Effect of Foliar Applications of Salicylic Acid and Chitosan on the Essential Oil of Thymbra spicata L. under Different Soil Moisture Conditions

Abstract

Thymbra spicata L. (Mediterranean thyme) belonging to the family Lamiaceae, is an important medicinal and aromatic plant. The effects of the foliar applications including control and salicylic acid (2.5 and 5.0 mM) and chitosan (0.5 and 1.0 g/L) under different soil moisture condition on the chemical compositions and yield of essential oil from T. spicata L. were investigated. The essential oil from the aerial parts of the herb was analyzed by GC-FID and GC/MS. The foliar spraying of salicylic acid and chitosan significantly improved essential oil yield (2.5-2.7 mL/100 g dry matter) from 30 % to 60 % compared with control (1.7 mL/100 g). In this study, five major compounds including carvacrol, as the predominant constituent of the essential oil (48.40-79.1 %), γ-terpinene (7.27-25.62 %), limonene (3.62-10.35 %), p-cymene (1.69-6.44 %) and β-caryophyllene (1-1.5 %) were identified in the T. spicata L. essential oil. The carvacrol contents in the essential oil increased in the plants spraying by salicylic acid and chitosan compared with control. The effects of foliar application ×soil moisture conditions significantly affected the essential oil; the highest percentage of carvacrol was obtained from salicylic acid (at 5.0 mM) × deficit water stress. In conclusion, the foliar applications of salicylic acid and chitosan could decrease the harmful effects of water deficit on the essential oil yield and the carvacrol concentration in the T. spicata essential oil.