University of Tehran International Journal of Horticultural Science and Technology 2322-1461 5 1 2018 06 01 Identification of Drought Tolerant and Sensitive Species of Thyme through Some Physiological Criteria 53 63 67764 10.22059/ijhst.2018.255144.231 EN Mohsen Ashrafi Department of Agronomy and Plant Breeding, Faculty of Agriculture, University of Zanjan, Zanjan, Iran. Mohammad Reza Azimi Moqadam Department of Agronomy and Plant Breeding, Faculty of Agriculture, University of Zanjan, Zanjan, Iran. 0000-0003-4767-8241 Parviz Moradi Research Division of Natural Resources, Zanjan Agricultural and Natural Resources Research and Education Centre, AREEO, Zanjan, Iran. Farid Shekari Department of Agronomy and Plant Breeding, Faculty of Agriculture, University of Zanjan, Zanjan, Iran. Ehsan MohseniFard Department of Agronomy and Plant Breeding, Faculty of Agriculture, University of Zanjan, Zanjan, Iran. Journal Article 2018 03 31 Drought as the most important abiotic stress has deleterious effects on plants. Developing drought tolerant varieties can help produce plants in a sustainable way. This study was conducted to identify drought tolerant and drought sensitive thyme species including <em>Thymus vulgaris</em>, <em>T. vulgaris</em> (origin: Spain), <em>T. carmanicus</em>, <em>T. daenensis</em> and <em>T. kotschyanus</em> and to study the mechanism used by them to cope with drought stress. For this purpose, relative water content, water use efficiency, soil water depilation rate, root:shoot ratio, drought resistance index and a new criterion "FC ceased growth" were used. <em>T. carmanicus</em> and <em>T. daenensis</em> had the lowest and the highest reduction on relative water content, respectively. In terms of water use efficiency and soil water depletion curve, the highest and the lowest values were detected for <em>T. daenensis</em> and <em>T. carmanicus</em>, respectively. The most and the least root:shoot ratios were recorded for <em>T. daenensis</em> and <em>T. vulgaris</em> (origin: Spain), respectively. Analyses by drought resistance index and PCA revealed that <em>T. carmanicus</em> is drought susceptible, <em>T. kotschyanus</em> and <em>T. vulgaris</em> are semi-drought susceptible, and <em>T. daenensis</em> and <em>T. vulgaris</em> (origin: Spain) are semi-drought tolerant species. FC ceased growth analysis showed that <em>T. carmanicus</em> stopped its growth at higher FC, while <em>T. kotschyanus</em> stopped it at lower FC. Therefore, based on this criterion and considering the sustainability of growth under drought condition, <em>T. carmanicus</em> and <em>T. kotschyanus</em> are the least and the most drought tolerant <em>Thymus</em> species. https://ijhst.ut.ac.ir/article_67764_291601c53aba7bb60954f1841e083edb.pdf