Ash trees evolving resistance to dieback

Times

16 hours ago

The forces of evolution are helping Britain's ash trees to fight back against a deadly fungus that has threatened to decimate the species, a study suggests.
After ash dieback was first recorded in the UK in 2012 experts warned that the disease had the potential to 'change the landscape for ever' by killing up to 90 per cent of Britain's 150 million ash trees, which in 2019 accounted for about 12 per cent of the nation's broadleaf woodland.
However, analysis suggests that natural selection — the evolutionary process first described by Charles Darwin — is already favouring traits that will help young ash survive.
Ash trees were felled in places such as Lower Woods, Gloucestershire, to limit the spread of dieback
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Scientists from the Royal Botanic Gardens, Kew, and Queen Mary University of London compared older trees with new saplings. They found thousands of genetic differences that appeared to be allowing younger trees to withstand the fungus more successfully than their predecessors.
Professor Richard Buggs, a senior scientist at Kew and co-author of the study, said the research had raised hopes that ash could fare better than Britain's elms, which were all but wiped out by Dutch elm disease.
'These findings suggest that ash will not go the way of the elm in Britain,' Buggs said. 'Elm trees have struggled to evolve to Dutch elm disease [because of low levels of genetic diversity] but ash are showing a very different dynamic because they produce an abundance of [genetically different] seedlings upon which natural selection can act when they are still young.'
Ash dieback causes leaf loss and stem lesions and often results in trees dying. The research team analysed trees in Marden Park wood in Surrey, a site managed by the Woodland Trust. By studying thousands of variants of different genes, they identified subtle changes between generations.
Charles Darwin's theory of evolution proposes individuals within a species most suited to their environment will survive and pass on those benefits to their offspring
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'A tragedy for the trees has been a revelation for scientists, allowing us to show that thousands of genes are contributing to the ash trees' fightback against the fungus,' said Professor Richard Nichols, an evolutionary geneticist at Queen Mary University London.
Even so, the researchers warned that the future of the species in Britain was not guaranteed. 'Natural selection alone may not be enough to produce fully resistant trees. The existing genetic variation in the ash population may be too low and, as the trees become scarcer, the rate of selection could slow,' said Dr Carey Metheringham, an author of the study, which has been published in the journal Science.
'Human intervention, such as selective breeding and the protection of young trees from deer grazing, may be required to accelerate evolutionary change,' Metherington added.