Additive effects of arbuscular mycorrhizae and TiO2 nanoparticles on growth and essential oils enhancement of peppermint

Peppermint is an important medicinal plant, particularly regarding its high essential oil (EO) content. The present study assesses the effects of two Arbuscular mycorrhiza fungi (AMFs) and three concentrations of Titanium dioxide nanoparticles (TiO2 NPs) (i.e., 100, 150, and 200 mg L−1) on growth characteristics, EO constituents, phenolic content and anti-oxidative enzymatic activities of peppermint. Applying a mixed treatment of Glomus intraradices and TiO2 NPs (150 mg L-1) enhanced peppermint's shoot-fresh and dry weight by 69% and 158%, respectively, compared with controls. Also, membrane stability index (MSI) and leaf relative water content (RWC) exhibited a maximum enrichment of 69.85% and 39%, respectively, over control. Some other plant physiological characteristics were also positively affected by applying either the single or combined treatment of G. intradices and TiO2 NPs (150 mg L−1). In this regard, total phenolic content increased by 300%, DPPH radical scavenging ability by 164%, catalase by 103%, and ascorbate peroxidase activities by 124% in mixed treatment of Glomus intraradices and TiO2 NPs (150 mg L−1). Moreover, AMF symbiosis and the implementation of TiO2 NPs intervention augmented the amount of peppermint EO compounds such as menthol, menthyl acetate, and 1, 8 cineole. The highest amount of menthol production (52.04%) was obtained by adding a mixture of G. intraradices and TiO2 NPs (150 mg L−1), which had more positive effects on the other studied characteristics. Overall, AMF symbiosis and TiO2 NPs application seem suitable for promoting plant growth, improving antioxidant activity, and incrementing major components of EOs in medicinal plants. •Total phenolic contain in both AM and NM plants significantly increased with the application of TiO2 NPs.•The production of essential oil was significantly affected by the implementation of AM fungus and TiO2 NPs.•AM fungus and TiO2 NPs application had positive effects on growth characteristics and DPPH-scavenging activity.