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Using molecular technology to characterise the biology of Pseudomonas syringae pv. aesculi, causing bleeding canker of horse chestnut

Pseudomonas syringae pv. aesculi Pseudomonas syringae pv. aesculi in culture Bleeding canker lesions


A recently emerging bleeding canker disease, caused by the bacterial pathogen Pseudomonas syringae pv. aesculi (Pae), is threatening European horse chestnut (Aesculus hippocastanum) in northwest Europe. Prior to its recent emergence in Europe, Pae has only been reported causing minor leaf lesions on Indian horse chestnut (Aesculus indica) in northern India. This suggests that Pae may have originated from India and been recently introduced into Europe with devastating effects on European horse chestnut. Due to its virulence and rapidity of spread throughout a high proportion of the horse chestnut population in affected European countries, Pae presents an excellent model pathogen for gaining a greater understanding of bacterial tree diseases.

This project aims to use molecular tools to investigate aspects of the biology of Pae:

  • Real-time PCR will be used to study the processes of infection by Pae as well as its survival and dissemination outside the host.
  • The draft genome sequences of British strains and an Indian strain of Pae have now been generated and will be used to design molecular markers to trace the recent evolution of Pae.
  • The Pae genomic data also include unique genes and genetic pathways implicated in virulence and fitness on a woody host. The biological function of these genes will be explored.

Research objectives

  • Characterise the processes of infection of Pae on the woody parts of horse chestnut.
  • Determine the potential of Pae for survival and dissemination in soil, water and other environmental substrates
  • Use phylogenetic information from a range of Indian and European Pae strains to determine the geographical origin of Pae and its pathways of spread in Europe
  • Determine the biological function of Pae-specific genes which are implicated in virulence on a tree host
  • Build a scientifically sound knowledge base to assist policy decisions on future threats posed by exotic bacterial tree diseases.

Publications and seminar presentations

Publications of specific relevance to this project:

  • Steele, H., Laue, B.E., MacAskill, G.A., Hendry, S.J. & Green, S. (2010). Analysis of the natural infection of European horse chestnut (Aesculus hippocastanum) by Pseudomonas syringae pv. aesculi. Plant Pathology. (In Press).
  • Green, S., Studholme, D.J., Laue, B.E., Dorati, F., Lovell, H., Arnold, D., Cottrell, J.E., Bridgett, S., Blaxter, M., Huitema, E., Thwaites, R., Sharp, P.M., Jackson, R.W. and Kamoun, S. (2010). Comparative genome analysis provides insights into the evolution and adaptation of Pseudomonas syringae pv. aesculi on European horse chestnut. PLoS ONE 5(4): e10224. doi:10.1371/journal.pone.0010224.
  • Green, S., Laue, B., Fossdal, C.G., A’Hara, S. and Cottrell, J. (2009). Infection of horse chestnut (Aesculus hippocastanum) by Pseudomonas syringae pv. aesculi and its detection by quantitative real-time PCR. Plant Pathology 58, 731-744.

Further scientific and practical publications on horse chestnut bleeding canker.

Bacterial bleeding canker of horse chestnut – unravelling its secrets through genomics (PDF-816K)
Presentation given at the Forest Research – Research update seminar (Spring 2010).

Funders and partners

Forestry Commission logo
This work is funded by the Forestry Commission as part of its Monitoring and Biosecurity programme, and the Forest Research CEO Innovation fund.

Forest Research is the industrial partner in a BBSRC-CASE PhD studentship on the evolutionary adaptations of Pseudomonas syringae to woody hosts. The student, Reuben Nowell, will commence in September 2010, and will be supervised by Dr Sarah Green, Forest Research, and Professor Paul Sharp at the Institute of Evolutionary Biology, University of Edinburgh.

Collaboration is also taking place with:

Forestry Commission policy

This has two main aims: the sustainable management of existing forests and woods and a steady expansion of woodland area to provide benefits for society and the environment. The Forestry Commission also has legal powers to prevent the entry of non-endemic pests and diseases of trees.

This project will advance our knowledge of the biology of an important and newly emerging bacterial tree pathogen in relation to its host and environment. Information resulting from this project will help guide the development of policy aimed at protecting Britain’s trees against exotic bacterial diseases.


This project was established in 2008 and is ongoing.


Sarah Green

People involved

  • Dr Joan Cottrell, Forest Research
  • Dr Sarah Green, Forest Research
  • Dr Bridget Laue, Forest Research
  • Grace MacAskill, Forest Research
  • Reuben Nowell, PhD student, University of Edinburgh
  • Professor Paul Sharp, University of Edinburgh

What's of interest

Bleeding in horse chestnut

Bleeding Canker of Horse Chestnut

Practical and scientific information including:

  • Its extent
  • Symptoms
  • Management advice
  • Photos
  • Bibliography