تاکسونومی و بیوسیستماتیک (Sep 2022)
Introducing High-yielding Populations of Native Species of the Genus Thymus in Iran
Abstract
Natural essential oils derived from plants have particular importance in various markets such as agricultural, pharmaceutical, healthcare, cosmetics, and hygiene industries. Thyme has a special significance among the rest of aromatic plants. Thyme essential oil is yellow, brownish, and reddish to brown and is obtained from the distillation of leaves and flowers of Thymus vulgaris, as well as other species of thyme. It has various applications in the healthcare and cosmetic industries. Therefore, searching for different types of thyme to produce essential oils can be appealing to various industries. The results of the comparison of dry matter and essential oil production among 108 populations of 9 species of Iranian thyme and 4 populations of agricultural thyme (T. vulgaris) showed that the native populations of thyme species in Iran have a much higher economic and pharmacological potential than T. vulgaris. For instance, the specific populations of T. kotschyanus and T. daenensis can produce dry matter and essential oils in higher yields. The germplasm to be cultivated and utilized could be chosen purposefully by the designated usage of the product. If the purpose of producing thyme is to obtain dry matter for seasoning or spice, then the population 104 of T. kotschyanus, population 60 of T. fallax, population 91 of T. kotschyanus, and population 107 of T. daenensis could be considered. If, however, the purpose of cultivation of thyme is to extract essential oils, then population 104 of T. kotschyanus, population 60 of T. fallax, population 90 of T. daenensis and population 67 of T. fedtschenkoi could be utilized.Key words: Thyme Crop, Native Thyme, Essential Oil Production, Medicinal Plants, Economic Plants. IntroductionThyme essential oil is a dark yellow or reddish-brown liquid with a strong pleasant smell and a sharp and persistent taste, which is obtained by the distillation of the leaves and flowering branches of Thymus vulgaris L. and other thyme species. It has been shown that 40% of its volume is made up of phenols (thymol and carvacrol) and a small amount of cymene and linalool.Genus Thymus L. has significant species diversity and includes 220 to more than 250 species in the world, scattered in the northern temperate region, from Greenland to Kamchatka, and one of the most important centers of its diversity is in the Mediterranean region and West Asia. Thymus has 18 species in Iran, of which four species (T. persicus, T. marandensis, T. daenensis, T. lancifolius) are endemics.Studying the chemical diversity of different populations, at both interspecies and intraspecies levels, remains one of the important aims of plant phytochemical studies with the purpose of discovering chemical types containing optimal amounts of known compounds or new compounds with medicinal value. Materials and MethodsSeeds of 108 populations of 9 native species of thyme, along with 4 populations of cultivated thyme from different regions of Iran were obtained. In the winter of 2009, the seeds were planted in the greenhouse, and in the following spring, they were transferred to the research farm.Seedlings were planted on the farm, in three replicates with a completely random block design and grew for 3 years under the same agricultural conditions. Then, in the fourth and fifth years, the stems were harvested and dried in the shade at room temperature. The dry weight of the samples was measured with a digital scale. Extraction of essential oils was performed using water and a Clevenger apparatus for three hours.Active ingredients were separated using a gas chromatography device connected to a mass spectrometer (GCMASS). Identification of spectra was calculated with the help of their inhibition indices and with the injection of normal hydrocarbons (C7-C25) under the same conditions and with the injection of essential oils by a computer program in BASIC language. In this study, the amounts of 10 important chemicals, i.e., p-cymene, 1,8-cineol, δ-terpinene, Linalool, Thymol, carvacrol, Borneol, Geraniol, α-Terpineol, Geranylacetate, and α-Terpinyl acetate have been compared. The yield data of dry matter and essential oil obtained from thyme germplasms were compared in a complete random block design over several years by SAS software version 2002. Results and ConclusionThe results of the data analysis showed the average weight of dry matter and essential oil among different germplasms. The production of dry matter of each genotype during two consecutive years is not significantly different. Among the 4 samples of cultivated thyme, accession 37 had the highest production of essential oil and dry matter compared to other samples of cultivated thyme; therefore, native samples were compared with this accession.All 9 native thyme populations had a higher average essential oil production per individual plant than that of the cultivated thyme under the same conditions. The highest amount of essential oil produced belonged to T. kotschyanus. The comparison of the amount of thymol in the active ingredients of the essential oil obtained from the examined thymes showed that the essential oil of the T. migricus had the highest percentage of thymol, which is the highest percentage of thymol reported in the essential oil of any thyme species, to the best of our knowledge.By comparing the above results, it could be said that according to the purpose of using thyme, the germplasm used can be somewhat different. If the purpose of planting and producing thyme is to produce dry matter for use as a seasoning or for such uses, it can be obtained from the population of 104 species of T. kotschyanus, the population of 60 species of T. fallax, the population of 91 species of T. kotschyanus and the population of 107 species of T. daenensis can be used. However, if the purpose of planting thyme is to produce more essential oil, the population of 104 species of T. kotschyanus, the population of 60 species of T. fallax, the population of 90 species of T. daenensis, and the population of 67 species of T. fedtschenkoi can be used. Financial SupportThere is no specific 4financial support for this research to be announced.
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