Study on essential oil content and composition of Thymus caramanicus Jalas in different harvesting stages

In order to study the effects of harvesting stages on essential oil yield and composition of Thymus caramanicus Jalas, an experiment was conducted during 2007-2009 in Fozveh Research Station of Isfahan. collected seeds from natural habitat were cultivated in pots and then seedlings were transplanted at the main field in a randomized complete blocks design with 3 replications. Aerial parts of the species were harvested at 4 stages including: beginning of flowering, fifty percent flowering, full flowering and fruit set during two years. The plant materials were dried and their essential oils were obtained by water distillation. Capillary GC and GC/MS analysis were used to determine the volatile profile of essential oil samples. Results showed that harvesting stages had significant effects on thymol and carvacrol content and essential oil percentage. The highest amount of essential oil and thymol percentage were obtained at full flowering stage of the first year (1.56% and 3.59 kg/ha, respectively) and the maximum carvacrol percentage was obtained at fruit set stage of the first year (25.45 kg/ha). Six components consisted the highest amount of essential oil, among them carvacrol was dominant at all 4 harvesting stages. The highest amount of carvacrol was obtained at the beginning of flowering stage (88.45%) in the second year. Thymol was the second dominant component with a maximum percentage of 11.77%, obtained at full flowering stage. The highest content of ρ- cymene, 1,8-cineole and γ-terpinene were obtained at fruit set stage (2.35, 1.21 and 2.15%, respectively) and the highest content of borneol was recorded at full flowering stage (7.52%). Also, a positive correlation was observed between essential oil percentage and amounts of thymol and carvacrol. In conclusion, the best time for harvesting of T. caramanicus to achieve the maximum carvacrol percentage was fruit set stage, while full flowering stage was identified as the best time to achieve the maximum essential oil and thymol percentage.