Unusually high levels of yellow rust in some winter wheat varieties during 2025 have led to a major revision to disease resistance ratings, with significant falls recorded for some widely grown varieties, according to findings from the Agriculture and Horticulture Development Board (AHDB) and its research partners.

The updated Recommended Lists (RL) yellow rust disease resistance ratings have been released earlier than usual to help farmers adapt management strategies for harvest 2026.

Following the unexpected appearance of yellow rust in some varieties in RL trials in early spring, AHDB advised farmers not to rely on the RL 2025/26 yellow rust ratings when setting fungicide programmes.

In May, the NIAB-led UK Cereal Pathogen Virulence Survey (UKCPVS) confirmed initial suspicions that a major yellow rust resistance gene – Yr15 – had been overcome by a new strain of the disease. This gene features in many commercial varieties, with some varieties losing up to five rating points in the RL 2026/27 data release.

How the ratings are calculated

RL adult plant disease resistance ratings use a numerical scale: from 1 (least resistant) to 9 (most resistant). Usually, disease ratings for rusts (yellow and brown) are based on three years of trial data, which since RL 2021/22 has been weighted to give more influence to recent results. This makes them more sensitive to changes in the rust population.

However, due to the sudden emergence of the new Yr15-virulent strain, the RL 2026/27 yellow rust ratings are based solely on harvest 2025 data that best represent the current situation. It follows a rigorous validation process.

AHDB Crop Protection Scientist Siobhan Hillman, who leads on the rating calculations, said: "This is only the second time we have issued the yellow rust ratings based on a single year – the previous occasion was in 2016 following another significant shift in virulence.

"Genotyping analysis by NIAB and the John Innes Centre suggests that the Yr15-breaking strain probably evolved by mutation in late 2024. In the UK, it was first seen in North East England and spread rapidly in spring, impacting many RL trials and commercial crops. Yr15-virulent isolates have also been identified in several other European countries this year."

Impact on varieties

NIAB-funded work indicates that the Yr15 gene may be present in about a third of RL varieties. Twelve varieties have seen ratings drop by two to five points in the RL 2026/27 data release. Some varieties believed to contain Yr15 carry other effective yellow rust resistance genes and have recorded relatively little change in their ratings, while varieties without Yr15 are unaffected. Around half of winter wheat varieties on RL 2025/26 maintain the same rating or fall by only one point – and a few improved due to declines in other yellow rust strains.

Several candidate varieties are also susceptible to the new strain, which could affect their chances of RL inclusion later this year. Others performed relatively well, including some with a yellow rust disease resistance rating of 8.

Young plant resistance

Since RL 2023/24, young plant resistance (r) or susceptibility (s) status has been presented alongside resistance ratings. The status is determined by UKCPVS screens and disease data from RL trials (before stem extension).

On RL 2025/26, 13 out of 38 winter wheat varieties were classified as having resistance at the young plant stage. As this is likely linked to Yr15, most varieties are expected to be classified as susceptible to yellow rust at the young-plant stage in RL 2026/27.

Looking ahead

The 2025 ratings reflect the average performance of varieties from 33 trials (28 naturally infected, 5 inoculated). While the new strain was not present in all trials – especially towards the far south of England – its virulence and the widespread use of Yr15 mean it is likely to spread further in 2026. As it may take a couple of years for the yellow rust population to settle, ratings may be impacted next year, although unlikely at the scale seen this year.

As a result, it is important to monitor all varieties closely, even in traditionally low-risk regions, and to report unexpected rust levels to UKCPVS.

Information on the RL 2026/27 disease ratings and UKCPVS are available at ahdb.org.uk/rl. The new RL 2026/27 edition will be published on 1 December 2025. The UKCPVS stakeholder event 2026 will take place on 12 January in Cambridgeshire.