Large falls in winter wheat yellow rust disease resistance confirmed, as new ratings issued early

Unusual levels of yellow rust in some winter wheat varieties during 2025 have led to a major revision to disease resistance ratings, with large falls recorded for some widely grown varieties.

The Recommended Lists (RL) yellow rust disease resistance ratings have been published earlier than usual to facilitate the adaptation of 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.

This resistance gene played an important role in many commercial varieties, with some losing as many as five rating points in the RL 2026/27 data release.

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 data from three trial years. Since RL 2021/22, the data has been weighted to give more recent data a greater influence on the ratings. This makes them more sensitive to changes in the rust population.

Because of the sudden widespread emergence of the new yellow rust strain with virulence (ability to cause disease) on Yr15, the RL 2026/27 yellow rust ratings have been limited to harvest 2025 data that best represent the current situation. It follows a rigorous validation process.

Siobhan Hillman, who leads on the rating calculations at AHDB, 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, which was also after a 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 the spring, impacting many RL trials and commercial crops. Yr15-virulent isolates have also been identified in several other European countries this year.”

Niab-funded work suggests that the Yr15 gene may be in about a third of RL varieties.

A dozen varieties have seen ratings fall by two to five points in the RL 2026/27 data release. Some other varieties believed to contain the Yr15 gene carry other effective yellow rust resistance genes and have recorded relatively little change in their ratings. Varieties that do not carry Yr15 are unaffected directly by this new virulence. As a result, about half of the winter wheat varieties on RL 2025/26 have the same disease resistance rating or a fall limited to one rating point. Some varieties even recorded a small rating increase, due declines in the yellow rust strains that they are susceptible to.

Several candidate varieties are susceptible to this new yellow rust strain, which will impact their chances of being recommended for inclusion on the winter wheat list later this year. However, some performed relatively well, including some with a yellow rust disease resistance rating of 8.

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, 13/38 winter wheat varieties were classified as having resistance at the young plant stage. As this resistance is highly likely to be associated with Yr15, virtually all varieties are expected to be classified as susceptible to yellow rust at the young-plant stage in RL 2026/27.

The ratings reflect the average performance of varieties (across 28 naturally infected and five inoculated trials in 2025). Although the new strain was not seen in all trials, especially towards the far south of England, given its virulence and the widespread use of the Yr15 gene, it is likely to continue to spread 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, including in regions where yellow rust pressure is not usually high, and to report unexpected levels of rusts to the UKCPVS.

The new RL 2026/27 edition will be available on the RL home page from 1 December 2025.

The UKCPVS stakeholder event 2026 will take place on 12 January in Cambridgeshire.

An example of UKCPVS disease-screening results in 2025 on winter wheat varieties with specific resistance genes. Left to right: known susceptible (Yr3), known resistant (Yr5) and previously resistant (Yr15).