The Red 24 group of yellow rust isolates is now established in the UK disease population, the UK Cereal Pathogen Virulence Survey (UKCPVS) has confirmed.
Red 24 was first identified in the UK in 2016 and probably played a key role in the unexpected disease levels and revision of yellow rust ratings in that year, which saw the resistance ratings for some Group 3 and 4 winter wheat varieties fall by up to four points.
Tests on yellow rust present in wheat crops in 2017 have revealed Red 24 is now the most dominant group in the UK yellow rust population. The Blue 7 yellow rust group, one of the causal groups behind the 2016 disease epidemic, was absent in 2017 and work is underway to establish whether Blue 7 has been outcompeted by Red 24 or if these variants are being found as part of mixed infections.
Red 24 is relatively damaging compared to other yellow rust variants, says NIAB-based UKCPVS project manager Dr Sarah Holdgate: “Work is underway to establish if Red 24 isolates are outcompeting other isolates. It’s important to understand the make-up of the yellow rust population to understand the impact on varieties. Red 24 is relatively damaging compared to other isolates and its continued presence in the UK is not welcome news.”
Last year was overall much quieter in terms of disease in wheat than 2016, with only moderate yellow rust pressure, adds Dr Holdgate. Brown rust pressure was high but late with disease seen from early June onwards and mildew levels were surprisingly high, thought to be due to favourable weather conditions.
The United Kingdom Cereal Pathogen Virulence Survey is funded by AHDB and Defra (via the Animal & Plant Health Agency) and is managed by NIAB.
Each year the UKCPVS calls on the industry to monitor all commercial wheat and barley varieties and to send in infected leaf samples.