The UK Cereal Pathogen Virulence Survey confirms that the ‘Warrior-type’ was the dominant yellow rust race in the UK this summer, with no new races detected to date.
The mild 2013 autumn and winter conditions, and continuing favourable weather in 2014, resulted in one of the most severe yellow rust epidemics for many years. At least four different strains of the ‘Warrior-type’ race have been identified so far, all of which were very severe on many of the 2014 HGCA Recommended List varieties.
Fortunately of the 40 varieties on the RL, 20 had an 8 or 9 disease rating for yellow rust, with about 60% of the 2014 UK winter wheat area resistant to the Warrior variants.
NIAB head of pathology Dr Jane Thomas reports that a record number of yellow rust samples were sent to the NIAB-managed UKCPVS disease monitoring service this year. Samples from over 40 different wheat varieties and 15 different counties, ranging from Dorset up to Perthshire, have given the UKCPVS a detailed insight into this year’s disease populations.
“We would like to thank all those growers, agronomists, plant breeders and trials officers who sent in samples. Such a large number will enable us to understand race distribution this year.
NIAB cereal pathologist and UKCPVS manager Dr Sarah Holdgate explains that nearly all the variety samples sent in were from known susceptibles. “UKCPVS yellow rust variety seedling tests are well underway with the first results already available. All of the tests so far have shown that the ‘Warrior-type’ races are completely dominant; it looks as if these variants have gained a strong foothold in the population.
“Very occasionally we may see just one or two stripes on varieties with an 8 or 9 disease rating, which we will test thoroughly over the following season in seedling and field tests, in case they are the early stages of a new race emerging. However, so far there have been no indications of any resistance breakdown this year.”
Dr Holdgate explains that this year’s epidemic has highlighted how damaging the disease can be when a new race comes to dominate the population. The UKCPVS information on race structure feeds into the RL disease ratings, ensuring that the resistance ratings reflect the changing UK population of yellow rust. The ‘Warrior-type’ races are expected to dominate the yellow rust population for next season so 2014/15 variety choice should take this into account.
“Knowing the race structure is very important when planning which varieties to grow around the farm to reduce pressure on spraying. There are many RL varieties which are still resistant to the Warrior races at the adult plant stage, and these can help to make disease management easier. There is still plenty of scope to diversify variety choice, and reduce the area of material susceptible to yellow rust, but check the diversification tables for guidance on how to spread the risk on farm,” emphasised Dr Holdgate.
HGCA’s Dr Jenna Watts adds that the UKCPVS results ensure that any emerging yellow rust races that are starting to become dominant in the UK population are included in the RL inoculated yellow rust trial programme.
“As a result the RL yellow rust disease ratings reflect variety resistance/susceptibility to the current UK populations under high disease pressure situations. Due to the nature of the system RL disease ratings do not contain data from the current season, but these preliminary 2014 UKCPVS results give us further confidence in the current yellow rust ratings.
“However, in the coming season regular monitoring of all varieties, even those with a rating of 8 or 9, is advised as rust populations can rapidly change so that varietal resistance is no longer effective. HGCA has started more in-season disease monitoring activities of untreated RL trials in addition to the assessments done at the end of the season, upon which the disease ratings are based. Monitoring, and the work done by the UKCPVS, is essential to unsure that new rust races are identified at the earliest possible opportunity,” finishes Dr Watts.