29 September 2000

Soil-borne virus threat set to hit wheat crops

By Charles Abel

CEREAL growers are being urged to remain vigilant for an aggressive new soil-borne virus that can halve crop yields. Two new outbreaks were identified in Kent this summer and growers can expect more, say scientists.

Soil-borne wheat virus was first identified in the UK in April 1999 on five fields near Trowbridge, Wilts. Trials there showed 40% yield loss in infected patches. That is similar to the effects seen in France, where the disease is endemic on well over one-fifth of the wheat area, forcing growers to use resistant varieties only.

Although surveys last year and this spring found no further UK outbreaks, suspicious crop samples sent to CSL by an independent crop consultant in July confirmed two new outbreaks 10 miles apart on the south coast of Kent.

"After first seeing the disease in Wiltshire, these new findings are of even greater agricultural importance," says CSL York-based WSBMV expert Dr Gerard Clover. Further outbreaks can be expected, he warns. "Look at the way Barley Yellow Mosaic Virus took off."

The disease is carried by a soil organism similar to the rhizomania vector. Once land is infected, it is virtually impossible to eradicate the disease, says Dr Clover.

The good news is that HGCA-funded trials on infected land in France have revealed huge differences in varietal susceptibility. Yields ranged from 2.24t/ha (0.9t/acre) for susceptible Equinox to 8.88t/ha (3.4t/acre) for resistant Charger (see table).

The new sites in Kent both showed characteristic plant stunting in neatly defined patches measuring 10-15m across. There is no obvious link between the two farms or the original outbreak site in Wilts, says Dr Clover.

At the Wilts site, a further three fields were confirmed as infected this year, one suffering 60-80% infection and another a 1ha block, suggesting that the virus had been building up for as long as 10 years, says Dr Clover.

He urges all growers to remain vigilant for the disease. "It is notifiable, so if a case is suspected, it should be reported. CSL currently offers free diagnostic testing and can provide detailed advice on how best to cope with the problem."

But the best control of the disease is to avoid it in the first place, says CSL pathologist Dr Neil Giltrap. "Although we have resistant varieties, that resistance could break down. Growers need to think more carefully about the soil that comes onto their farms."

MAFF policy

Current policy is to impose hygiene measures only. "The important thing is to stop the spread to other farms," says Dr Giltrap. "But that must be balanced with not putting excessive restrictions on affected growers. The NFU supports the position. Although it is an extra burden, it is in the best interests of growers not to spread the disease."

Varietal response to WSBMV


Variety Yield (t/ha) % of ave

Charger 8.88 156

Claire 8.34 147

Hereward 8.19 144

Aardvark 7.43 124

Malacca 5.82 102

Buster 5.38 95

Shamrock 5.35 94

Savannah 5.33 94

Napier 4.95 87

Rialto 4.93 87

Consort 4.83 85

Reaper 4.71 83

Riband 4.54 80

Madrigal 4.28 75

Equinox 2.24 39

Ave yield 5.68

NB. HGCA-funded trials in France.