Wheat variety Theodore has been placed on the AHDB’s first brown rust watch list, with growers advised to remain vigilant for the disease and treat with rust-active fungicides where disease pressure merits it.

Based on trial data, the Recommended List (RL) ratings reveal what has happened in recent seasons, not what will happen.

See also: Why grain maize is key break crop in arable farmer’s rotation

To help bring a more predictive element to wheat growing, the AHDB released the first yellow rust watch list in 2021.

This year sees the first brown rust watch list, and it highlights Theodore, bred by DSV UK.

It is one of two varieties with a brown rust resistance score of 8 (on a scale from 1 to 9, where 9 shows the most resistance), only bettered by Skyfall with its 9 rating.

Catherine Harries, AHDB senior crop protection scientist, said the list aimed to highlight any varieties that appear to be “misbehaving” in RL trials.  

The Group 4 wheat stood out at an RL trial site in Devon with a relatively high level of brown rust (18.8%). At this site, only Crusoe, with a brown rust rating of 3, had more disease (25%).

Interestingly, the UK Cereal Pathogen Virulence Survey (UKCPVS) received a brown rust sample from Theodore just down the coast (Dorset).

“The sampler noted infection levels of 3%, in addition to relatively high disease levels (up to 10%) in some patches. This is much higher than would be expected for a variety with a disease rating of 8,” said the AHDB.

UKCPVS growth room screening tests, conducted in 2022, suggest that the Dorset isolate may be able to unlock a specific resistance gene.

DSV UK wheat breeder Matt Kerton said after monitoring DSV brown rust nurseries across the country, the company has noticed a clear pattern emerging, with some breeding lines susceptible to a Crusoe race of brown rust and others to a Stigg race.

He added that the Crusoe race was much more prevalent, but researchers were starting to see more of the Stigg race occurring, and Theodore appeared to be susceptible to this rarer race.

“We believe Theodore remains a sound choice for growers looking for excellent yellow rust and septoria resistance, but urge them to be vigilant about the new races of brown rust being seen in some parts of the country, and not miss later fungicide applications.”