Technique raises hopes of ash dieback tolerance

Selective breeding can now be used to produce strains of ash trees that are tolerant of ash dieback and could potentially restock the national population, according to the research consortium that has studied the genetic basis for such tolerance.

Betty: Edwards (left) and Downie at ash tree in Norfolk
Betty: Edwards (left) and Downie at ash tree in Norfolk

University of York chair of plant genomics Professor Ian Bancroft explained: "We used genetic material from two Danish trees of known susceptibility, from which we identified three markers that are predictive of the degree of susceptibility to, or tolerance of, Chalara. It's not very precise but it is valid. We will now develop a strategy to at least identify which trees are likely to be susceptible and from that promote diverse ash populations that are likely to be tolerant of dieback."

The Nornex open consortium of nine UK and two Scandinavian research bodies was formed soon after the disease was first detected in 2012, to gain understanding of ash dieback at a molecular level. It has since received nearly £1.5m from Defra. Nornex co-ordinator and John Innes Centre (JIC) emeritus fellow Professor Allan Downie said: "We've been able to bring UK strengths in genomics and genetics to this that we didn't have in the past. But there are still questions such as how good the markers are in practice - that will take time because you can't speed up plant growth."

University of East Anglia Genomics Analysis Centre group leader Dr Matthew Clark said: "We want to sequence other UK ash trees to give us more information on how variable our population is and how it differs from the continental population." Bancroft added: "We have a distinctive genetic stock in the UK with a larger proportion of tolerance-associated markers. You don't want a million clones of one tolerant tree."

One promising sign is an apparently tolerant ash tree - that has been named "Betty" - in an undisclosed Norfolk wood near JIC. Norfolk Wildlife Trust senior reserves officer Steve Collin said: "Most ash have it here. The hope is Betty will repopulate the wood. Those trees will have a range of tolerances depending on the partner, though ash can also pollinate itself."

Downie said: "I would be pleased if we only lost 50 per cent of ash trees - we can regenerate from that. But we don't yet know what the final figure is likely to be. They naturally grow for 200 years. Might they live shorter lives? We need 50 trees like Betty, of diverse background. But will tolerant male and female parent trees yield tolerant offspring? Again, we don't know the percentage."

His colleague, JIC researcher Dr Anne Edwards, who was the first to identify the disease in the UK, said: "We have seen a number of trees die quite rapidly at the site, but there is a spectrum of tolerance - some will take longer to die. We think we are through the worst."

Asked by HW about the possibilities of future certified commercial production of replacement stock, chief plant health officer Professor Nicola Spence said: "I would like to see production stimulated of home-grown, biosecure, certified, healthy, tolerant trees, leading to more of them in the landscape. But we are still a long way off that.

"Given that losses would still be quite high, perhaps above commercially viable levels, this would be a possible citizen science project that would generate natural trees, even though you wouldn't get 100 per cent. We also need a broad biodiversity for different soils and environments."

Downie added: "We know emerald ash borer is on the horizon so there is some urgency to get a healthy population up, some which can then withstand it. We can't deal with both simultaneously."

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