Early yellow rust data highlights pathogen diversity

The UK Cereal Pathogen Virulence Survey (UKCPVS) is exploring ways to speed up the release of disease resistance data. Catherine Harries, who manages disease research at AHDB, examines the early release of yellow rust data – this provides further evidence of extreme diversity in the UK population.

UKCPVS has piloted an approach to provide faster information on the resistance status of the UK’s wheat yellow rust (and brown rust) populations.

A new report includes information on the young plant resistance of winter wheat varieties to yellow rust, based on screens of samples received during 2023.

The screens used a variety subset (with selection based on the area grown or those most likely to generate the most valuable resistance data).

It is useful to understand the resistance status at the young plant stage, as varieties react differently compared to the adult plant stage (which starts from about stem extension). Knowing the variety resistance risks across crop growth stages can help inform the development of fungicide programmes.

The pilot screen used 36 samples (isolates) of yellow rust, which were received by UKCPVS between February and July 2023. This is far more than in the standard UKCPVS young plant test (used to help inform young plant resistance classifications in the RL), which is limited to five isolates per year.

This enhanced screening has highlighted tremendous diversity in the UK’s yellow rust population, with common and rare infection responses observed (Figure 1).

For example, three varieties currently classified as resistant in RL 2023/24 (Merit, LG Illuminate and RGT Bairstow) were susceptible to just one isolate collected in Nottinghamshire (23/030), which did not affect other varieties in the subset.

Three further varieties (KWS Extase, Crusoe and KWS Zealum), also currently classified as resistant in RL 2023/24, were susceptible to more than one isolate in this enhanced screen.

The results show the difficulty associated with classifying varieties as resistant (R) or susceptible (S) based on a screen with a small number of isolates. This is why the RL classifications also take into consideration susceptibility seen in RL trials early in the season.

However, varieties that are susceptible to a greater number of isolates are more likely to be prone to problems in the field at the young plant stage and should be the priority for monitoring.

UKCPVS has also confirmed the presence of three new pathotypes, which are associated with unique infection patterns (virulence profiles) on a set of wheat accessions (not current RL varieties). However, this is not unusual, bearing in mind the current diversity in the UK’s yellow rust population. These pathotypes may remain rare curiosities.

Enhanced yellow rust screening results

Figure 1. The number of yellow rust isolates that infected seedlings in a subset of RL varieties. Young plant resistance (R) and susceptibility (S) information and adult plant resistance disease rating (published in RL 2023/24) are indicated

UKCPVS will continue to monitor the population to help identify any significant changes.

The next edition of the RL (2024/25), which will be published online next month (27 November 2023), will include updated resistance information.

AHDB is investigating how to progress the pilot as part of efforts to deliver robust and timely resistance information to growers.

This blog is based on information published in the UKCPVS report: ‘Wheat yellow rust and brown rust: review of the 2022-23 season’.