Essential oil variation in Iranian Ajowan (Trachyspermum ammi (L.) Sprague) populations collected from different geographical regions in relation to climatic factors

Ajowan (Trachyspermum ammi) is an industrial medicinal plant with different food and pharmaceutical applications. Essential oil yield and composition of 24 ajowan populations in different locations of Iran was investigated. The essential oil content of populations ranged from 1.68% in Yazshah to 5.55% in Yazd. According to GC-MS analysis, thymol (48.84-61.44%), γ-terpinene (26.96-19.46%) and p-cymene (15.09-20.32%) were the major components. According to hierarchical cluster and principal component analyses, two chemotypes were determined for Iranian ajowan populations, including high thymol, and high γ-terpinene and p-cymene groups. The highest correlation coefficient was between β-pinene and α-pinene (+0.709), while the highest negative correlation was between γ-terpinene and thymol (−0.896). In the present study, the climatic and soil orders of studied populations were determined. Canonical correspondence analysis (CCA) was also applied to assess the impact of geographic variation and environmental conditions on chemical variability of ajowan. Finally, it can be suggested that high essential oil and thymol content (phenolic chemotype) can be obtained in poor, undeveloped, relatively stony and shallow soil orders in arid and semi-arid conditions, while none phenolic ones needs higher humidity and soil depth that the first group.