Breathing space to keep UKs rhizo-free status
WITH truly rhizomania-resistant sugar beet varieties to suit UK conditions still some years away, the proposal to allow growers affected by the disease to shift their contracts to clean farms is a good move.
So says Brooms Barn pathologist Mike Asher. He believes this would give a breathing space allowing the UK to retain its rhizo-free status* until there are varieties good enough to perform properly on infected land. "If we were to lose that status and let things slide, the disease would create problems for many more people," he warns.
Last years experience at Elveden Farms in Norfolk, where 400ha (988 acres) of crop had to be destroyed because of the disease, put pressure on the NFUs compensation scheme and raised doubts about the effectiveness of the current containment policy.
Similar outbreaks this year could make the British Sugar/NFU Rhizomania Stewardship Scheme particularly welcome, says Dr Asher. Under it affected growers could temporarily assign their sugar beet contracts to be grown on unaffected farms.
"My own view is that beet should be taken off farms if we know they are infected." That would reduce the risk of the virus that causes the disease building up in the soil, he explains.
Last year the UKs first partially resistant variety, Ballerina, was grown commercially. "Unfortunately there were a number of outbreaks of rhizomania in it, including those at Eleveden, so it is not the solution in the long term.
"Now we have Rebecca and Rosana, which are marginally better and probably good enough to be grown in low-risk fields on high risk farms and yield well.
"All three reduce the amount of virus build up 100-fold which is a substantial contribution. In a trial where we had 90% root infestation in susceptible varieties, Ballerina had only 20%.
"What we really need are varieties that take that figure down to zero. But getting to 5% would be a big step and one which may be possible with a new resistance gene from wild beet. Combined with the current Holly gene it should provide dual resistance and significant control."
Eventually varieties with a wild beet gene which resists the fungus carrying the virus should offer a much more robust defence for growers, Dr Asher believes. "We are testing some this year alongside NIAB trials to see if virus build up is affected. Thats the acid test."
Depending on the results, the material could be made available to breeders. "They are interested. But it would have to be crossed and back-crossed into their own programmes, so it could be seven to eight years before commercial varieties see the light of day."
• The UKs rhizo-free status is due for renegotiation in November, and the stewardship scheme is only part of the proposals recently put forward to the EC for consideration, notes British Sugars Chris Carter.