Evaluation of Growth, Essential Oil Content and Composition in Four Thyme Species under Dryland Farming System in Zagheh, Rangeland, Khoramabad, Iran

In order to study the variation of four thyme species for aerial parts biomass, essential oil content and composition, a study was carried out in Zagheh, Rangeland, Khoramabad, Iran. Seeds of four species of Thymus pubescens Boiss. & Kotschy ex Celak., Thymus daenensis Celak. Thymus daenensis subsp. lancifolius (Celak.) Jalas and Thymus kotschyanus Boiss. & Hohen. were collected from their natural habitat in Lourestan province, Iran. Seeds sown in Jiffy pots in glasshouse in September 2016 and the seedlings were transferred to the field in October 2016 using Randomized Complete Block Design (RCBD) with 3 replications. Each unit of the experiment consists of 40 plants in two rows with 50 cm distance between rows and 50 cm between plants within rows. Data were collected for aerial parts biomass, morphological traits and essential oil percentages over two years 2017-2018. The essential oils of all samples were obtained by hydrodistillation, in flowering stage and the essential oil components were identified using gas chromatography (GC) and gas chromatography/mass spectrometry (GC-MS). Considerable variation was found between species for fresh and dry weight of aerial parts biomass, plant height, root length and essential oil content. The mean values of aerial parts biomass, crown diameter and essential oil in T. daenensis were higher than other species. For the root length, the higher value was obtained in T. pubescens. The lower and higher essential oil content with average values of 1.53% and 1.95% were obtained in T. pubescens and T. daenensis subsp. lancifolius, respectively. The results indicated that the major components in the essential oil were carvacrol (5.8, 18.5, 42.4 and 33.5%) and thymol (78.9, 51.9, 36.19 and 42.7%) for T. daenensis, T. kotschyanus, T. daenensis subsp. lancifolius and T. pubescens, respectively.