

Stevia rebaudiana Bertoni is a unique medicinal plant which is mostly utilized as a sugar substitute for diabetic patients. In this research, regenerated plantlets of stevia in tissue culture is transferred to pots in greenhouse and inoculated with plant-growth-promoting rhizobacteria (PGPRs) (Bacillus polymixa, Pseudomonas putida, and Azotobacter chroococcum) and arbuscular mycorrhizal fungus (AMF) (Glomus intraradices). The results showed that in comparison to control, inoculation with a single microorganism, significantly increased root and shoot biomass as well as stevioside, chlorophyll, and NPK content in plants. However, such increased effects have been found to be further enhanced significantly due to dual compatible mixtures of inoculants resulting from their strong synergistic relationships among themselves. All growth parameters recorded the highest in 60-days-old plants in the treatment of Glomus + Azotobacter and followed with Glomus + Bacillus and Azotobacter + Pseudomonas treatments, respectively. Furthermore, high-performance liquid chromatography (HPLC) chromatograms revealed that the highest stevioside content have been produced in same treatments. Triple treatments had less positive effects compared to dual inoculations. Probably competence between microorganisms in triple inoculations has reduced their efficiency. Thus, suitable combination of mycorrhizal fungi and PGPR as biotic elicitors can enhance growth and stevioside content in tissue culture-regenerated plantlets of stevia.