Effect of the bio-fertilizers on the steviol glycosides (SGs) content and biomass in Stevia rebaudiana (Bert.) Bertoni at vegetative and flowering stages

Stevia rebaudiana Bertoni is a unique medicinal herb mostly utilized for substitution of the sugar, producing zero-calorie sweeteners known as steviol glycosides (SGs), including stevioside (ST), rebaudioside A (RA), rebaudioside F (RF), rebaudioside C (RC) and dulcoside (DU). While bio-fertilizers have been demonstrated to enhance the production of secondary metabolites in many plant species, their effects on S. rebaudiana have not been thoroughly studied. This paper presents a study on the effects of bio-fertilizers and their interactions on modifying and improving the SGs content and biomass production in S. rebaudiana at two growth stages, vegetative and flowering. Vermicompost (V) and cow manure (M) (as soil amendments), and garden soil (S) were used separately, and also in combination to fill pots. In this research two factors included cultivation bed [S (control), SM (garden soil + 15 % cow manure + 0% vermicompost), SMV10 (garden soil + 15 % cow manure + 10 % vermicompost), and SMV20 (garden soil + 15 % cow manure + 20 % vermicompost) by %weight in pots (w/w)], and fungi application (two species of fungi Funneliformis mosseae (Fm), Serendipita indica (Si) inoculation and without fungi inoculation) were investigated on the percent, yield of SGs and biomass at vegetative and flowering stages. The percentage and yield of total SGs, SGs elements [(ST, RA, RF, RC, DU, and RA/SGs ratio] and aerial dry biomass of S. rebaudiana were significantly affected by all treatments and their interactions (P < 0.01). Generally, the highest SGs elements percentage was obtained in the control plant at the vegetative and flowering stages (S). Also, the highest SGs yield was observed in SMV20Fm in both vegetative and flowering stages. Funneliformis mosseae, in combination with SMV20, had shown significant effects on RA/SGs ratio, SGs yield, and plant aerial dry biomass in vegetative and flowering stages.