The UK Cereal Pathogen Virulence Surveyconfirms that the Warrior-type was the dominant yellow rust race in the UKthis 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 severeyellow rust epidemics for many years. At least four different strains of theWarrior-type race have been identified so far, all of which were very severeon many of the 2014 HGCA Recommended List varieties.
Fortunately of the 40 varieties on the RL, 20had an 8 or 9 disease rating for yellow rust, with about 60% of the 2014 UKwinter wheat area resistant to the Warrior variants.
NIAB head of pathology Dr Jane Thomas reportsthat a record number of yellow rust samples were sent to the NIAB-managedUKCPVS disease monitoring service this year. Samples from over 40 differentwheat varieties and 15 different counties, ranging from Dorset up toPerthshire, have given the UKCPVS a detailed insight into this years diseasepopulations.
We would like to thank all those growers,agronomists, plant breeders and trials officers who sent in samples. Such alarge number will enable us to understand race distribution this year.
NIAB cereal pathologist and UKCPVS manager DrSarah Holdgate explains that nearly all the variety samples sent in were fromknown susceptibles. UKCPVS yellow rust variety seedling tests are wellunderway with the first results already available. All of the tests so far haveshown that the Warrior-type races are completely dominant; it looks as ifthese variants have gained a strong foothold in the population.
Very occasionally we may see just one or twostripes on varieties with an 8 or 9 disease rating, which we will testthoroughly over the following season in seedling and field tests, in case theyare the early stages of a new race emerging. However, so far there have been noindications of any resistance breakdown this year.
Dr Holdgate explains that this yearsepidemic has highlighted how damaging the disease can be when a new race comesto dominate the population. The UKCPVS information on race structure feedsinto the RL disease ratings, ensuring that the resistance ratings reflect thechanging UK population of yellow rust. The Warrior-type races are expected todominate the yellow rust population for next season so 2014/15 variety choiceshould take this into account.
Knowing the race structure is very importantwhen planning which varieties to grow around the farm to reduce pressure onspraying. There are many RL varieties which are still resistant to the Warriorraces at the adult plant stage, and these can help to make disease managementeasier. There is still plenty of scope to diversify variety choice, and reducethe area of material susceptible to yellow rust, but check the diversificationtables for guidance on how to spread the risk on farm, emphasised Dr Holdgate.
HGCAs Dr Jenna Watts adds that the UKCPVSresults ensure that any emerging yellow rust races that are starting to becomedominant in the UK population are included in the RL inoculated yellow rusttrial programme.
As a result the RL yellow rust diseaseratings reflect variety resistance/susceptibility to the current UK populationsunder high disease pressure situations. Due to the nature of the system RLdisease ratings do not contain data from the current season, but thesepreliminary 2014 UKCPVS results give us further confidence in the currentyellow rust ratings.
However, in the coming season regularmonitoring of all varieties, even those with a rating of 8 or 9, is advised asrust populations can rapidly change so that varietal resistance is no longereffective. HGCA has started more in-season disease monitoring activities ofuntreated RL trials in addition to the assessments done at the end of theseason, upon which the disease ratings are based. Monitoring, and the work doneby the UKCPVS, is essential to unsure that new rust races are identified at theearliest possible opportunity, finishes Dr Watts.