Growth, yield, chemical composition, and antioxidant activity of essential oils from two thyme species under foliar application of jasmonic acid and water deficit conditions

Jasmonic acid (JA) exerts biological activity in plant responses to environmental stress as well as development. The effect of foliar application of JA and combination with deficit irrigation on some characteristics of two thyme species, including Thymus vulgaris and T. daenensis were investigated. Treatments comprised 0, 200, and 400 µL JA applied to plants under normal, slight drought, and mild drought stress conditions. Irrigation levels had a significant effect on growth traits in terms of herbage dry weight, plant height, number of branches, and leaf area index. Foliar application of JA influenced the essential oil yield and the main components of the oils. Percentages of carvacrol, γ-terpinene, and p-cymene in the oil extracted from the plants under stressed conditions were higher than non-stressed plants, whereas percentage of thymol was significantly reduced under drought stress. In both thyme species, the JA significantly improved carvacrol and thymol contents in the oils, antioxidant activity, plant height, and root length, but reduced the essential oil yield and amount of γ-terpinene in the oils. In conclusion, the foliar application of JA reduced the negative effects of water stress on thymol amount in T. daenensis, and γ-terpinene content in T. vuglaris.