A major resistance gene used to protect UK winter wheat from yellow rust has been rendered ineffective, scientists have /confirm/ied. The Agriculture and Horticulture Development Board (AHDB) has warned that the pathogen’s evolving strains have overcome the Yr15 gene, a previously critical resistance measure for the agriculture industry.

The Yr15 resistance gene was discovered in the 1980s and confers broad-spectrum resistance against genetically diverse yellow rust isolates. It was an “important line of defense,” notes the AHDB.

The research follows unusually high levels of yellow rust reported by the AHDB this spring in both Recommended List (RL) variety trials and commercial winter wheat crops.

The organization first warned farmers in April, advising them not to rely on the current RL disease resistance ratings for yellow rust. The alert enabled farmers to adjust fungicide spray programs, with the dry spring facilitating timely treatment.

Paul Gosling, AHDB senior crop production systems scientist who manages the RL, says:

“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, wheras others are recording unusually high disease levels. Although we have not seen the unusual symptoms toward 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.”

The team observed similar resistance-breakdown patterns more widely in RL trials, starting in southern Scotland and spreading down the eastern coast of England as far as East Anglia.

Tracking the spread

The researchers first detected the gene breakdown in untreated trial plots in the North East, and it has since spread rapidly down the eastern coast of England. Several popular commercial wheat varieties, including KWS Dawsum, LG Typhoon, and Champion, have shown unexpected levels of infection. 

AHDB and its research partners sent infected wheat leaf samples from test sites near Sunderland and Berwick-upon-Tweed to the UK Cereal Pathogen Virulence Survey for analysis. The National Institute of Agricultural Botany (NIAB)-led team confirmed that the Yr15 resistance gene had failed.

The disease infected wheat varieties with Yr15 and spread heavily, showing an apparent breakdown in resistance. Genetic tests, funded by NIAB, confirmed that the affected young plants did carry the Yr15 gene.

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

Meanwhile, AHDB notes it is analyzing 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.”