Plant growth, steviol glycosides and nutrient uptake as affected by arbuscular mycorrhizal fungi and phosphorous fertilization in Stevia rebaudiana Bert

The increasing demand for products based from Stevia rebaudiana Bertoni (both leaves and purified steviol glycosides) makes of interest the research on sustainable production systems, in order to guarantee secure availability and high quality of agricultural raw materials. Arbuscular mycorrhizal fungi (AMF) symbiosis represents an interesting tool for increasing crop production and quality, especially thanks to improved nutrient absorption, particularly phosphorus (P). In the present study, Stevia rebaudiana Bert. plants were exposed to different levels of P fertilization (0, 25 and 50 mg P₂O₅kg⁻¹ soil) with or without Rhizoglomus irregulare inoculation, in order to evaluate root colonization, plant growth and productive parameters, steviol glycosides (SVglys) yield, as well as nitrogen (N) and P concentrations and uptake. A nutrient balance was also carried out and the nutrient use efficiency was evaluated. Stevia roots were highly colonized by Rhizoglomus irregulare, especially in the absence of P fertilization. During the whole vegetative growth, the AMF symbiosis, in association with the P supply, benefitted stevia growth, especially with regard to leaf dry biomass production and SVglys yield. Arbuscular mycorrhizal fungi symbiosis was able to modify the growth habit of stevia plants, with increased branching and a reduced plant height. At the end of the vegetative growth, mycorrhizal plants reached the highest leaf dry yield, together with the highest SVglys production. The application of 25 mg P₂O₅kg⁻¹ soil in association with AMF symbiosis seemed to be the most effective treatment in improving stevia SVglys yield and P uptake together with P nutrient use efficiency.