Ash dieback "could get even worse" if new spores introduced

Europe's ash dieback epidemic may have been caused by just one or two fruiting bodies of the fungal pathogen Hymenoscyphus fraxineus, suggesting even resistant trees are at threat from further spores arriving from its native East Asia, according to extensive new genetic research.

Image: Björn S (CC BY-SA 2.0)
Image: Björn S (CC BY-SA 2.0)

A team of over 30 researchers, from The Earlham Institute, The John Innes Centre, Fera Science, The Sainsbury Laboratory, Kew Gardens, The Natural History Museum, The Universty of Edinburgh as well as from insitutes in France, Norway and Japan, found that diversity of the fungus found across Europe is just an eighth of that found in a single Japanese woodland, so is likely to be a just a tiny fraction of that found across Asia.

Allowing some of that Asian genetic diversity into Europe, for example by bringing in new fungal isolates, has the potential to increase the severity of the disease in Europe, they warn.

Lead author, Earlham Institute population genomicist Mark McMullan, said: "It’s incredible that from such limited genetic diversity the ash dieback fungus has already devastated trees across Europe.

"Now that the disease is established, the introduction of genes from outside of Europe would tremendously increase the genetic diversity of the pathogen and seriously threaten the remaining ash trees."

Senior author and Natural History Museum research leader Matthew Clark added: "The risk is that if the pathogenic fungus gets the chance to mate and reproduce with just one more individual, the resulting offspring could have the ability to kill the remaining ash trees that have survived the disease so far."

The disease was first observed in Europe in Poland in 1992, where it was thought to have arrived on commercially imported ash from east Asia. It was first discovered in England in 2012, where spores may have landed from the continent.

Co-author John Innes Centre crop genetics specialist Dr Elizabeth Orton said: "Tree populations take so long to recover from attacks by invasive pathogens that it is vital to restrict the movement of potentially infected plants into and around Europe in accordance with the ‘precautionary principle’."

National legislation currently prohibits the movement of ash trees both into and around the UK.

Breeding work has already begun in the UK and Denmark to select parent stock for trees that will be more resistant to ash dieback.

The research is published in Nature Ecology & Evolution.

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