31 July 1998

CSL identifies virus causing widespread early carrot disease

CENTRAL Science Laboratory work has diagnosed the mystery virus afflicting early carrots (Arable, July 17) as parsnip yellow fleck virus.

Plant samples were provided by Watton Produce and the ADAS Plant Clinic at Wolverhampton.

Crops from East Anglia to Scotland have been struck by the disease. Early symptoms are dying off of the younger leaves and distortion and viral mottling of older leaves. Typically 25-35% of plants in affected crops are showing symptoms and as the disease progresses the whole plant dies, says CSL virologist Daphne Wright.

The virus itself does not appear to affect the tap root, but the invasion of secondary fungi may be responsible for the staining and rubbery root tissue reported in some of the diseased crops, she notes.

Also known as viral dieback, parsnip yellow fleck virus is spread from cowparsley in late May and June by the aphid Cavariella aegopodii, or willow-carrot aphid. Luckily, carrot-to-carrot transmission does not happen, as the crop is not susceptible to a second "helper" virus, anthriscus yellows, which is necessary for the disease transmission.

A potyvirus, originally thought to be responsible for the disease, has also been found, but only in a couple of the samples.

"Its presence may enhance disease expression, but the main cause of the severe symptoms seen is thought to be the parsnip yellow fleck virus," says Ms Wright. &#42

The Central Science Laboratory has identified parsnip yellow fleck virus as the mystery disease afflicting early carrots this season. Pic: Courtesy CSL.