The Effect of Nitrogenous Fertilizers on Antimicrobial Activity and some Physiological Characteristics of Onion (Allium cepa L.)

Onion is a medicinal plant which have many uses in traditional medicine. It is a valuable crop since ancient times and it ranks second after tomato among cultivated vegetables in the world. Also, onion has great importance in the diet of Iranian people. In this study effect of different nitrogen levels (56, 112, 168 and 224 mg.L-1) on antimicrobial activity and some physiological characteristics of bulb extracts were studied.The highest and lowest amounts of inhibitory efficacy of methanol extract of onion bulbs at concentration of 0.30 mg.L-1 against Pseudomonas aeruginosa and Bacillus subtilis, were observed. According to the results, different levels of nitrogen had a positive effect on the antimicrobial properties onion bulb extract. With increased nitrogen concentration in nutrient solution, antimicrobial activity onion bulb extracts increased. With the increase in nitrogen concentration in nutrient solution content antioxidant activity, total phenol, total flavonoids, and ascorbic acid were increased. Increasing the concentration of antioxidant compounds was associated with increased antimicrobial activity of onion bulb extract. In recent years, the consumption of onion has increased due to its flavor and health benefits. The beneficial properties of onion are mainly related to its high content of sulfur compounds and flavonoids, and the role of these compounds as antioxidants, anti-microbial and anti-cancer have been proven. Nitrogen was effective on the inhibitory effect of bulb methanol extract, which could be due to the effect of nitrogen on the metabolism of sulfur compounds and flavonoids in bulb.