Forgotten stem rust harboured in barberry

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Stem rust of wheat and barley has throughout history been associated with crop failure and famine, and has recently re-emerged in Western Europe 60 years after the last confirmed case.

Scientists Dr Diane Saunders and Dr Brande Wulff from the John Innes Centre identified the infected plant as carrying a UK strain of the Digalu race of the fungus. Digalu was responsible for a devastating outbreak of stem rust in Ethiopia in 2013, and smaller outbreaks in Sweden, Denmark, and Germany in the same year.

Multiple rust aecia on barberry
Multiple rust aecia on barberry

Further investigations carried out by Dr Jane Thomas at NIAB found that over 80% of UK wheat varieties tested are susceptible to this pathogen. This suggests that if the strain became established in the UK, a large proportion of UK wheat could be at risk.

Paul Fenwick, cereal pathologist at Limagrain UK Ltd and co-author of the study, said: “The discovery of stem rust in Suffolk has so far been an isolated one-off occurrence in 2013; however, with global temperatures set to rise by another 1 or 2 degrees over the next century, stem rust could extend its geographic range.

“There is potential for stem rust to become an increasing threat across Europe.”

The situation is made more complex due to the increasing popularity of the hedge row shrub Barberry, which is an alternative host for several rust pathogens including wheat stem rust.

Over the last twenty years or so Barberry shrubs have been planted in efforts to conserve the Barberry Carpet moth, an endangered species. 

In the current study, the authors identified cereal rust on Barberry in the UK for the first time in decades. Cereal rusts have very complicated life cycles, involving five different types of spore and two hosts that they live on in different stages of their life cycle. On cereal crops, stem rust undergoes asexual reproduction, using the plant’s own resources to produce millions of genetically identical spores. The type of spores it generates on cereals can travel on the wind thousands of kilometres.

Barberry bush stem rust
Barberry bush is an alternative host for rust

However, when Barberry is next to a cereal field the pathogen uses it as an alternate host to complete its sexual cycle, potentially leading to a swath of new genetic strains. Fortunately, the spores that form on Barberry only travel short distances, likely up to 10-20 meters, so for a Barberry bush to spread rust to a cereal field, they must be in close proximity.

Mark Parsons of Butterfly Conservation said “We are very concerned about the potential risk from the possible re-establishment of stem rust. The Barberry Carpet moth is an endangered species restricted to just a handful of sites in this country, it being reliant on Common Barberry for survival.

“We are, therefore, pleased to be working closely with the John Innes Centre both to minimize the potential risk from cereal rust, but also to enhance the populations of the Barberry Carpet, and therefore increase its chances of survival in this country.”

The study: “Potential for re-emergence of wheat stem rust in the United Kingdom” was published in “Communications Biology”

The full report: http://dx.doi.org/10.1038/s42003-018-0013-y

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