14 May 1999

Yield-sapping disease found in Wilts wheat

By Andrew Blake

A DISEASE which can slash wheat output by half has been found in the UK for the first time.

Extensive patches of plants affected by soil-borne wheat mosaic virus appeared in four fields last month on an unidentified farm in Wiltshire, says Christine Henry of the Central Science Laboratory.

The symptoms are a light green or yellowish streaky mosaic pattern, especially on the youngest leaves. Individual plants are stunted.

The disease, like barley yellow mosaic virus and mild mosaic virus, is spread by the fungus Polymyxa graminis. "It has been known since 1978 in France where it has caused a lot of problems and can cut yields dramatically," says Ms Henry. But until April it was unknown in the UK.

"It tends to appear a bit later than BaYMV and BaMMV when the crop starts to regrow after winter." It is at its most aggressive at temperatures of 12-15C (54-59F), she explains. "Wet weather helps the fungal vector. But if the virus doesnt get into the plant during its window of opportunity the crop tends to grow away from it.

"There is no cure and you cannot get rid of it." Once in the soil the fungus can persist for at least 15-20 years to spread the virus to new wheat sowings.

The main defence is to grow resistant varieties, says Ms Henry. "Some French varieties, such as Tremie and Ami are resistant. The UK varieties Charger and Cadenza have shown field resistance in French trials. Soissons has only slight resistance."

Other measures include basic hygiene to prevent contaminated soil being moved from infected land, she explains.

The most likely origin of the Wilts infection is not known, but it could be through soil imported on machinery or perhaps seed potatoes. Birds are only a remote possibility.

"With it so widespread in France and Italy we have been expecting it for some while," says Ms Henry. MAFF has been funding diagnostic work and there is a proposal to use HGCA levy cash to screen UK varieties for resistance on sites known to be infected abroad, she adds.

"The good thing about the present outbreak is that it is on a farm that is fairly well enclosed and self contained. So there is a chance that we might contain it."

Soil-borne wheat mosaic

* First UK find in Wilts.

* Can cut yields by 50%.

* Widespread in France & Italy.

* Resistant varieties defence.

SOIL-BORNE WHEATMOSAIC

&#8226 First UK find in Wilts.

&#8226 Can cut yields by 50%.

&#8226 Widespread in France & Italy.

&#8226 Resistant varieties defence.

Patchy poser… wheat mosaic virus, seen here in Italy, has now been found in the UK. Caused by a soil-borne virus it could lead to big yield losses unless contained, says CSL. The two central leaves in the potted plant from Wilts (left) show the typical mosaic pattern. But there may be a range of symptoms (above).