Effects of curing, moisture, leaf removal, and artificial inoculation with soft-rotting bacteria on the incidence of bacterial soft rot of onion (Allium cepa) bulbs in storage

Abstract

Experiments were carried out over two growing seasons to investigate the effects of moisture, leaf removal and artificial inoculation with soft-rotting bacteria at five different stages of foliage-drying on the incidence of bacterial soft rot of onion (Allium cepa) bulbs in storage. All four experimental factors (curing duration, wetting of foliage, foliage removal and inoculation of onions with soft-rotting bacteria) had substantial effects on soft rot incidence. The number of days that bulbs were cured before the foliage wetting, leaf removal and inoculation with soft-rotting bacteria had substantial effects on bulb rotting. Numbers of bulb rots declined as onion foliage became more desiccated, demonstrating that soft-rotting bacteria infect onions more readily though live green leaf tissue than through dead or senescent leaves as commonly accepted. Onion plants whose foliage was intact before being subjected to moist or wet conditions had higher levels of storage rots in their bulbs than plants that had been topped, indicating that in wet conditions, soft-rotting bacteria infect more readily through intact leaf tissue than through neck tissue of topped plants. In topped plants, the percentage decay in bulbs decreased as foliage became more desiccated, largely because wounding to bulbs during topping occurred less frequently in properly cured onions. Modification of husbandry practices and monitoring of weather during harvest and field-curing are recommended as measures to reduce the incidence of bacterial soft rot of onion in storage and transit.