Effect of Salicylic Acid on Morpho-physiological Characteristics of Lemon verbena (Lippia citriodora) in In Vitro and Field Conditions

Salicylic acid (SA) is a natural phenolic and a hormone like compound, and its different concentrations and treatment duration cause many actions and reactions in plants. Thus, two experiments were conducted to evaluate the effect of salicylic acid on morphological and physiological characteristics of lemon verbena as an ornamental and medicinal plant in in vitro and field conditions at Miyaneh, Iran. In tissue culture conditions, five concentrations of SA including 0, 2.5, 5, 10 and 20 μM were added to MS culture medium and their effects on lemon verbena growth indices were evaluated. Increasing SA concentrations caused increment in chlorotic leaf number but decrement in normal plantlet percentage and lateral shoots number in lemon verbena explants. However, in low concentrations of SA, longest shoot length, leaf number and chlorophyll content were increased. Although all concentrations of SA improved shoot fresh weight in lemon verbena explants. Under field condition, the effect of salicylic acid at 2.5, 5, 10 and 20 μM concentrations, non spray and spray with distilled water, were evaluated on morphological and physiological traits of lemon verbena. Salicylic acid affected significantly leaf width, inflorescence number, fresh inflorescence and leaf weights and the longest inflorescence length. The negative effect of SA application on leaf width and number and fresh weight of inflorescence was observed. But leaf fresh weight and inflorescence length improved especially in low SA concentrations. Therefore, application of low SA concentrations, because of their enhancing potential effect on vegetative growth of lemon verbena both in field and tissue culture conditions can be recommended.