Changes in essential oil-content and composition of ajowan ( Carum copticum L.) seeds in response to growth regulators under water stress

Abstract

Abstract Two separate field experiments were conducted in 2014 and 2015. In 2014 changes in essential oil content and in 2015 changes in essential oil composition of ajowan seeds in response to water tress and growth regulators were investigated. The experiments were arranged as split plot based on RCB design in three replicates, with irrigation treatments in main plots and foliar sprays of water (control), salicylic acid (SA) (0 and 1 mM) and abscisic acid (ABA) (0 and 50 μM) in sub plots. In 2014, seeds were harvested in weekly intervals at six stages. With progressing seed development, seeds per plant, seed weight and seed yield enhanced, leading to an increase in essential oil yield, despite decreasing essential oil percentage and per seed. Essential oil percentage increased, but seed and essence yields decreased as a consequence of water stress in both years. Foliar application of ABA and especially SA enhanced essence yield of ajowan seeds via increasing seed yield and essence content. About 70 compounds were identified in essential oil of ajowan seeds, some of which only induced by the water stress and hormonal treatments. Thymol and γ-terpinene were the major constituents of seed essential oil. The terpineol, trans-carveol and tetrathiapentacene were only induced by water stress. The cyclopropane, trans-decalone-1, isopulegone, hexadecanoic acid, linalool and 1-decanol, 2-hexyl- were specifically synthesized in SA treated plants, and β-phellandrene, 3-fluoro-dl-phenylalanine and 1,5-dimethylbicyclo[3.2.1]octane were only found in ABA treated plants. In general, water stress reduced most of the essential oil components, but foliar spray of SA and ABA enhanced percentages of many constituents and their yield per unit area.