New hope for ash trees ‘evolving resistance to deadly disease'

Telegraph

5 hours ago

Ash trees are finally mounting a fightback against ash dieback disease, a study has found.
The fungal infection has devastated UK ash populations since it arrived on British shores more than a decade ago, with experts warning it could wipe out the species.
A study by the Royal Botanic Gardens, Kew, and Queen Mary, University of London tracked how the disease was affecting an ancient woodland in Surrey.
Ash dieback has ravaged the Marden Park wood since 2012 with the majority of trees being infected. Dieback causes blackened leaves, stunted growth and shrivelled roots.
But a comparison of the health and genes of trees that matured before 2012 against recent saplings discovered evolution in action, which is making young trees more resilient.
The modern plants had different variations of almost 8,000 genes, accrued by natural selection, which made them more robust, scientists found.
A population's range of genes emerges naturally and randomly, but only those that are advantageous survive long enough to reproduce. Over several generations, genes that make an organism vulnerable die out, and advantageous genes and traits persist in the population.
The new study found that this process weeded out almost a third of the newest ash trees, leaving the 69 per cent that were genetically better able to withstand ash dieback.
The end result is that current juvenile ash trees in this woodland are better able to combat and less likely to die from the disease.
Glimmer of hope against extinction
This offers a glimmer of hope that the British native ash tree, known as Fraxinus excelsior, will not go extinct as some experts had feared.
Ash dieback is caused by the fungus Hymenoscyphus fraxineus and arrived in Britain from Asia in 2012, prompting an emergency Cobra meeting.
British ash trees are uniquely vulnerable to the disease, which does not harm other ash species, including those found on mainland Europe.
The disease has since wreaked havoc across the British countryside, leaving behind skeletal remains of dying ash trees.
Previous predictions estimated that up to 85 per cent of ash trees in the UK would succumb to the disease, with none displaying complete immunity.
They say it also demonstrates this process works even when a certain trait, such as disease protection, is created by lots of different genes, and not just a single chunk of DNA.
Dr Carey Metheringham, whose PhD research included the study, said: 'Thanks to natural selection, future generations of ash should have a better chance of withstanding infection.'
But she also warned that while natural selection is showing signs of an ash fightback, it may not be enough on its own to overcome the dieback threat.
Evolution may not be enough
'Natural selection alone may not be enough to produce fully resistant trees,' Ms Metheringham added.
'The existing genetic variation in the ash population may be too low, and as the trees become scarcer, the rate of selection could slow.
' Human intervention, such as selective breeding and the protection of young trees from deer grazing, may be required to accelerate evolutionary change.'
Additional steps could be needed to prevent ash from facing the same extinction threat as the elm tree, which is being decimated by Dutch elm disease.
The study was largely funded by the Department for Environment, Food and Rural Affairs, which is also leading other work to try and help the ash tree.
The new study is published in the journal Science.