Impact of Arbuscular Mycorrhizal Fungi (AMF) and Phosphorus Fertilization On Stevia (Stevia rebaudiana Bertoni) Growth, Yield and Steviol Glycosides.

This study aims to evaluate the effect of Arbuscular Mycorrhizal Fungi (AMF) symbiosis and phosphorus fertilization on stevia growth, yield and steviol glycosides (SVglys) content and composition. Six treatments have been compared in a pot trial, testing three phosphorus doses (0, 25 and 50 mg P2O5/kg of soil) in plants with and without AMF (control). Rhizoglomus intraradices has been used as inoculum. Aboveground and belowground samplings have been done at 89 and 123 d after transplanting (DAT) for quantifying the main biometric characteristics, plant biomass and SVglys. R. intraradices successfully established mycorrhizal symbioses, with root colonisation above 75 % in inoculated plants. At both sampling dates, mycorrhizal inoculation influenced plant height and branch number, independently of P level, with AMF-treated plants characterised by lower stem height and increased branching. At 123 DAT, inoculated plants showed a leaf dry yield higher than control (+16 %). On the other hand, stem dry yield and below-ground biomass were not significantly influenced by AMF, while P fertilization seemed to be the main factor affecting their production level. A clear effect of AMF was evident in leaf SVglys content and composition at 89 DAT, with highest values in AMF-treated plants. Interestingly, in all P-treated plants Dulcoside A and Rebaudioside B could be detected, but not in control leaves. In plants harvested at 123 DAT, AMF positively influenced the total SVglys content only of treated plants grown without phosphorus (0P). Anyway, at 123 DAT, AMF-treated plants showed the highest yield (g plant-1) of Stevioside, Rebaudioside A and C, as a consequence of the enhanced leaf production. In conclusion, this study showed that AMF symbiosis could represent a valid biofertilization strategy to improve biomass in stevia, since AMF, in association with P supply, increased stevia leaf production and SVglys content, even if it was not possible to define a clear trend for all the analysed parameters.