Path Analysis Of The Characters Influencing Essential Oil In Three Thymus Species

Thyme is one of the most important medicinal plants which is highly variable within and between species of Thyme are scattered all around the country so that at least one of the species exist in the most part of the country. Ten populations of three Thymus species, called Thymus kotschyanus, T. pubscense and T. persicus were collected from ten different climatic locations and planted in a randomised complete block design. Several morphological characters were recorded on the populations. Essential oil was extracted from the populations and their components were separated and recognized. When a significant difference was detected between the species for the studied characters, path analysis was performed on the phenotypic correlations between the characters and essential oil. There were remarkable interrelationships between the morphological characters and essential oil and its major components. Analysis of the correlation between the essential oil as the independent character and the rest of the characters as the dependent characters revealed remarkable indirect effects of the characters. Number of stomata and leaf length showed the most direct effects on essence increment. On the other hand these characters caused reduction in the essence by indirect effects through other characters. So that the total leaf length effects was negligible (0.222) and number of stomata total effect was negative (-0.498). This phenomenon was also observed for several other characters such as number of protective trichomes and the number of stems. In the other words, leaf length decreased the essential oil through the number of stomata. Number of protective trichomes also decreased the essential oil level through leaf length (indirect effect = -2.034). Chromosome total length direct effect on essential oil is negative (-0.494) but this trait has a highly increasing effect on the essential oil through leaf length (2.602). This effect is decreased by negative indirect effects of the rest of the characters.