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‘Gangrene-like’ disease plaguing English oak trees is caused by bacteria and beetles

A deadly disease threatening English oak trees is caused by several bacteria types interacting with beetles that bore through the bark, new research has revealed.

Acute oak decline, which creates cracks in the bark that ooze a dark liquid, has been likened to gangrene and can kill a large tree within five years.

Scientists from Bangor University believe their discovery could help find a cur for the condition which poses an ‘existential threat’ to the iconic species.  

They found that no single bacteria was responsible for the disease, but rather a combination of bacteria types and a beetle that bores through the weakened bark. 

Over the next month the team hope to see whether re-engineering the microbiome within the tree could prevent or even cure the deadly disease, The Times reports. 

Acute Oak Decline (AOD) is a complex disease with many interacting causes including bleeds on the inner and outer bark and nutrients not reaching the canopy.

The ‘bleeds’ on the bark cause wounds that overlie areas of rotting tissue inside the bark that include exit holes from a boring beetle whose larvae mature in the tree. 

These larval galleries of the bark-boring beetle Agrilus biguttatus work in concert with different bacteria and the holes made by their parents, authors found.

The bacteria and boring beetle cause changes to the microbiome inside the tree bark which then causes the disease to spread and eventually kill the tree. 

‘This co-operation was also found between various bacteria in the tree bark which catabolise sugars into ingestible products,’ the authors wrote. 

‘This study highlights the co-operation of complex tree-bacteria-insect interactions that underlie the onset of diseases that threaten global forest biomes.’

‘A complex of micro-organisms act together to cause the really prolific bleeding, which is the main symptom’ of the disease, the authors explained.

The disease can kill an infected oak tree within five years and is mainly found in south-eastern, eastern and central England and parts of Wales.

Drought-prone areas with high levels of nitrogen pollution appear to have the most cases of the disease, according to the Forestry Commission.

Thousands of the trees have been affected with most older than 50-years. 

To find the disease causing bacteria study authors injected different types into samples of an oak tree until they found the combination that triggers the disease. 

‘We’ve tried to disentangle the different interactions that take place. Our work touches on how imbalances in the microbiome can lead to disease,’ study author James McDonald told The Times.

This same technique, used to find out what causes the disease and changes the microbiome of infected trees could hold the key for a cure, researchers say. 

‘We will try and identify the factors that shape and change the microbiome of oak trees, to see if we can engineer them towards a healthy status,’ said McDonald. 

The study ‘Host–microbiota–insect interactions drive emergent virulence in a complex tree disease’, is published in the Proceedings of the Royal Society B. 

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