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Tighter plant controls are vital in fight against ash dieback, says report by John Innes Centre scientists in Norwich

Dr Elizabeth Orton of the John Innes Centre inspects young ash trees affected by the ash dieback fungus at Lower Wood, Ashwellthorpe, Norfolk. Picture: Oliver Heaton.

Dr Elizabeth Orton of the John Innes Centre inspects young ash trees affected by the ash dieback fungus at Lower Wood, Ashwellthorpe, Norfolk. Picture: Oliver Heaton.

� Oliver Heaton

Norwich scientists have offered some hope in the battle against ash dieback - but warned tighter controls on plant movements are vital to limit the effects of the deadly tree disease.

A striking contrast between two ash trees beside a bridleway in Broadland, one showing few symptoms of dieback (left) while its neighbour has almost been killed by the disease. Picture: James Brown. A striking contrast between two ash trees beside a bridleway in Broadland, one showing few symptoms of dieback (left) while its neighbour has almost been killed by the disease. Picture: James Brown.

Norfolk became the epicentre of an outbreak in September 2012 when the UK’s first confirmed case of the fungal infection was found in wild trees at Lower Wood in Ashwellthorpe, near Wymondham.

The county’s scientific community was at the forefront of the fightback against the disease, and now researchers at the John Innes Centre, based at the Norwich Research Park, have released a new a study on the Hymenoscyphus fraxineus fungus which causes ash dieback.

Around 5pc of British ash trees appear to be resistant to the fungus, and the findings offer some hope for the future of domestic ash tree populations.

But Prof James Brown from the John Innes Centre, one of the authors of the paper published in the journal Plant Pathology, said it was crucial to prevent any more introductions of variants of the fungus from its native East Asia.

Fruiting bodies of the ash dieback fungus on leaf-stalks in Lower Wood, Ashwellthorpe, Norfolk. Each fruiting body, approximately 2mm across, can release tens of thousands of spores which are dispersed by the wind. Picture: Elizabeth Orton. Fruiting bodies of the ash dieback fungus on leaf-stalks in Lower Wood, Ashwellthorpe, Norfolk. Each fruiting body, approximately 2mm across, can release tens of thousands of spores which are dispersed by the wind. Picture: Elizabeth Orton.

“What this study shows is that once the ash dieback fungus arrived in Europe, it spread to Britain both by wind-borne spores and by trade in plants,” he said. “Other alien diseases could spread in the same way. Because of this, disease control must operate on a European scale. Above all, we should prevent diseased plants getting into Europe.”

The study says the genetic diversity found in all European populations of the fungus is a positive sign for the future of ash, because it allows natural selection to operate, so the pathogen is expected to gradually evolve to adapt to the tree rather than killing it.

“What we expect in the long run is that the ash and the fungi will reach equilibrium – a kind of armed stand-off, and the fungus will merge into the background as a parasite of only moderate importance,” said Prof Brown.

But the study warns that this prospect is based upon the present make-up of the population in Britain and continental Europe. The danger is that new arrivals from East Asia of more genetically diverse strains of the pathogen could be disastrous for European ash.

“It’s strongly suspected that ash dieback disease was imported by timber movements from East Asia. Transport of plant material between countries carries a real risk of spreading disease,” said Prof Brown.

Dr Elizabeth Orton, a post-doctoral scientist at the John Innes Centre and lead author on the paper, recommends the creation of nurseries containing trees with diverse resistance to the ash dieback pathogen, which would allow the trees to breed together to produce seed that can be distributed to bolster resistance throughout the UK.

To read the full report, click here.

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