Effects of leaf cutting on bulb weight and pungency of short-day onions after lifting the plants

Abstract

Short-day onions (Allium cepa L.) grown in the southern regions of the United States are commonly undercut and then dried for a few days before the bulbs are clipped and harvested. We conducted a study to evaluate the effects of leaf cutting on bulb weight and pungency of short-day onions after plant lifting in ‘TG 1015Y’, ‘Legend’, and ‘Texas Early White’ cultivars. When about 50% of the leaf had collapsed, plants were lifted from the field and the leaf was either cut at the neck (cut) or left intact (uncut, control). The plants were laid out to dry for 0, 3, or 7 days in a greenhouse with natural ventilation and the pungency and weights of the bulbs and leaves (partially dried to approximate normal field curing or dry weight) were measured. In a bulb–leaf paired test, bulb pungency was retained at the initial level in the cut treatment, while it showed an increasing trend in the uncut treatment, resulting in a gain of ˜0.8 μmoles mL−1 after 7 days in ‘TG 1015Y’. However, leaf pungency in the uncut treatment had 2.5 and 4.8 μmoles mL−1 less than that of the cut treatment after 3 and 7 days, respectively. Among cultivars, bulb pungency generally showed that the cut treatment had lower pungency levels, with some variation in change patterns and magnitudes of difference by the cultivar. The mildest cultivar ‘Legend’ had no difference but the most pungent cultivar ‘TEW’ showed 1.0–1.3 μmoles mL−1 less pungency by the cut treatment. Bulb weight was not reduced by the cut treatment, while leaf dry weight was generally heavier in the three cultivars. We considered that the lower bulb pungency in onions from cut plants was attributed to the severance of translocation of flavor compounds from leaf to bulb. Therefore, leaf clipping at the time of lifting and subsequent field curing is beneficial for producing less pungent onions for some cultivars.