A new race of brown rust identified through the UK Cereal Pathogen Virulence Survey at NIAB TAG last week will have implications for more winter wheat varieties than its highest profile casualty, Stigg.
The next two to three weeks should see more information being made available on other varieties, many of which are highly rated for brown rust resistance at present, says Rosemary Bayles of NIAB TAG.
“It’s an early warning,” she says. “Changes are afoot and the new race won’t be just limited to the one variety that has broken down. There may even be more than one new race.”
Priority has been given to the testing of resistant varieties following the discovery of an isolate that has been able to overcome Stigg’s nine resistance rating in seedling tests, she reports.
“We are now working on finding out which other varieties are at risk. Our intention is to make relevant information available to growers as soon as possible, so they can plan ahead and make the right decisions for the forthcoming cropping year.”
Brown rust came into crops very quickly this year in June and then developed rapidly, which is typical of the disease, she explains.
“Most crops were affected to some extent, but varieties that were previously considered to be resistant have been more susceptible than expected. Samples have been sent into the UK Cereal Pathogen Virulence Survey from a whole range of varieties and regions.”
A huge number of samples have also been received of yellow rust, she adds. “We’re in an earlier stage of processing them than the brown rust samples, but there would appear to be developments with that disease too.”
Further information on the susceptibility of key wheat varieties to yellow rust will also be issued in the next fortnight to three weeks, she says.
Stigg was only added to the 2011/12 HGCA Recommended List last December as a hard milling Group 4 feed variety. Although the variety’s treated yield potential is lower than other feed types, its excellent disease resistance scores were considered to be compensation.
Paul Fenwick of Limagrain, the company which bred Stigg, agrees with Dr Bayles’ findings. “It is a new brown rust race, certainly to the UK, and Stigg is much more susceptible to it than its rating suggests.
“But other varieties in the same trial were also much more susceptible, so it’s highly unlikely it will be limited to just Stigg.”
However, variation within the infected plots makes it difficult to predict what Stigg’s brown rust rating will fall to, he says.
“We will continue to work closely with NIAB. The isolate from that trial is being further investigated and used to test a range of other varieties. But it would appear to be a classic breakdown, featuring major gene resistance.”
He points out that there haven’t been any reported field problems with brown rust on Stigg this year. “It doesn’t cause the same concern among agronomists as yellow rust and there are fungicides that can deal with it.”
Stigg’s other disease-resistance ratings, which include the only eight for septoria on the list, are unaffected, stresses Mr Fenwick.