Nutritive Constituents of Onion Grown from Sets as Affected by Water Supply

Abstract

A 3-year experiment was conducted in central Hungary comparing the effect of an irrigation treatment on content and yield of dry matter, storage carbohydrates, vitamin C, total flavonols, and total polyphenols of onion (Allium cepa L.) grown from sets. Rain-fed plots were set as controls. Conditions during the first 40 days of the growing season had a decisive effect on yield and bulb size; warmer and dryer weather during this period resulted in lower yield. Colder and wetter weather conditions resulted in higher bulb yield, but also decreased accumulation of secondary metabolites. Dry matter content values ranged between 12% and 14% and were not influenced by the water supply. Storage carbohydrate-to-dry matter ratio was not changed by the water supply. Total flavonol contents (sum of the concentrations of nine individual flavonols) varied between 430 and 753 mg·kg−1 on a fresh weight basis. Total polyphenol values ranged between 607 and 1029 mg·kg−1 on a fresh weight basis. A statistically significant correlation was found between flavonol content and polyphenol content for the rain-fed treatment, but this was not the case for the irrigation treatment. Irrigation significantly increased total flavonol and total polyphenol concentrations during the dry years. Irrigation significantly increased the bulb yield by 33% to 160%, depending on the year. Consequently, by applying irrigation, yields of nutritive compounds became 1.5 to two times higher.