Influence of Salicylic Acid and Citric Acid on the Growth, Biochemical Characteristics and Essential Oil Content of Thyme (Thymus vulgaris L.)

This study was conducted to determine the effect of foliar salicylic acid (SA) and citric acid (CA) applications on growth, biochemical characteristics and essential oil content of thyme (Thymus vulgaris L.) grown under field conditions. Salicylic acid (0.5 and 1 mM) and citric acid (5 and 10 mM) were applied three times during the vegetation at 15 day intervals. Results revealed that foliar application of SA and CA significantly enhanced the vegetative characters i.e. fresh and dry weight of thyme as well as pigments (chlorophyll a and carotenoids) content and essential oil production (1.3 fold as compared to control). There was a positive correlation between fresh and dry weights, chlorophyll a and essential oil. Citric acid treatment especially at 10 mM decreased malondialdehyde (MDA) content. According to our results, applications SA at rate of 0.5-1 or CA at 5 mM should be recommended in order to improve yield and essential oil production in thyme.