Morphological–Phytochemical Diversity of Some Native Thymus Populations (Thymus caramanicus Jalas) in Kerman Province

Thymus species are among the most valuable medicinal plants in Iran, with Kerman province serving as a primary natural habitat due to its diverse ecological conditions. This study evaluated the morphological and phytochemical diversity of 12 Thymus accessions collected from the natural habitats of Kerman province. The accessions were cultivated under controlled greenhouse conditions using a Randomized Complete Block Design (RCBD) with five replications. Measured parameters included plant height, fresh and dry weight yield of flowering shoots, leaf length, leaf width, number of lateral branches, essential oil (EO) percentage, and EO yield. Analysis of variance (ANOVA) revealed significant differences among the populations for all investigated traits. The Rabor, Darb-Behesht, Bafat, and Rayen populations exhibited superior biomass and plant height, while the highest EO percentages were recorded in Bardsir (3.03%), Darb-Behesht (3.02%), and Sirjan (2.97%). Pearson correlation analysis indicated a strong positive correlation between EO percentage and leaf dimensions, suggesting the pivotal role of essential oil gland density within the leaf tissue. Cluster analysis categorized the populations into two distinct groups, facilitating the selection of genetically distant parents for breeding programs. Furthermore, path analysis revealed that the fresh weight of flowering shoots exerted the greatest direct effect on dry weight yield, while plant height and the number of branches served as significant auxiliary traits. This study successfully identified superior populations for integration into breeding programs aimed at enhancing both the quantity and quality of Thymus production in the Kerman province.