Effects of different levels of sulfur and selenium on some morphological and antioxidant properties of onion (Allium cepa L.) cv. Germez Azarshahr

Onion is one of the vegetables greatly consumed in the food chain of people and researchers are always trying to improve itsnutritional quality. This study was conducted to investigate the effect of different levels of sulfur (32, 64 and 128 mg L-1 sulfate) and selenium (0, 1 and 2 mg L-1 selenate) on the growth and antioxidant properties of red onion cv. Azarshahr. The study was performed under hydroponic conditions. Results showed that the concentrations of sulfate and selenate and the interaction of them had a significant effect on the most of growth characteristics of onion plants. The highest fresh weight and diameter of bulb (35.70 g and 38.24 mm) was observed in 128 mg L-1 sulfur in combination with 2 mg L-1 selenate. There was a positive correlation between selenate and sulfate with the bulb fresh weight and diameter of onion. The highest percentage of bulb dry matter content (16%) was obtained in 64 mg L-1 sulfate combined with 1 mg L-1 selenate. At all concentrations of sulfate, the plant height was reduced by increasing of selenate. In addition, selenium accumulation was increased in the onion by increasing selenate concentrations in all levels of sulfate. By increasing selenium, antioxidant activity and phenol and flavonoid contents of bulb tissue was increased.