Saturday, 14 January 2017

Genetics to the Rescue: The Fight Against Ash Dieback

Ash dieback is a fungal disease that causes ash trees to lose leaves from their canopy. It is found throughout large swaths of Europe; after being discovered in Poland back in 1992, it was later found in Lithuania, Latvia, Estonia, Denmark, Germany, Austria, as well as many other countries. It was first documented in the UK in 2012, which led the government to impose a ban on European ash imports.

The Causal Organism

The disease, which is caused by the fungus Hymenoscyphus fraxinea, does not always kill the trees it infects, but most mature trees eventually succumb after unsuccessfully battling the fungus for several years. It is particularly destructive to immature trees, which have fewer resources to mobilize and leaves to spare in the conflict. It typically first appears as a series of necrotic lesions, which persist for several years. Eventually, these lesions can encroach beneath the bark, where they can begin affecting the xylem (wood) of the trees.

Management Strategies

Thus far, forest managers and researchers have had little success in combatting the fungus. Workers formerly tried to destroy Infected trees to halt the spread of the disease, but this was not an effective strategy, because the fungus lives in the leaf litter carpeting the forest floor – tree removal to eradicate the fungus is like trying to empty the ocean one bucket at a time.

Natural Resistance

However, researchers have long observed that some ash trees exhibit a natural resistance to the pathogen. The hope is that these naturally resistant trees could be cultivated en masse, and then used to replace non-resistant ash trees growing throughout the landscape. However, this has not proved to be an easy task. Fortunately, soldiers in the fight against ash dieback just added another weapon to their arsenal.

Genetics to the Rescue

Researchers at Queen Mary University of London recently sequenced the genome of the European ash tree (Fraxinus excelsior). Their work produced a few novel, if not helpful, bits of information, such as the fact that approximately 25 percent of the ash tree’s genome is comprised of genes that only occur in ash trees.

However, the true value from the study will be best realized when the researchers are able to compare the genes of the ash trees in their study with those of populations that exhibit some resistance to the disease (for example, Denmark is home to a small colony of resistant trees). This should allow the researchers to determine which genes are responsible for the resistance, and perhaps eventually manipulate the genetic code of ash trees to impart resistance upon them.

If you have any concerns about the health of your trees, contact your local tree surgeon today.

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