The effect of foliar application of melatonin and potassium sulfate on the water deficit adjustment and reduction of nitrate accumulation in broccoli

This research was conducted in order to investigate the application of melatonin and potassium sulfate on the quantitative and qualitative characteristics of broccoli (Brassica oleracea var. italica) under water stress. A factorial experiment was performed in a completely randomized design with three replications. The experimental factors included irrigation conditions at two levels (50 and 100% FC), melatonin at three levels (0, 150 and 300 µM) and potassium sulfate at three levels (0, 2 and 5 mM). The results showed that in the treatment of 300 µM melatonin and control irrigation (100% FC), the leaf area was twofold greater than in the treatment of 50% FC without the use of melatonin. The highest activity of the catalase enzyme was observed in the interaction of 50% irrigation level and 150 µM melatonin and the highest amount of malondialdehyde was observed in the same field capacity without the use of melatonin. The highest amounts of chlorophyll a and b were obtained in the interaction of 100% FC, 150 μM melatonin and 5 mM potassium sulfate. The highest amount of head yield was achieved in the interaction of 100% FC with the use of 300 µM melatonin and 5 mM potassium sulfate, and in this treatment, the highest nitrate reductase enzyme activity and the lowest nitrate accumulation in the crop head were observed. The highest content of proline and activity of the peroxidase enzyme were observed under conditions of 50% FC without the use of melatonin and potassium sulfate. The best treatment in most of the interaction traits was melatonin 300 µM, potassium sulfate 5 mM under control irrigation conditions (100% FC). Therefore, the use of these compounds is recommended to improve the physiological characteristics, yield and quality of broccoli.