Effect of salicylic acid on growth, yield, and active substances of Citrullus colocynthis L.

Citrullus colocynthis L. is an important medicinal plant belonging to the family Cucurbitaceae. All parts of the plant namely leaf, flower, root, fruit and seed contain active substances valuable for medicinal applications such as diabetes. In this study effect of foliar application of salicylic acid on growth, yield, and quantity of active substances was investigated. Evaluated characteristics included the fresh and dry weight of foliage, plant length, fruit yield, as well as chlorophyll, flavonoid, phenol contents, and antioxidant activities. Various concentrations of salicylic acid (0.3, 0.6, 1.2 mM) along with control (no treatment) were applied. Based upon statistical analysis (p≤0.01) the results showed that salicylic acid had a significant influence on evaluated parameters. The best performance and highest values of investigated parameters were observed in the level of 0.3 mM salicylic acid. In this concentration, the highest fruit yield (11136.1 kg ha^‑1 compared to 6344.4 kg ha^‑1 in control), fresh weight (9972.2 kg ha^‑1 compared to 5152.8 kg ha^‑1 in control), dry weight (2430.6 kg ha^‑1 compared to 1236.1 kg ha^‑1 in control), flavonoids (7.1769 mg 100 g^‑1 FW compared to 4.0433 mg 100 g^‑1 FW in control) were achieved. The highest phenol content (18.113 mg 100 g^‑1 FW compared to 10.723 mg 100 g^‑1 FW in control) was recorded in 0.6 mM salicylic acid and the highest amount of chlorophyll (1.10692 mg 100 g^‑1 FW compared to 0.69353 mg 100 g^‑1 FW in control) observed at the concentration of 1.2 mM salicylic acid. In conclusion, the most effective concentration of salicylic acid in terms of growth, yield, and active substances was obtained in 0.3 mM and can be recommended for the production of this medicinal plant.