Plant growth, mineral nutrition and volatile oil composition of Mentha suaveolens subsp. timija (Briq.) Harley cultivated under salt stress conditions

Mentha suaveolens subsp. timija is a strict Moroccan endemic species that is intensively exploited from the wild because of its wide ranging medicinal and culinary properties. This has resulted in the species becoming rare or threatened with risk of extinction in the wild. In order to ensure the conservation and sustainable utilization of this valuable medicinal and aromatic plant, its cultivation has been suggested as a promising solution. However, many uncontrolled factors can affect this cultivation including salinity. Thus, the present work aims to evaluate the effects of saline conditions simulated by different NaCl concentrations (0, 50, 100 and 150 mM) on growth (fresh and dry weights), mineral content, essential oil (EO) quantity and quality of M suaveolens subsp. timija. The experiment was conducted inside a shade house at the experimental garden at the Faculty of Sciences, Semlalia-Marrakech during the growing season (February–May) of the year 2010. The results showed that increasing NaCl levels to 150 mM reduced significantly the fresh and dry biomass production by 47.558% and 69.324%, respectively, in comparison to the control. Application of NaCl induced also an increase in Na⁺ content, while K⁺ content and K⁺/Na⁺ ratio decreased with increasing salt stress. The EO yield decreased by 38.9% and 50.6% at 100 and 150 mM NaCl, respectively, compared with the control (0.77 ± 0.14%). Pulegone, menthone and isomenthone were found to be the principal components of M suaveolens subsp. timija EO. The relative abundance of menthone in particular was affected by salt stress. Based on the present results, it can be concluded that mint timija is a salt sensitive crop and cannot be cultivated in salt-affected areas.