Effect of Water Stress on Productivity and Essential Oil Content and Composition ofThymus carmanicus

Thymus carmanicus Jalas is an aromatic and medicinal plant endemic to semi-arid regions of Iran. Studying the growth, productivity, and essential oil of this species under different water regimes is necessary to optimize its cropping techniques. Therefore, a field experiment was conducted to evaluate the effect of 20, 50 and 80 % soil water depletion on stuided traits during 2010-2011. Reduced irrigation (from 20 % to 80 % of soil water depletion) caused a decrease of the dry weight (61 %), essential oil production (42 %), and irrigation water use efficiency based on dry weight (38 %). Twenty one essential oil components were identified representing 97.2-99.8 % of the total essential oil content. The main essential oil components were carvacrol (60.1-70.4 %), thymol (6.5-13.1 %), gamma-terpinene (1.4-8.6 %), borneol (4.2-8.5 %) and rho-cymene (3.6-5.0 %). Decreased irrigation (from 20 % to 80 % of soil water depletion) reduced carvacrol (8 %) and gamma-terpinene (22 %), while increased essential oil, thymol and borneol content (45 %, 48 % and 17 %, respectively). The results showed that for maximum oil production, this species should be irrigated based on 20 % soil water depletion. Besides, from the obtained results and taking into account that carvacrol is the main component that defines the quality of this species, T. carmanicus produced good essential oil yield and content under field condition suggesting domestication of this species is possible.