Exogenous Application of Foliar Salicylic Acid and Propolis Enhances Antioxidant Defenses and Growth Parameters in Tomato Plants

Salicylic acid (SA) and propolis (PR) are known to regulate the physiological process and to have a relevant role in bioactive compounds content. Our experiment was designed to evaluate the effect of SA and PR application on the growth, yield, and quality parameters of tomato grown for the fresh market in field conditions in Egypt. We studied the effect of twelve treatments where SA (0.50, 1.00, 1.50, 2.00, and 2.50 mM) and PR (1, 2, 10, 20, and 100 mg propolis mL⁻¹) were applied at increasing doses as a sole agent or combined each other (1.50 mM + 10 mg mL⁻¹ for SA and PR, respectively). An untreated control was also considered. Tomato plants treated with SA (0.50, 1.00, and 1.50 mM) showed a significant effect in all traits especially SA1 (0.50 mM) in growth parameters and SA2 (1.00 mM) in pigment and antioxidant content. Propolis foliar application was more effective than SA as it revealed that raising the concentration of aqueous extract enhanced the growth parameters and pigment in tomato. The best result was obtained by the 10 mg mL⁻¹ treatment. The effect of propolis on antioxidant enzymes varied as the 10 mg mL⁻¹ treatment was effective on peroxidases and superoxide dismutase, while 100 mg mL⁻¹ was more effective on catalase. Salicylic acid and propolis have a positive effect on both preserving tomato plants and on nutrient supply, so the mixed intermediate concentration (1.50 mM + 10 mg mL⁻¹) is considered very effective and results in an improvement of all plant traits.