Foliar application of salicylic acid improved the yield and quality of the essential oil from Dracocephalum kotschyi Boiss. under water deficit stress.

Salicylic acid (SA) is considered a plant hormone that has an important role in the plants' growth and tolerance to abiotic stress. In addition, proline (PL) as an amino acid plays an important role in regulating cell osmotic pressure in environmental stresses. This investigation was done to study the impacts of the foliar application of SA and PL on the content and chemical compositions of the essential oil from Dracocephalum kotschyi Boiss. (Lamiaceae) under water deficit conditions at the research field, Southwestern Iran during 2017-2019. The experiment was performed as a factorial experimental in a randomized complete block design (RCBD), which irrigation (optimal irrigation and deficit irrigation regime) and the foliar application (control, foliar spraying of SA and PL at 1 mM) were experimental factors. The essential oils were extracted by hydro-distillation and analyzed using GC/MS and GC-FID. The sprayings of PL and SA on the plants improved the essential oil yield. α-Pinene, limonene, neral, geranial, geraniol, geranyl acetate, geranic acid methyl ester, α-campholene aldehyde, and eucalyptol were identified in the essential oil. The impact of water deficit was significant on the essential oil content and the percentages of the major constituents. Generally, the amounts of some components increased under water deficit stress. The foliar application of SA reduced the negative impact of water deficit on the yield and quality of the D. kotschyi essential oil. In conclusion, the foliar spray of SA under water deficit stress is suggested for the higher yield and better quality of the essential oil of D. kotschyi. [ABSTRACT FROM AUTHOR]