Conservation and Environment
Investigating horse chestnut bleeding canker Wraysbury bi-annual news - pdf reader required

Trees and woodlands play a critical role in sustaining our environment. One of the Forestry Commissionís major objectives is the long-term sustainable management of trees and woodlands. To do this, we need to address the causes of woodland decline and protect trees from invasive species and diseases.

One new threat is a disease known as bleeding canker of horse chestnut, caused by the bacterium Pseudomonas syringae pv aesculi (Psa). This disease has rapidly become widespread throughout Britain over the past five years, but prior to this had only been reported from India in 1980 on Indian horse chestnut (Aesculus indica). It has now proved to be highly mobile and exceptionally virulent to European horse chestnut (Aesculus hippocastanum).




Forest Research

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Research is underway to provide an accurate diagnosis of this pathogen and underpin management strategies to combat the disease. A technique called real-time polymerase chain reaction (PCR) has been developed and is being used to detect the levels of Psa on infected trees and their surroundings. PCR is a highly specific, sensitive and rapid method of identifying pathogens based on the detection of specific and highly characteristic segments of DNA, which can allow us to track how such organisms survive and spread in the environment. 

Little was known previously about what natural resistance horse chestnut populations may have to Psa, but observational evidence indicates that even in heavily affected locations some trees remain healthy and symptom free. Disease-free horse chestnuts have been propagated and will be tested for disease resistance in inoculation trials and compared against other disease-prone individuals.

This research will ultimately guide management and mitigation strategies and the molecular techniques developed will also be applicable to the study of other important tree diseases. For more information, visit

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