Genetic resistance brings hope for ash trees
In 2012, a deadly new fungal disease targeting the ash tree arrived in Britain. Since then, ash dieback has killed millions of trees. Professor Richard Buggs and his team discovered genetic variation that makes some ash trees resistant to the disease. Thus, selective breeding can mitigate the disease’s impact.
The genetic markers identified by Buggs have been included in the design of a new custom genotyping array produced by Thermo Fisher Scientific, helping to fight the disease in the UK and across Europe by effectively screening for these resistance markers.
A vital tree in our ecosystem
Ash (Fraxinus excelsior) is the UK’s third most common native woodland, hedgerow and urban tree species. There are an estimated 100 million ash trees in Britain.
Ash is used in the timber industry, as fuel and for flood management, and, of course, helps to remove carbon dioxide from the atmosphere. Ash trees provide food and shelter to more than 900 species. But since 2012, the fungus Hymenoscyphus fraxineus has afflicted ash populations, causing enormous numbers of trees to die. The UK Government Department for Environment, Food and Rural Affairs (Defra) have made fighting this epidemic a priority.
A draft genome
In April 2013, Buggs and PhD student Elizabeth Sollars published the first draft ash genome online, funded by a NERC Urgency Grant. An improved genome assembly and analyses were later published by Buggs, Sollars, Kelly, Cooper and collaborators at the Earlham Institute, Earth Trust, and Universities of York and Exeter in Nature in early 2016.
In 2017, with direct funding from Defra, Buggs, Kelly and PhD students Jonathan Stocks and Carey Metheringham were able to identify 3,149 genetic loci in the ash genome which were associated with resistance to the fungus. With this information (published in Nature, Ecology and Evolution), they were able to show how selective breeding would develop trees that were resistant to ash dieback disease.
A viable long-term solution
It was clear that a breeding programme for increased resistance would offer a long-term strategy to ease the effects of the epidemic in Europe. Using the genetic information that Buggs and his team identified could accelerate this programme.
In 2019/20, Buggs collaborated with researchers at Wageningen University (The Netherlands) and INRA (France) in the EU Horizon 2020 project “B4EST”, Adaptive BREEDING for productive, sustainable and resilient FORESTs under climate change.
Together, these researchers were able to design a genotyping array that helps tree breeders throughout Europe to propagate trees resistant to ash dieback.
A more hopeful prognosis
Working with collaborators at Kent County Council, the John Innes Centre, the Faculty of Forestry and Wood Technology and Mendel University, Buggs’ team have worked to predict the impact of ash dieback.
When the disease was first identified in 2012, scientists expected more than 95% of trees would die. By analysing mortality rates across Europe, Buggs and his collaborators were able to show that mortality was lower – the highest rates being 85% in plantations and 69% in woodlands. These new guidelines will help to develop a more targeted approach to ash protection.
The work conducted by Professor Buggs has been central to Defra’s ability to manage and respond to ash dieback, helping us make policy decisions about the future of ash trees in the UK that are informed by world-class evidence.— Professor Nicola Spence, Chief Plant Health Officer, Defra, UK Government
A positive media reaction
Buggs’ research has featured in national and international media, including The Times, BBC News, BBC World Service, Financial Times, Economist, Daily Mail, Daily Express, Sunday Telegraph, Guardian, and El Mundo.
Informing UK and Irish Government policy on ash
Buggs’ research led to Defra’s move to breed trees for ash dieback resistance. This policy is seen as a long-term solution to the epidemic.
Buggs’ research underpins key sections in the 2019 Defra Ash tree research strategy. The policy has led to the UK’s first archive of trees tolerant to ash dieback, opened in January 2020.
In December 2020, Ireland’s Council for Forest Research and Development recommended ash breeding in a report that cited Buggs’ work.
Informing the management of existing ash populations
Buggs’ research has directly informed tree management guidelines published by a range of UK public bodies, government departments and conservation charities, including Natural England, the Forestry Commission, The Arboricultural Association, and The Tree Council.
Specifically Buggs’ research has provided more accurate estimates on ash mortality, which has encouraged managers not to pre-emptively fell their ash trees. His evidence shows that resistance to ash is heritable and will respond well to natural selection. This means forestry managers can promote natural evolution by retaining healthy ash trees and promoting natural regeneration.
Making genotyping commercially available
The array that Buggs and colleagues developed has become a commercial product – the Applied BiosystemsTM AxiomTM custom genotyping array for ash, which has helped the European Ash breeding community to accelerate their breeding programmes. The array is being used by tree breeders across Europe. It is used specifically in Europe’s largest ash breeding programme, based on 30,000 trees, in Austria.
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