Genetic relations among and within wild and cultivated Thymus species based on morphological and molecular markers

In the present study, the diversity of 11 Thymus species was assessed using molecular and morphological markers. Essential oil content and morphological traits were also investigated during two agronomic years. The result of the analysis of variance showed considerable differences among morphological traits. In the first and second years, the essential oil content of the species varied from 0.63 to 1.94% and 0.86 to 2.34%, respectively. T. vulgaris and T. migricus showed the highest essential oil content in two agronomic years. In this research, nine ISSR primers were also used to amplify 151 polymorphic bands in 77 accessions belonging to 11 Thymus species. Cluster and principal component (PCA) analyses classified the species in three major groups. Among the species, T. vulgaris and T. fedtschenkoi presented relatively higher genetic distance in comparison with other species. Analysis of molecular variance (AMOVA) revealed that 72.34% of the total variation was belonged to within-species variation, while 27.66% was associated among the species. High gene flow (Nm = 1.11) and genetic differentiation (Gst = 0.31) were also observed among the species. T. transcaspicus exhibited the highest genetic variation (0.19), polymorphism % (57.69%), and Shannon index (0.29). The STRUCTURE analysis also showed a high admixture of Thymus species that might be originated from a high rate of natural hybridization. Finally, based on molecular and morphological information, T. vulgaris and T. carmanicus can be suggested as good candidate species for further breeding programs in Thymus species.