A rhizomania strain, which can overcome previously resistant varieties, has spread to sugar beet in Norfolk, Broom’s Barn research has found.

But new genetics in candidate varieties do give better resistance against the more aggressive strain.

The AYPR strain of rhizomania, which is caused by beet necrotic yellow vein virus transmitted by the soil-borne fungus Polymyxa betae, has now been identified in 22 fields, mainly around the Orford/Woodbridge area of Suffolk where it was first found, Mark Stevens, a plant pathologist at Broom’s Barn said.

But it has also been found in Essex, and this year for the first time, on one field along the A11 Thetford/Norwich corridor in Norfolk, he said. “It is not clear why or how it has spread to there, but it could be due to soil movement or machinery.”

In the Orford area, the strain has killed beet plants in the centre of localised epidemics in fields, and decreased yields by up to 40%.

However, tests of new KWS and SES Vanderhave varieties alongside standard resistant varieties show the additional genetic resistance bred into the varieties is giving better resistance to the strain than standard varieties, he said.

Yields from both KWS’s Diana and SES Vanderhave’s Magistal variety in separate trials where the AYPR strain was present gave 40-60% yield increases over commercially available resistant varieties.

In the Elsom trial, which markets SES Vanderhave varieties in the UK, Magistal also maintained sugar levels, with the current resistant varieties sugar dropping by around 1% due to the virus. But higher sugar contents were less clear cut with the KWS variety in trials this season.

Both new varieties combine existing rhizomania “RZ” resistance genes with resistance derived from wild beet species.