Just one spore could push European ash trees to the brink

The research was led by senior author Matthew Clark a Research Leader in plant interactions at the Natural History Museum, focusing on plant pathogen research and developing techniques to tackle biological problems.

The team investigated the fungal spores that cause a disease known as dieback, which threaten 95% of all European ash trees. Dieback has already destroyed more than 80% of young ash trees in Norway and killed or severely damaged a 25% of the species in southern Sweden. The comprehensive genome sequence study at the Earlham Institute, a leading research institute focusing on the development of genomics and computational biology, has revealed that the dieback problem could have been caused by just one or two mushroom-like fruiting bodies of a fungal pathogen called Hymenoscyphus fraxineus. The analysis further suggested that the spores came to Europe from Asia.

The researchers found European fungal samples from the UK, Norway, France, Poland and Austria demonstrated a low genetic diversity, only an eighth of that found in fungus from a single Japanese woodland. The researchers believe that this represents a much larger genetic diversity amongst Asian fungus.

In its native Asia, the fungus is a leaf pathogen and has little impact on its host tree. It is widespread and extremely diverse, but relatively harmless to Asian ash species. However, in Europe it is killing trees at an alarming rate and is replacing native fungus. Should further Asian genetic diversity be accidently bought into Europe, for example by bringing in new fungal isolates, it could potentially increase the severity of the disease in Europe.

Matthew Clark says, “The risk is that if the pathogenic fungus gets the chance to mate and reproduce with just one new individual, the resulting offspring could have the ability to kill the remaining ash trees that have survived the disease so far.”

Dieback was first spotted in Europe in Poland in 1992, where it probably arrived on commercially imported ash from East Asia. It steadily moved west and was found in the UK in 2012, where spores may have landed from the continent.

The disease causes dark brown or orange lesions on leaves, followed by wilting, lesions of dead cells on shoots and then diamond-shaped lesions on the stems. Finally, the crown of the tree dies back and the pathogen either kills the tree or weakens it to such an extent that it succumbs to other pests or pathogens.

Matthew Clark managed a large group of scientist throughout the research including lead author Mark McMullan from the Earlham Institute, who 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.”

The study, ‘The ash dieback invasion of Europe was founded by two individuals from a native population with huge adaptive potential,’ is published in the journal Nature Ecology & Evolution.

Notes for editors

Interview: Matthew Clark is available for interviews

Media contact: Tel: +44 (0) 20 7942 5654/+44 (0) 7799 690151 Email: press@nhm.ac.uk

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• The Earlham Institute (EI) is a world-leading research Institute focusing on the development of genomics and computational biology. EI is based within the Norwich Research Park and is one of eight institutes that receive strategic funding from Biotechnology and Biological Science Research Council (BBSRC) - £5.43m in 2017/18 - as well as support from other research funders. - as well as support from other research funders. EI operates a National Capability to promote the application of genomics and bioinformatics to advance bioscience research and innovation.
  EI offers a state of the art DNA sequencing facility, unique by its operation of multiple complementary technologies for data generation. The Institute is a UK hub for innovative bioinformatics through research, analysis and interpretation of multiple, complex data sets. It hosts one of the largest computing hardware facilities dedicated to life science research in Europe. It is also actively involved in developing novel platforms to provide access to computational tools and processing capacity for multiple academic and industrial users and promoting applications of computational Bioscience. Additionally, the Institute offers a training programme through courses and workshops, and an outreach programme targeting key stakeholders, and wider public audiences through dialogue and science communication activities.

• The research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC), Defra, the Economic and Social Research Council (ESRC), the Forestry Commission, the Natural Environment Research Council (NERC), the Scottish government and the French National Research Agency (ANR).