Multiple tube-like reproductive structures (aecia) of stem rust protruding from Berberis vulgaris. SEM photography by Kim Findlay, John Innes Centre
This information has been adapted from a news release issued by the John Innes Centre.
Wheat stem rust resulted in small disease outbreaks in Western Europe recently. The industry has been advised to work together to develop the knowledge and tools required to keep this crop pathogen at bay.
A single infected wheat plant was also discovered in the UK, at a site in Suffolk, in 2013. Although an isolated case, it is the first known example of the disease in the UK in over 60 years.
Erumpent stem rust pustules can be seen on the stems of a wheat plant found in Suffolk. Photograph courtesy of Paul Fenwick, Limagrain UK Ltd.
Following genetic tests, led by Diane Saunders and Brande Wulff at the John Innes Centre, it was discovered that the UK strain belongs to the Digalu race of the fungus. In 2013, this same strain caused small outbreaks in Sweden, Denmark and Germany, as well as major outbreaks in Ethiopia. Major outbreaks occur in higher-temperature climates, which favour the pathogen.
Although unlikely to be an immediate threat to UK production, predicted changes to the UK climate could make the conditions more conducive to the disease, particularly warmer temperatures.
Life cycle of stem rust. Left-hand images show elongated blister-like lesions caused by stem rust on wheat. Photograph courtesy of Paul Fenwick, Limagrain UK Ltd.
The pathogen has not been a focus of breeding programmes in recent years. In fact, over 80 percent of UK wheat varieties tested are susceptible to this strain, according to results from Jane Thomas at the National Institute of Agricultural Botany. European wheat varieties also lack resistance genes.
The good news is that scientists and plant breeders are now working together on genetic solutions, although such solutions will probably take a considerable amount of time to reach commercial wheat varieties.
As wheat stem rust is closely related to wheat yellow and brown rusts (all Puccinia species), however, fungicides used in the UK, such as azoles, should control the disease, in case the disease returns to our shores. But, as with all disease challenges, genetic control is the ultimate goal.
The role of common barberry in the life cycle of stem rust
Cereal rusts have complicated life cycles, involving five different types of spore and two hosts, wheat and common barberry.
Common barberry was almost removed completely across much of England by the early part of the twentieth century, as part of efforts to reduce the risk of stem rust appearing on crops.
On barberry, unlike on wheat, stem rust completes its sexual cycle and produce a mass of genetically different strains. Fortunately, such spores only travel short distances (less than 20 metres). This differs to the genetically identical spores produced on cereal crops, which can blow on wind for thousands of miles.
In the last few decades, barberry shrubs have been planted to conserve an endangered species – the Barberry Carpet moth – at a handful of sites across the country. Diane Saunders’ group is now working alongside farmers and conservation groups to map and sample barberry across the UK, as part of an effort to understand the shrub’s potential to enhance rust pathogen diversity.