Effects of NaCl on growth, essential oil and chemical composition of Plectranthus amboinicus

Plectranthus amboinicus (Lour.) Spreng. is a plant used both as spice or as traditional herbal medicine. Its cultivation is expected to grow in the future, driven by the growing interest toward nutraceuticals and alternative medicine. Mediterranean Region is amply characterized by salt irrigation water, so posing limitations to the introduction of new crops. However, if properly managed, this feature can be used to improve the secondary metabolites profile of many crops. For these reasons a greenhouse experiment was conducted to determine the effect of four NaCl concentrations in the irrigation water (corresponding to an EC of 0.4, 5, 10 and 15 dS m-1 ) on some physiological variables, as well as on essential oil content, yield and chemical composition in P. amboinicus. Saline irrigation progressively increased Na+ , Cl- and proline concentration into the plant (up to +235, +231 and +959%, respectively), highlighting a growing condition of metabolic disturbance in salt- stressed plants. Accordingly, salt stress gradually reduced P. amboinicus fresh herb and essential oil yield as compared to control plants (up to -68 and -62%, respectively). However salt-stressed plants increased their essential oil content up to 0.129% at 10dS m-1 . Thymol, ?-terpinene, p-cymene and trans-caryophyllene were the major components of P. amboinicus and the concentration of these compounds was significantly affected by salt stress. Our results show positive modifications in the essential oil composition of P. amboinicus in response to salt stress, a feature that could be properly supported by means of agronomical and breeding strategies. Key