A major resistance gene used to protect winter wheat from yellow rust disease has been overcome by evolving strains of the pathogen, according to findings from the Agriculture and Horticulture Development Board (AHDB) and its research partners.

It follows unusually high levels of yellow rust reported this spring in both Recommended List (RL) variety trials and commercial winter wheat crops. AHDB first issued an early warning in April advising growers not to rely on the current RL disease resistance ratings for yellow rust. The alert enabled farmers to adjust fungicide spray programmes, with the dry spring facilitating timely treatment.

Unusual activity was first seen in late March in an RL fungicide-untreated trial near Sunderland. At this site, several varieties had yellow rust symptoms, despite being classified as resistant to the disease at the young plant stage on the RL (2025/26).

Paul Gosling, AHDB Senior Crop Production Systems Scientist who manages the RL, said: "Following discussions with plant breeders, we suspected that an important yellow rust resistance gene – Yr15 – had potentially been overcome. We subsequently observed similar resistance-breakdown patterns more widely in RL trials, starting in southern Scotland, before spreading down the eastern coast of England, down as far as East Anglia."

Trial operators sent diseased leaf samples from the affected RL trial sites near Sunderland and Berwick-upon-Tweed for analysis by the AHDB-funded UK Cereal Pathogen Virulence Survey (UKCPVS). The NIAB-led service confirmed that Yr15 had failed.

Not only did the pathogen infect test varieties carrying Yr15, but it also sporulated profusely – clear evidence of a resistance breakdown. Molecular markers further confirmed the presence of the Yr15 gene in several of the varieties impacted at the young-plant stage, with this genetic testing funded by NIAB.

The initial tests prioritised testing of varieties with a strong level of adult-plant stage resistance (disease rating 8 or 9), according to RL 2025/26. Hard Group 4 varieties such as KWS Dawsum, LG Typhoon, and Champion were among those found to carry the now-compromised gene.

NIAB is currently testing a wider range of varieties, with further genetic screening also being done by the John Innes Centre in Norwich and the Global Rust Reference Centre in Denmark.

The Yr15 resistance gene, which was discovered in the 1980s, confers broad-spectrum resistance against genetically diverse yellow rust isolates (from a large worldwide collection of more than 3,000) and was an important line of defence.

Paul added: "Adult plant resistance has clearly taken a knock, but the full impact will depend on a myriad of other resistance genes, which vary from variety to variety. Some varieties appear to be fighting back, whereas others are recording unusually high disease levels. Although we have not seen the unusual symptoms towards the South or the West, it appears to be spreading fast. No doubt it will impact on variety choice and disease management across the UK next season."

RL disease ratings are usually calculated from datasets of between three and five years. As there is evidence of a major change to the pathogen population, the dataset will be limited to a single year (harvest 2025) for the disease rating calculations in the next RL edition (2026/27).

AHDB is currently analysing yellow rust data from its UK network of variety trials and will issue revised disease resistance information on the RL web page as soon as possible: https://ahdb.org.uk/rl