Evaluation of Drought Tolerance in Thymus daenensis subsp. daenensis Ecotypes

Thymus daenensis subsp. daenensis is one of the endemic medicinal plants in Iran that is valuable for high essential oil content and high thymol in its essential oil. In order to study the effect of drought stress on some agronomical traits of 12 ecotypes of Thymus daenensis subsp. daenensis from different regions of Iran and their classification, two experiments (under normal and drought stress conditions) were carried out using randomized complete block design with four replications in Payame Noor University of Abarkouh (Yazd province) in 2017-2018. 14 agronomical traits were recorded in drought and non-stress conditions. The results of combined analysis of variance revealed that the differences among ecotypes were significant (p<0.01) in all the studied traits. Drought stress reduced leaf width, plant area and shoot fresh weight 41.4%, 39.5% and 39.4%, respectively, compared to normal condition. The highest genetic diversity was observed for shoot fresh weight under non-stress (40.31%) and drought stress (44.33%) conditions. The highest broad-sense heritability was belonged to shoot dry weight (97.65%), number of days to first (99.1%) and 50% flowering (99.65%) and essential oil content (99.7%). Shoot fresh and dry weight, number of days to first and 50% flowering were the traits related to drought tolerance. Cluster analysis, based on Ward method and by using Eucilidian distance, classified Thymus daenensis subsp. daenensis ecotypes under stress and non-stress conditions into three groups. Drought tolerant ecotypes were placed in second group under both conditions. The results showed that Khoramabad1, Khoramabad2, Arak1 and Fereydunshahr ecotypes are suitable for improvement drought tolerance in Thymus daenensis subsp. daenensis.