Ash dieback resilience genes uncovered
The genetic changes that protect ash trees against ash dieback disease have been uncovered by UK scientists...
Ash dieback is a fungal infection that arrived from Europe in recent years and threatens to wipe out 95% of the UK’s ash tree population. But what is special about the 5% of native ash trees that do not succumb, and could they hold the key to protecting our ash stocks?
Richard Nichols, from Queen Mary University of London, who carried out the new study explains that they identified “no single gene involved in resistance to this disease, but genes spread all across the chromosomes. Hundreds, perhaps thousands, of genes, each with a small effect, contribute to the resilience of some trees.”
“When the disease arrives, it’s catastrophic. Around about 70% of the ash trees in a woodland will die. That includes the well established, mature trees. Across the country, that amounts to about 70 million trees, a major component of our woodland.”
The study, in collaboration with scientists from the Royal Botanic Gardens, Kew, was based on 1250 independent samples collected by Forest Research in a mass screening trial, which involved planting 150,000 trees in various locations around the south of Britain.
Through DNA-sequencing technology, they extracted the genetic makeup of the sampled trees.
“We had a whole series of [genetic] reads from trees which had been affected and another of series of reads from trees which were unaffected. And we compared the two to look for differences,” Nichols explains.
Once they identified which genes are present only in trees that are immune to dieback, they created a resilience score based on how many of these genes were present in a particular tree’s genome.
“When a tree had a really high score, then with 80% probability, it was one of the more resilient trees,” Nichols explains.
Until now, the only measure taken to stop dieback was to chop down all ash trees in a woodland as soon as the disease was diagnosed. But with this new, immediately relevant information, the resilient trees can be identified and saved.
“If some trees are going to do well, and would be good to reseed the woodland, then we want to be able to identify those and not cut them down.” Nichols adds that they also want to “breed trees which will be useful to repopulate woodlands which would be resilient to the disease.”
This study also testifies to the importance of genetic variance in species. “This is a really important example of why our conservation efforts should maintain large diverse populations. Because if our ash trees had been one cultivar [a single variety of tree] that had been planted all over the country, we wouldn’t have this natural reservoir of resilience.”