Early release of wheat rust resistance ratings

AHDB has issued the Recommended Lists (RL) 2020/21 winter wheat disease ratings for yellow rust and brown rust ahead of the release of the full RL.

The early release of the ratings follows reports of higher than expected disease levels in some commercial varieties during the 2018/19 growing season.

In response, RL yellow rust and brown rust trial data were subject to additional checks. This found varietal resistance to these diseases was, generally, in line with recent years. As a result, the revised ratings feature no major changes for most varieties.

RL trials cover a wide range of agronomic and climatic conditions. However, RL disease ratings reflect an average UK situation. Yellow and brown rust populations are highly diverse and dynamic, with different races potentially present across fields and, in some cases, plant to plant.

Unexpectedly high levels of disease on some varieties in 2018/19 could reflect the emergence of a new race(s) at a local scale. The RL is unable to capture such changes. However, even resistant varieties (i.e. disease rating of 8 or 9) can be infected under very high disease pressure.

A clearer picture of whether there has been a shift in the UK yellow and brown rust populations will be available when the UK Cereal Pathogen Virulence Survey (UKCPVS) completes analysis of samples sent in during the 2018/19 season.

Paul Gosling, who manages the RL programme at AHDB, said: “There is a tremendous appetite for information on rust population changes and how they affect disease ratings. This is why we released the ratings early. However, our independent analysis revealed no significant nationwide shift in susceptibility to either yellow or brown rust during 2019.

“Reports of unexpected levels of disease at some locations are a concern, though. Ratings for some varieties have fallen and close monitoring of these varieties is required. However, the dynamic nature of wheat rust populations means vigilance is required for all varieties.”

If higher than expected rust levels (i.e. higher than the varietal disease rating would suggest) are seen, an infected leaf sample should be sent to the UKCPVS for testing: ahdb.org.uk/ukcpvs

Disease resistance ratings (2020/21)

Disease resistance ratings use a simple scale: from 1 (least resistant) to 9 (most resistant). Changes to the 2020/21 winter wheat disease ratings, which can be accessed via ahdb.org.uk/rl, are as follows:

• Yellow rust – three varieties down by one point
• Brown rust – two up by one point, one down by one point and one down by two points
• Several candidate varieties demonstrate good levels of resistance to rusts

The latest information from the UKCPVS, including seedling-stage resistance to yellow rust, is published at: ahdb.org.uk/ukcpvs