The “Warrior” race of yellow rust, first identified in 2011, is now virulent on adult plants of Claire and related varieties, according to the results of the UK Cereal Pathogen Virulence Survey.
Speaking at the presentation of the survey results, Rosemary Bayles of crop consultants NIAB TAG said that the Warrior race is proving to be more complicated than originally thought.
“It was first reported in the UK in 2011, but was also found in France, Germany, Denmark and Sweden in the same year. That’s really quite unusual,” she said.
It has also increased in all of these countries in 2012, with the race accounting for 75% of the isolates tested during 2012 in England, she added.
“There’s something strange about it and the pathogen appears to be identical across all of these countries. The speculation is that it may have originated outside Europe.”
A race of yellow rust named after one of the most popular varieties grown in Denmark, Ambition, is the same as the Warrior race, she revealed.
“The big thing about this race in the UK is that it’s the first time that the Claire resistance has broken down, she reported. “That has implications for varieties such as Alchemy, Beluga and Horatio.”
Otherwise, a yellow rust isolate collected from KWS Sterling in 2011 gave moderate to high levels of infection on adult plants of the variety, she noted.
“But the immediate impact of that race will be small, as there’s a limited amount being grown.”
Varieties which are still resistant to all races of yellow rust include popular choices such as JB Diego, Invicta, Crusoe, Panorama, KWS Gator and Scout, as well as newly recommended Delphi.
Looking at brown rust, Dr Bayles pointed out that changes in races meant that there was greater susceptibility to the disease than there was to yellow rust, with almost three-quarters of the varieties in the ground all coming from diversification group 4.
“That group accounts for over 65% of the current acreage,” she stressed.
An increase in the frequency of virulence for the Stigg group of varieties was recorded, from 16% in 2011 to almost 50% in 2012, while the virulence for Robigus has increased slightly.
“The immediate impact of the Stigg group will be slight, but it should be noted that these resistance sources are being used in breeding programmes.”
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