Diversity among and within wild populations of Origanum syriacum collected from Jordan

Origanum syriacum L. (common name Za’atar) is a wild growing medicinal plant in Jordan and the Middle East, while Origanum majorana L. is a native plant of Cyprus and south Turkey. In this research collecting missions were conducted in different agroecologies in Jordan which allowed the sampling of 14 wild populations of O. syriacum L. In addition, four cultivated O. syriacum L. accessions and two accessions of O. majorana L. were obtained from farmers and local market. The collected material was evaluated during the 2007-08 and 2008-09 growing seasons. The obtained results indicated significant differences between different populations/accessions for all the studied characters with an overall diversity value of (H′=0.897) using Shannon Wiener diversity index. Cluster analysis clearly differentiated between O. syriacum L and O. majorana L. and also between the cultivated accessions and the wild populations. Essential oil content significantly varied between the growing seasons and the evaluated genetic material. In the second season, the essential oil per cent content among wild O. syriacum populations ranged from 1.86 to 2.60%, while for cultivated O. syriacum (1.85 to 2.13%), whereas the O. majorana accessions contained the least essential oil (1.34 and 1.41%).