Genetic breakthrough offers hope for Scotland’s ash trees ravaged by deadly disease

Researchers from the Royal Botanic Gardens, Kew, Forest Research and partner organisations have produced the first pangenome of European ash, a genetic reference that captures DNA variation across multiple trees rather than relying on a single specimen.

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The study, published in Nature Communications, identified 211 genes potentially associated with resistance to ash dieback, for which there is no immediate cure, including 16 genes found only in some individual trees.

The findings could help researchers identify naturally tolerant ash trees and use their genetic characteristics to develop future generations of the tree with greater resistance to the disease.

For Scotland, where the disease is now widespread, the research comes as the country faces the prospect of losing a substantial proportion of its mature ash.

Forestry and Land Scotland (FLS), the Scottish Government agency responsible for managing national forests and land, estimates that between 50 and 75 per cent of Scotland’s 11 million mature ash trees could die over the next two decades.

FLS said the disease is now so widespread that efforts are increasingly focused on managing safety risks from weakened trees and encouraging naturally resistant ash to regenerate.

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The disease, caused by the fungus Hymenoscyphus fraxineus, was first detected in the UK in 2012.

The fungus damages trees when spores land on leaves and then penetrate the inner structures of the plant, disrupting the woody tissues, including cells that transport water and nutrients. Repeated yearly infections lead to eventual tree death in most cases.

In Scotland it has since become a major threat to a native tree that is particularly valuable to wildlife.

NatureScot, Scotland’s nature agency, said ashwoods are among the richest woodland habitats for wildlife in the country as they support a range of lichens, mosses and invertebrates, while birds including redstarts and wood warblers use ash woodland habitat.

Yet in the new research, scientists believe the trees that survive could hold the key to the species’ future.

The new pangenome revealed more than 3,400 “dispensable” genes — sections of DNA found in some trees but not others. While these genes account for only about 9 per cent of the total, researchers believe some may influence traits such as disease resistance or the ability to cope with environmental stress.

Dr Daniel Wood, a Kew research fellow and the study’s lead author, said the research showed that ash trees contain far more genetic variation than can be seen by examining a single genome.

He said the new resource could also be used to investigate resistance to other threats, including the emerald ash borer, an invasive beetle whose range is advancing across Europe.

Head of Tree Health at Scottish Forestry James Nott said: “This research is a really positive step forward for efforts to breed disease-tolerant ash trees.

“It delivers the first European ash pangenome, revealing previously hidden genetic diversity and identifying candidate genes linked to ash dieback resistance.

“Ash trees in Scotland and across the UK are under threat from ash dieback, as well as other pests and diseases not currently present here.

“The research strengthens understanding of the genetic mechanisms underpinning natural resistance and provides a foundation for future ash recovery efforts. The resource also has value beyond ash dieback, supporting studies of adaptation to climate change, drought tolerance and potential future threats such as emerald ash borer.”