Arbuscular mycorrhizal symbiosis and phosphorus supply induce changes in photosynthetic rate, sugar partitioning and steviol glycosides composition in stevia

This study aimed to evaluate the physiological and phytochemical responses of Stevia rebaudiana to arbuscular mycorrhizal fungi (AMF) inoculation (Rhizoglomus irregulare) and P fertilization (0, 25 and 50 mg P205 kg"' of substrate). At the end of the vegetative phase, AMF colonization, growth parameters (leaf specific weight, harvest index and below-ground biomass), steviol glycosides (SVglys) concentration and composition, leaf gas exchanges, photosynthetic pigments and soluble sugar content, were assessed. The inoculated plants showed increased harvest index, reduced specific leaf weight and a significant increase of total soluble sugars and total monosaccharides in their roots. Both AMF and P fertilization had meaningful effects on stevia, modifying sugar partitioning and stimulating leaf gas exchanges. AMF x P interaction positively affected SVglys concentration and composition, shifting the pathway towards the production of rebaudioside A, B and C. So, a highest rebaudioside (A+B+C) to ste-vioside ratio was observed in all inoculated plants, to indicate an increased stevia leaf quality in terms of organoleptic properties.