Evaluation of the responses of basil to the application of salicylic acid and gibberellic acid

Growth regulators are widely used to stimulate the growth of crops and vegetables, increase yield, and improve their quality. The aim of this field experiment was to determine the effect of salicylic and gibberellic acids on the physiological and biochemical leaf traits of flowering (55???60-day-old) sweet basil (Ocimum basilicum L.) after spraying them on the 18th day (growth stage of 3???4 leaves). The relative humidity between June and August was 36???54%, the rainfall 0???23.2 mm, and the maximum and minimum temperatures were 28???35.8??C and 10.6???17.4??C, respectively. In the experiment, salicylic acid at concentrations of 0, 250, 500, and 750 ??M and gibberellic acid at concentrations of 0, 125, 250, and 375 ??M were used. The use of both acids resulted in significant (P ??? 0.05) increases in the plant height, leaf chlorophyll content, leaf relative water content, leaf area, dry weight of aboveground parts of the plants, and the percentage of the essential oil content with a synergistic effect. The strongest effect was observed when salicylic acid at the concentrations of 250 and 500 ??M was sprayed by the combination with gibberellic acid at a concentration of 250 ??M: such treatment resulted in increases in the leaf area index, the chlorophyll content index, the chlorophyll and carotenoids content, relative water content, soluble carbohydrate content, dry weight, essential oil content and essential oil yield (kg ha-1). The higher essential oil yield of 21.7 kg ha-1 (compared to 9.9 kg ha-1 in the control) was due to both the higher mass of the aboveground part 1702 kg ha-1 (compared to 999 kg ha-1 in the control), and the 1.28 times higher content of leaf essential oil. The experimental data shows that spraying sweet basil by the combination of 250 and 500 ??M salicylic and 250 ??M gibberellic acids may increase both the yields of the aboveground part of the plant and of essential oil.