• AM fungi
• Stevia rebaudiana

Stevia rebaudiana Bertoni is well known because it accumulates, in its leaves, ent-kaurene diterpenoid glycosides, namely steviol glycosides (SVglys), that are non-caloric natural sweeteners, possessing a 250-300 times higher sweetening property than sucrose. Furthermore, stevia leaves contain others important compounds, such are sterols, triterpenoids, essential oils, polyphenols (flavonoids and hydroxycinnamic acids), vitamins, alkaloids, water-soluble chlorophylls, xanthophylls, that can explicate antioxidant and biological activities with potential beneficial effects on human health. In the European market, the introduction of SVglys as food additives, with a purity of more than 95%, was given only at the end of 2011, thanks to the positive opinion issued by EFSA, on their safety, raising the acceptable daily intake (ADI) of 4 mg/kg BW/day, expressed as steviol equivalents (Reg. EU 1131/2011).Whereas dried stevia leaves approval in Europe must pass through the legislative procedure of the regulation on novel foods (Reg. EU 2283/2015). Arbuscolar mycorrhizal fungi (AMF) are soil-borne mutualistic fungi belonging to the phylum of Glomeromycota, that can improve plants growth rate, pathogens resistance, water and mineral nutrient uptake. Thus, these soil-dwelling symbiotic microorganisms are useful for agriculture and for cultivation of medicinal plants, stevia included. There is a crescent interesting for AMF, as agro-system providers able to sustain crop productivity and quality. In fact they are efficient when nutrient availability is low and when nutrients are bound to organic matter and soil particles. Especially for phosphorus uptake in low P soil and plants under stressed environments.
This thesis aims to evaluate the effect of AMF symbiosis and phosphorus fertilization on stevia plants. 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. Rhizoglomus intraradices has been used as inoculum. Aboveground and belowground samplings have been done at 69, 89 and 123 days after transplanting (DAT) for quantifying root colonization by AMA, the main biometric and productive characteristics, N and P uptake at 123 DAT, SVglys yield and characterization, phenols and flavonoids content, the antioxidant activity assessed by different assay.
The results achieved showed as stevia can be successfully colonized by R. intraradices and how both AMF and P fertilization can enhanced the yield and improve phytochemical profile of the stevia leaf extract. AMF symbiosis could represent a valid biofertilization strategy to improve biomass in stevia, even if it was not possible to define a clear trend for all the analysed parameters.