Effect of foliar application of salicylic acid and zinc oxide on growth, photosynthetic pigments and antioxidant enzymes in tomato plants

This study was conducted to investigate the growth and physiological responses of tomato (Solanum lycopersicum) plants to long-term foliar application of zinc oxide (ZnO) and salicylic acid (SA) in low concentration. This experiment was carried out under the pot conditions in cocopeat and perlite medium and Hoagland's nutrient solution was used to irrigate tomato seedlings. Tomato seedlings were sprayed with two concentrations (0 and 5 mg/l) zinc oxide and/or two dose (0 and 5 mg/l) of salicylic acid with three-day intervals during two months. Single and combined foliar application of salicylic acid and zinc oxide improved plant growth and fruit fresh weight. The applied treatments increased plant height, shoot fresh weight, root fresh weight, and fruit fresh weight. Individual and combined treatments of salicylic acid and zinc oxide also significantly increased the content of photosynthetic pigments, including chlorophyll a (Chla), Chlb, and carotenoids. A significant increase in the activity of catalase enzyme was recorded due to the foliar spray of zinc oxide and salicylic acid, especially the combined treatment. Peroxidase enzyme activity also showed an increasing trend in response to foliar application of zinc oxide and salicylic acid. Overall, this study provided physiological evidence on how the application of ZnO and salicylic acid in appropriate concentration can improve primary metabolism and antioxidant system. It is obvious that performing further researches, especially at molecular levels, can improve our knowledge in the field.