Red 24 now established in the UK wheat yellow rust population

Red 24 was first known to be present in the UK in 2016 and the group probably played a key role in the unexpected disease levels and revision of disease ratings in that year.

Recent tests on yellow rust isolates present in crops in 2017 reveal Red 24 is now the most dominant group in the UK yellow rust population.

These findings were presented at the annual UK Cereal Pathogen Virulence Survey (UKCPVS) Stakeholder Event, which took place recently in Cambridgeshire reports the AHDB.

Wheat yellow rust

Compared with 2016, yellow rust levels were generally lower in 2017 and disease observations much more in line with the disease ratings presented in the AHDB Recommended Lists.

Dr Sarah Holdgate, UKCPVS project manager based at NIAB, said: “Autumn 2016 was quite dry, and cold snaps last spring seemed to have dampened the disease going into the summer. We’ve also only received two yellow rust samples so far this year, most likely due to the cold weather this winter.”

In total, 114 wheat yellow rust samples were received by UKCPVS in 2017, this compares to 340 samples received in 2016.

Tests on the samples received during 2017 revealed the continued dominance of Red group isolates.

Red 24 isolates were the most commonly found (36 per cent frequency), followed by Red 28 (29 per cent frequency) and Red 11 (14 per cent frequency).

Pink and purple groups were not detected in 2017. Beyond the dominant red group, only blue-group isolates were detected in 2017. This, however, did not include the Blue 7 group which, like Red 24, was one of the causal groups of isolates behind the 2016 epidemic.

Sarah said: “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. For example, Red 24 is relatively damaging compared to other isolates and its continued presence in the UK is not welcome news.”

Several new pathotypes from the already highly diverse Red groups were also identified in 2017 (Red 27 to Red 30), in addition to another pathotype (yet to be assigned to a group).

Red 30 is similar to the PstS14 isolates detected elsewhere in Europe. PstS14 was first detected in Morocco and Sicily in 2016 and caused widespread disease epidemics in Morocco in 2017.

At this stage, the potential impact of this new pathotype on UK wheat varieties is unknown. Adult plant trials have been set up to help quantify the risk.

Wheat brown rust

Brown rust appeared relatively late in the season in 2017, with high levels of the disease observed in crops from June. No unexpected disease, however, was reported to UKCPVS.

Isolates have become more complex in recent years and the latest seedling tests found 26 different pathotypes in the 27 isolates tested.

Barley and wheat powdery mildew

Mildew pressures were relatively high in 2017. For wheat powdery mildew, there was an increase in virulence frequencies for most resistance genes but there were no significant reports of any resistance breakdown in the field. For barley powdery mildew, virulence frequencies were generally stable, although some increased, whereas others decreased. Once again, UKCPVS received no reports of unexpected disease in crops.

A new four-year EU-funded project called ‘Rustwatch’ was also announced at the event. Led by the Global Rust Reference Centre in Denmark, the project will monitor rusts across Europe and develop a coordinated early warning system.

As part of Rustwatch, people are being asked to extend their monitoring and sampling beyond cereal crops to include the alternative host – common barberry.

Progress in research looking to introduce durable yellow rust resistance in wheat crops was also outlined at the event.