Accelerated storage losses in onion subjected to water deficit during bulb filling

Abstract

Withholding irrigation during last stages of onion crops is a common practice to minimize losses in storage due to rots. However, it is unclear whether extended periods of water deprivation may affect bulb postharvest behaviour. In this study we analyze the effects of water deficit during the crop cycle on bulb weight loss and sprouting during storage. Two experiments were conducted: one in a glasshouse with two onion cultivars subjected to three treatments of water availability (100%, 80% and 60% of field capacity); the other in the field, with one of these cultivars, subjected to two water availability treatments (dryland and irrigated twice during bulb filling). In both experiments five destructive samplings were done along crop development to assess plant height, number of green leaves, bulb and neck diameter, and whole-plant dry weight. Bulbs were harvested when 50% or more of the tops fell over. Harvested bulbs were classified by weight and then kept in a ventilated chamber at a mean temperature of 15 °C and weighted every two weeks, up to six months. Water deficit led to a significant reduction of bulb size, an acceleration of sprouting and an increased rate of weight loss during storage in both cultivars and under both experimental conditions. Hence, restricted irrigation during extended periods may have negative effects on the conservation of stored onion bulbs which suggests the need to finely adjust water management in this crop.