A disease is killing the UK’s ash trees at an alarming rate and, once a tree is infected, there is no known cure. However, scientists may now be one step closer to a solution after unraveling the genome of a resistant ash tree cousin.
Ash die-back disease is a serious infection by the fungus Chalara fraxinea which in turn causes leaf and branch loss. The disease is quite often fatal for the tree and, as the UK has seen, is incredibly difficult to contain because the fungus spores grow and spread on leaf litter on the wind.
So if you can’t cure the fungus or hope to stop its spread, how to combat ash die-back?
The solution scientists have arrived at is breeding trees that are resistant to the spore, and that is precisely the subject of a joint project by the John Innes Centre, the Genome Analysis Centre and the Sainsbury Laboratory.
The researchers have been examining a genus of ash tree known as “Tree 35,” a strain bred in Denmark nearly 100 years ago that has shown an ability to withstand fungal infection even while nearly all other Danish ash strains have been wiped out.
However, the researchers don’t want to simply replace native ashes with the Tree 35 strain because this would result in narrowing the genetic pool that in turn would leave the trees vulnerable to other diseases in the future.
Instead, scientists want to breed Tree 35′s ash die-back resistance into existing stocks and so first needed to identify the key genetic traits that offer this resistance and so set about sequencing the Tree 35 genome.
To do that, they needed to sequence or map out the tree’s entire genome, which is precisely what they have now done. This data is being uploaded to the crowd sourcing website OpenAshDieBack, where experts from around the world will analyze the data to help identify the genes that allow the Tree 35 strain to withstand ash die-back.
The next step will be to incorporate those genes into a breeding program to create resistant, but still UK-native, trees.
How It’s Spread
Ash die-back has been found throughout Europe but hadn’t been observed in the UK until February 2012 when the fungus was detected in trees at a Buckinghamshire, England, nursery that had received stocks from a nursery in the Netherlands.
May 2013 saw what the UK Forestry Commission describes as the “first wider-environment” in south-west Wales, the farthest west site from other known infection sites to date.
The commission puts current confirmed infection numbers at 524 sites in counties including Norfolk, Suffolk, Sussex and Yorkshire. There is also evidence to suggest that the ash die-back is now sporing in the UK, posing an even greater threat to the UK’s estimated 80 million ash trees.
Scientists have also been at work in a government-backed initiative to sequence the genome of the fungus behind ash die-back in hopes that this too can offer important clues about how to defeat the fungus. Unfortunately, neither initiative is likely to lead to a quick solution for ash die-back and will not save existing trees, meaning the situation is likely to get worse before it gets better.
With this, however, there is hope that the UK’s ash tree numbers might one day recover from this fungal onslaught and that future ash die-back outbreaks could be prevented.