|Perkins Veazie, Penelope|
Submitted to: Subtropical Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/1997
Publication Date: N/A
Interpretive Summary: Sweet onions yields are reduced by feeding damage from the thrips insect or from leaf damage by the purple blotch fungus. The effects of these pests alone or in combination on onion quality and storage life are unknown. In this study, Texas Grano 1015Y onion bulb size was reduce when plants were not field-treated for control of purple blotch or thrips. Bulbs from these etreatments had more weight loss and pungency than those where pests were controlled. These results show that sweet onion quality can be adversely affected by insect and disease pressure.
Technical Abstract: Preharvest infection by Alternaria porri (Ellis), causal agent of purple blotch, or infestation by thrips (Thrips tabaci L.) can greatly reduce yields of short-day onion (Allium cepa cv. 'Texas Grano 1015Y'), but their effects on postharvest quality are unknown. In this study, onions were treated during the production season for control of thrips and purple blotch (treated), control of thrips but not purple blotch, control of purple blotch but not thrips, or not controlled for thrips or purple blotch (untreated). Plants from treatments not having controlled thrips or purple blotch or both had reduced bulb yields compared to control (treated) plants. Bulb size was reduced in onions not treated for purple blotch and thrips compared to other treatments. Harvested onions stored at 13#C for 4 weeks were evaluated for quality and chemical composition before and after storage. Onion sweetness declined during storage for all sizes and was generally lower in bulbs from treatments with high purple blotch or from thrips + purple blotch treatments. Pungency was initially higher in medium sized onions. Pungency increased during storage, particularly in large and extra-large onions, but was not different among treatments. Results indicate that onions subjected to a high incidence of both purple blotch and thrips in the field are of poorer quality at harvest and that quality is further reduced following storage compared to noninfected onions.