The South American plant Stevia rebaudiana Bertoni is a good source of steviol glycosides, antioxidants, all of the essential amino acids, and other important nutritional compounds. The present study was conducted to investigate the effects of 5 and 10 mg L-1 concentrations of selenium nanoparticles (SeNPs) and 50 mg L-1 ancymidol (ANC) on physiological and biochemical characteristics of Stevia rebaudiana colonized by the root endophytic fungus Piriformospora indica at vegetative and initial flowering stages. Results indicated that ANC decreased root colonization rate and antioxidant enzyme activities but increased the MDA content and had no effect on the phosphorus uptake and total carbohydrate content. The adverse effects of ANC were minimized after the P. indica colonization and somewhat with SeNPs application. Our results suggest that the P. indica colonization and SeNPs application can alter the equilibrium between free radicals production and enzymatic defence reactions in the S. rebaudiana plants by enhancing the free radicals scavenging capacity and by decreasing the membrane lipid peroxidation during both vegetative and initial flowering stages. Moreover, the effects of ANC, SeNPs, and P. indica on the measured characteristics at the vegetative stage were higher than those observed at the initial flowering stage.
