Horse chestnut canker research could provide key to tackling disease

Scientists have decoded the genome of a bacterium that is causing horse chestnut canker.

Bleeding canker on horse chestnut Pic: Forestry Commission
Bleeding canker on horse chestnut Pic: Forestry Commission

Scientists from Forest Research, the University of Reading and The Sainsbury Laboratory (TSL) have decoded the genome of a bacterium causing horse chestnut canker.

In 2002 a new, lethal pathogen — a bacterium called Pseudomonas syringae pv. aesculi (Pae) — appeared in the UK.

Pae causes cankers which bleed like open sores and in severe cases can kill large, mature horse chestnut trees within one or two seasons.

Forestry Commission research has found more than 70% of the trees surveyed in some regions of Britain showed symptoms that indicated or might indicate bleeding canker.

But a partnership of scientists from the three research establishments has decoded the bacterium's genome, unlocking information that can help to inform advice on managing the disease.

Forest Research, the scientific research arm of the Forestry Commission, isolated and led the sequencing of the main British strain of Pae used in the study.

"Detecting the origin of Pae is important from a biosecurity perspective," said Dr Sarah Green, a tree pathologist with Forest Research. "There has been an unprecedented rise in invasive plant diseases, possibly linked to the rise in international travel and in the global plant trade.

"We now have the first clues to the evolutionary origin of the disease and to its ability to spread so fast."

Dr David Studholme, who led the analyses of the DNA sequences at The Sainsbury Laboratory in Norwich, added: "Comparing the genomes of British strains of the bacterium has shown us they are very similar and probably originated from a single introduction into the UK within the past few years."

Before the European epidemic, the only reported case of Pae was in India. A similar strain infects the Indian horse chestnut, but causes only minor lesions in the leaves. The strains that emerged in Europe appear to be more aggressive and attack the woody trunk and branches.

"This pathogen spread quickly through Western Europe and Britain, and the information from the sequencing will help us discover how it is dispersed," said the University of Reading's Dr Rob Jackson.

The differences between the Indian and British strains give the first clues to its virulence on European horse chestnut. The British strains contain additional genes that enable it to live off the sucrose found in the tree sap.

The genome sequence will allow scientists to determine which genes might be necessary for infection of a tree host so they can be targeted to manage the disease.

"Emerging human and animal diseases are routinely sequenced, and this research shows the usefulness of doing the same for plant pathogens," said Dr Studholme. "We can quickly generate large amounts of genetic information on emerging plant diseases that is valuable for combating current and future biosecurity threats."

The research results have been published in the PloS One journal in a paper, Green et al: Comparative genome analysis provides insights into the evolution and adaptation of Pseudomonas syringae pv. Aesculi on Aesculus hippocastanum.


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