Yield and quality of essential oils of Mentha arvensis in response to inoculation with arbuscular mycorrhizal fungi

The objective of this work was to evaluate the effects of different species of arbuscular mycorrhizal fungi on the vegetative growth, production and composition of essential oil of Mentha arvensis L., grown in different phosphorus levels. The work was carried out under greenhouse conditions and a randomized block design was used with 20 treatments, constituted by the combination of five microbiological treatments (Glomus clarum Nicolson & Schenck, Glomus etunicatum Becker & Gerdemann, Gigaspora margarita Becker & Hall, Acaulospora scrobiculata Trappe and control) and four P levels (0, 50, 100, 200 mg kg(-1)), with four repetitions. Plants were harvested 65 days after transplanting. Results showed that, when no phosphorus was added, Gigaspora margarita and Glomus clarum increased, in 206% and 198%, respectively, the fresh matter production of shoots, compared to the control treatment. The highest fresh matter production (90 g por pot) was observed in plants inoculated with A. scrobiculata at 133 mg kg(-1) of phosphorus. When phosphorus was not used, the essential oil content and menthol levels in the oil were smaller in plants not inoculated, and the inoculated treatments provided increments of up to 89% in the essential oil and menthol contents in relation to treatment not inoculated. No increment in essential oil and menthol contents occurred when the doses of P were increased. The highest essential oil and menthol production, 0.69 g and 0.48 g for pot, respectively, were found in plants inoculated with A. scrobiculata at the P levels and 126 and 123 mg for kg of soil, respectively.