Evaluation of Quantitative Yield of Two Thyme Species Affected as Different Levels of Drought Stress and the Manure Application

The present study aimed to study the effects of drought stress and manure on some physiological characteristics and quantitative yield of two species of the Thymus, Thymus daenensis Celak and Thymus vulgaris L. For this purpose, a factorial layout based on a randomized complete block design with three replications was done at the Agricultural Research Field of University of Birjand, Iran, during two cropping years 2015 and 2016. Experimental factors included water levels (100, 67, and 33% of field capacity), two species of thyme (T. daenensis Celak and T. vulgaris L.) and manure (Cow manure) (non-application and application of 30 ton/ha). Drought stress reduced plant height, number of lateral branches, number of flowers, relative water content, membrane stability index, and quantitative yield while induced an increase in the amount of ion leakage, proline, phenol, and malondialdehyde compounds. Manure significantly increased the quantitative yield. Further, the amount of ion leakage was lower in the cells of T. daenensis indicating the maintenance of the integrity of cell membranes in the face of water stress, which can result in an enhancement in the efficiency of plant production and, ultimately, an increase in yield crop. In addition, T. daenensis had higher water use efficiency indicating lower vulnerability of this species. Results differentiated two species and T. daenensis can be introduced as superior species in confronting with drought stress.