Evaluation of Changes in Essential oil of Ajowan (Trachyspermum copticum L.) Ecotypes under Drought Condition

Ajowan (Trachyspermum copticum L.) is one of the most important herbs of the Apiaceae family in semi-arid tropical regions of Iran, which is considerable in the production of essential oils with valuable secondary metabolites, especially thymol. In order to determine the secondary metabolites profile of ajowan under drought stress, a split plots experiment was conducted in two irrigation conditions (normal and drought stress) as main factor and 36 ecotypes of ajowan belong to 9 different provinces of Iran as sub plots were planted based on a randomized complete block design with 3 replications during 2015 and 2016 in Agricultural Jahad Research Station of Kerman. Based on the results of combine analysis, water stress has significant effect on the components of essential oil. Gas chromatography–mass spectrometry (GC–MS) analysis revealed the presence of 13 compounds with the major constituents including thymol, p-cymene and γ-terpinene constituents in all ecotypes in both irrigation conditions. Based on bi-plot, two groups of high thymol and high p-cymene were identified. In this experiment, increasing the irrigation interval effected as an advantageous strategy to improve pharmacological component in some ecotypes. In conclusion, Zabol ecotype was superior to others, in terms of its relatively good performance of thymol, special in drought stress and it is recommended as suitable ecotype for cultivating in dryland and also where drought stress usually happens at the end of cropping season. Also, two ecotypes included Zabol and Mohammadieh were identified as extreme ecotypes in response to drought stress in reproductive stage, these ecotypes could be recommended for breeding programs to obtain drought tolerant thymol-chemotype cultivars ajowan.