Effect of Priformospora indica inoculation on biological activity of Stevia rebaudiana plants treated with selenium nanoparticles

Introduction:

Stevia rebaudiana Bertoni is a herbaceous plant from the family Asteraceae and used as a valuable sweetener in food industry and as anti-inflammatory, antioxidant, antipyretic, anti-fungal, and antibacterial agent in medicine and pharmacology. Piriformospora indica is an endophytic fungus, which is mainly used to improve plant growth and the amount of secondary metabolites. Selenium (Se) as an micronutrient increases the antioxidant properties and plant growth and its nano form (SeNPs) is considered as a synthetic antioxidant. To evaluate the effect of Piriformospora indica inoculation and selenium nanoparticles foliar application at two concentrations of 5 and 10 mg/l on biological activities of the methanolic extract of the regenerated S. rebaudiana plants, an experiment was conducted in 2020 in Plant Physiology Research Laboratory of the Bu-Ali Sina University of Hamadan in a factorial arrangement based on completely randomized design with three replications. 

Materials and Methods:

To investigate the effects of endophytic fungus P. indica and SeNPs application, in vitro regenerated Stevia plantlets were inoculated with P. indica and foliar sprayed with SeNPs at two concentrations of 5 and 10 mg/l. Plant samples were harvested at vegetative and initial flowering stages and used for further analyses. After measuring the growth parameters, total phenol content and antioxidant activity were evaluated by Folin-Ciocalteu and DPPH radical scavenging assays, respectively. In addition, antibacterial activity of the plant methanolic extracts was studied by disc diffusion method. 

Results and Discussion:

Inoculation of P. indica and application of SeNPs together resulted in plant growth improvement and also increase in total phenol content and antioxidant activity of the Stevia plants especially at vegetative stage. In addition, the studied extracts represented good antibacterial activity against two gram-positive bacteria, Bacillus thuringiensis and Staphylococcus aureus, and one gram-negative bacterium, Escherichia coli. The highest antioxidant and antibacterial activities were observed in the Stevia plants inoculated with P. indica and also treated with SeNPs. 

Conclusion:

Regarded to the results of the present study, P. indica inoculation and SeNPs application could result to the benefits in Stevia plants. Hence, it can be concluded that the biotic and non-biotic elicitors of P. indica and SeNPs can improve the antioxidant and antimicrobial activities of the Stevia plants by increasing the amount of total phenolic compounds.