26 September 1997

Rhizo outbreak threatens UK beet crop…

Rhizomania-resistant sugar beet grown for the first time in the UK on infected land is performing well, pointing to a brighter future for growers with fields hit by the disease. Robert Harris discovers why

RAMPANT rhizomania has struck a sugar beet crop in Suffolk. Large diseased patches of typically stunted plants with familiar bearded roots are easy to spot.

"This is certainly some of the most severe disease I have seen anywhere in the world," says Mike Asher of IACR-Brooms Barn.

However, a closer look shows only half the crop is affected. Green, healthy plants stand alongside sickly neighbours. And the presence of the disease is not causing the flurry of activity normally associated with a new outbreak of the quarantine-status disease.

That is because rhizomania has been encouraged to develop by late drilling and plentiful irrigation. The crop is part of a Sugar Beet Research and Education Fund trial to assess how well resistant varieties grow on infected soils in the UK.

The disease first struck the site at Upton Suffolk Farms, Herringswell, Suffolk in 1994. Until then, farm manager John Bartlett grew about 162ha (400 acres) of beet on light, sandy soils. That year, ministry checks picked up infection in one field. Further tests showed eight more contained the virus.

"We basically had to stop growing beet, and found other land to maintain our quota," says Mr Bartlett. "It was not worth risking further infections."

The 2.4ha (6-acre) site marks the return of the crop to the farm. Ballerina, a rhizo-resistant variety from German breeder KWS, and Roberta, a susceptible variety from the same stable, have been planted in alternate 12-row strips across the field.

The trial, duplicated on another site at Woodbridge, Suffolk, is a UK first. Until now, Dutch work was the main source of crop performance on infected sites.

As resistant varieties come closer to the market, there is a need to identify how they perform on infected soils in this country, says Dr Asher.

Indications suggest Ballerina will perform at least as well as continental findings suggest, he adds. "On severely infected areas the odd plant is showing symptoms. But in general, the variety is doing very well compared with Roberta strips."

Where disease pressure is less severe, Ballerina shows no rhizomania symptoms. "This is where it is really going to show its worth." Tall plants with bearded roots are easy to find in Roberta, and even seemingly uninfected plants are likely to contain less sugar and higher impurities, he adds.

Roberta yields could be cut by 20-30% in such cases according to collaborative trials carried out by NIAB and the Institute of Sugar Beet Research in Holland, says NIABs Simon Kerr. "But resistant varieties can still produce 8-9t/ha of sugar." However, on clean land, he expects Ballerina to produce about 5% less yield than conventional types, as shown by eight years of NIAB UK trials.

New variety Rebecca, also from KWS, is more promising, he adds. Currently in its second year of official trials, it is the highest yielding variety on non-infected soils.

Rhizomania-resistant Ballerina is producing healthy roots on infected soils at Upton Suffolk Farms, says Mike Asher (left). Farm manager John Bartlett will grow 10ha of the variety next year on clean land.

RHIZORELIEF

&#8226 Resistant variety Ballerina doing well on infected land.

&#8226 Can be grown on clean land on infected farms next year.

&#8226 Probable 5% yield penalty, but reduces disease spread.

&#8226 Wider use of new high yield resistant types possible.