Effect of Salicylic Acid on Growth and Biochemical Characteristics and Essential Oil Percentage of Lemon Verbena at Different Irrigation Water Salinity

In order to study the effect of salicylic acid on some growth and biochemical characteristics of lemon verbena (Lippia citrodora L.) under salt stress, a pot experiment was conducted as factorial, based on completely randomized design, with four levels of water salinity (control, 50, 100, and 150 mM NaCl) and four levels of salicylic acid (SA) (0, 150, 300 and 450 mg/L, equivalent to 0, 1.06, 2.12, and 3.2 mM, respectively). The results showed that interaction effects of salinity and salicylic acid on all of the studied traits were significant, except leaf dry weight, and fresh and dry weights of root. Based on the results, the highest amount of leaf fresh weight, fresh and dry weights of aerial parts, chlorophyll a and chlorophyll b and carotenoid contents were found in the treatment without salinity and application of 3.2 mM SA. The highest amount of soluble carbohydrate was in the treatment without salinity and application of 2.12 mM SA, the highest proline was in 100 mM NaCl and application of 3.2 mM SA, and the highest total phenol was in 100 mM salinity and application of 2.12 mM SA. Therefore, application of SA (especially at 3.2 mM) under salinity stress (100 and 150 mM NaCl) mitigated the negative effects of this stress, increased morphological traits and photosynthetic pigments, and, conversely, decreased the amount of total phenol, soluble carbohydrates, and proline by reducing salinity stress.   Keywords: Photosynthetic pigments, Plant growth regulator, Proline, Soluble carbohydrates