Evaluation of growth characteristics and essential oil composition in Nepeta assurgens Hausskn. & Bornm. and N. eremokosmos Rech.

Two species of Nepeta assurgens Hausskn. & Bornm. and N. eremokosmos Rech., are endemic medicinal plants to Iran. This study was conducted to investigate the vegetative traits, aerial parts yield, the quantity and quality of essential oil, as well as evaluating the relationships between these traits in mentioned species under field conditions in Isfahan. The experiment was carried out in a randomized complete block design with three replications over 2017 and 2018. Results showed that the fresh and dry weight of aerial parts in N. assurgens (11353 and 2351 kg ha-1, respectively) was remarkably higher than that of N. eremokosmos (2638 and 527 kg ha-1, respectively). The average content and yield of essential oil in N. assurgens and N. eremokosmos was 1.60 and 0.64%, and 20.16 and 2.21 kg ha-1, respectively. Based on qualitative analysis of essential oil, the total amount of nepetalactone isomers (4aα, 7α, 7aα-nepetalactone, 4aα, 7α, 7aβ-nepetalactone, 4aα, 7β, 7aα-nepetalactone) in N. assurgens and N. eremokosmos was 78.6 and 62.8% on average, respectively. Correlation analysis showed that leaf dry weight, total fresh and dry weight, and large diameter of the plant had the highest correlation with essential oil yield. Stepwise regression analysis indicated that essential oil yield changes were mainly explained by leaf dry weight, essential oil content, total fresh weight, the number of stems and the amount of plant crown cover. In general, according to the results, the superiority of the N. assurgens species was significant and could be recommended as a valuable and high potential yielding plant for pharmaceutical purposes.