Optimization of Essential oils production in Mentha longifolia L. using plant growth promoting cyanobacteria

Background: The cyanobacteria isolated and purified from soil can increase plant growth and productivity as bioelicitors. Objective: This study aimed was to investigate the effect of cyanobacteria as a bioelicitor on the production efficiency and essential oil composition of Mentha longifolia L. Methods: Two species of heterocystous cyanobacteria, Anabaena vaginicola ISB42 and Nostoc spongiaeforme ISB65, were used as bioelicitors to optimize the growth and productivity of Mentha longifolia L. Five pots were considered for each treatment and five others for the control plants. Treatment lasted for 100 days, and the treated plants were irrigated with 200 ml of cyanobacterial suspensions (0.2 %) every 21 days intervals. The experiment was performed in a randomized complete block design in an experimental greenhouse condition. After inoculation of treated plants with cyanobacterial bioelicitors, the vegetative factors, including shoot and root length, leaf area, as well as fresh and dry weight of plants were evaluated. In addition to growth factors, analyses of essential oils in studied plants were performed. Results: The results showed significant improvement in vegetative growth indices of the treated plants. Also, some economic and medicinal metabolites such as menthol, eucalyptol and phytol were increased in the essential oil of treated plants. The results also showed a significant increase in sesquiterpene hydrocarbons and oxygenated diterpenes in plants treated with cyanobacteria compared to controls. Conclusion: So, the use of cyanobacterial bioelicitors can be suitable to increase the yield as well as the economic and medicinal value of this medicinal plant.