Effects of NPK complete fertilizer, botamisol, and humic acid on morphophysiological characteristics and essential oil in three Thymus species under drought stress conditions

Due to the valuable role of thyme in the pharmaceutical and food industries of Iran, an experiment was conducted to study the effects of NPK complete fertilizers, butamisol, and humic acid on the morphophysiological characteristics and essential oil of three species of Thymus kotschyanus Boiss, T. vulgaris L., and T. daenensis Celark under drought stress conditions. This research was performed in three separate factorial experiments as a randomized complete block design with four replications in Islamic Azad University, Branch of Shahrekord in the 2021-2022 crop year. Foliar application was done twice with an interval of three weeks after the 10-leaf stage of the plant. Twenty-four experimental treatments included the non-use (A1) and use (A2) of NPK, non-use (B1) and use (B2) of humic acid, non-use (C1) and use (C2) of botamisol under drought stress conditions at three levels of field capacity (D1), 50% (D2), and 75% (D3) loss of gravitational water. The highest amounts of plant height (44.5±1.1 cm), number of main branches (26.4±1.5), plant dry weight (40.5±0.99 g.m-2), total chlorophyll (1.55±0.1 mg.g-1 fresh weight (FW)), and essential oil content (1.88±0.03%) were obtained in the A2B2C2D1 treatment in T. kotschyanus. The A2B2C2D3 treatment resulted in the highest proline content (13.9±0.2 µg.g-1 FW) and lowest essential oil content (0.79±0.1 %) in T. daenensis. Thymol and carvacrol in T. kotschyanus, thymol, ɣ-terpinene, p-cymene, and linalool in T. vulgaris, and thymol, carvacrol, p-cymene, β-caryophylene, α-pinene, and myrcene in T. daenensis were identified as the major essential oil compounds. More nutrient utilization and stress in the least possible along with the temperate climate of the study area led to the introduction of T. kotschyanus as an indicator species in this field.