The simultaneous effect of chitosan-plus and arbuscular mycorrhizal fungi on herbage yield, quantity and quality of spearmint (Mentha spicata L.) essential oil under an organic farming system

The essential oil (EO) from spearmint (Mentha spicata L.) is widely used as a raw material in pharmaceutical, food, and cosmetics industries. Present study investigates the effects of the foliar spraying of chitosan-plus and inoculation with arbuscular mycorrhizal fungi (AMF) under an organic farming system on the herbage yield, EO content, and carvone concentration of spearmint over two consecutive years (2019 and 2020). Interaction effect of the inoculation of AMF and foliar application of chitosan-plus significantly improved the fresh and dry weights, as well as the EO content and yield of M. spicata. In addition, a positive correlation was observed between the experimental treatments and the amounts of the root mycorrhizal colonization and P concentration. Carvone, cis- and trans-dihydrocarvone, limonene, dihyrocarveol acetate, and beta-caryophyllene were identified by GC-FID and GC-MS, representing 96-99% of total EOs. The interactive effect of the inoculation with AMF x chitosan-plus foliar application significantly influenced the percent of these constituents, with the highest carvone percentage, as the dominant constituent and an important natural product with various biological activities, detected in the EOs of the mint plants inoculated with AMF under the foliar-spraying of chitosan-plus. Overall, the use chitosan-plus along with inoculation of AMF appears to be effective in improving both the qualitative and quantitative features of the EO of M. spicata in organic farming system under normal condition and experiments related to abiotic stresses in the future.