Effect of Curing and Storage Conditions On Postharvest Quality of Vidalia Sweet Onions

Vidalia onions are very susceptible to storage disorder botrytis neck rot (BNR) caused by fungal pathogen Botrytis alli. Postharvest storage methods are important to control the incidence of BNR. Controlled atmosphere (CA) storage and curing before storage can reduce the risk of BNR. Curing can be performed either in field or artificially using forced-air heat curing (~37°C). In other crops, such as grape and litchi, postharvest fumigation with sulfur dioxide (SO₂) is used effectively to control botrytis while ozone (O₃) is used as a water and surface sterilant. However little is known about the use of these fumigants in storage of Vidalia onion. The objective of this study was to evaluate the abilities of these storage conditions to control the postharvest botrytis incidence on three Vidalia onion varieties: ‘WI-129’, ‘Sapelo Sweet’, and ‘Caramelo’. All varieties were undercut, then either harvested immediately (zero cure), field cured (2 days), or forced-air heat cured (3 days at 37°C). Bulbs were then sorted and stored in regular air storage (0 to 1°C, 70% R.H.), SO₂ (2500 ppm; one time fumigation), O₃ (1 ppm; continuous exposure), or CA (3% O₂, 5% CO₂).  After 2 and 4 months, bulbs were removed from storage, and evaluated after 1 and 14 days for quality and incidence of disorders. In general, for all cultivars, BNR incidence was greater after 4 months of storage, and after 14 days at room temperature.  There were numerous significant interactions between the curing and storage factors.  However, heat curing was significantly better at reducing postharvest incidence of BNR than either field or zero curing.  Of all the storage treatments, SO₂ resulted in the lowest incidence rate of BNR after both 1 and 14 days of simulated shelf-life periods.  Results suggest that thorough curing is important for reducing the incidence of BNR, while treatments such as SO₂ have potential for significantly reducing post-storage losses due to BNR.