Scientists have made a key discovery into the genetics of the bacteria
that causes blackleg, an economically damaging disease of potatoes, that
could lead to new ways to fight the disease.
The researchers at the University of Cambridge, funded by the
Biotechnology and Biological Sciences Research Council (BBSRC), found
that if a particular gene is inactivated in the bacterium Erwinia
carotovora, its ability to damage the plant and cause disease is
severely impeded. The research was recently published in the Journal of
Bacteriology.

Erwinia carotovora can cause disease in a wide range of plants,
including carrots, tomatoes and onions, but is best known in temperate
regions for causing blackleg and soft rot in potatoes. Its success
partly lies in its ability to produce enzymes which break down its
host?s cell walls. The degraded cell walls provide nutrients to the
bacterium, and so aid its survival and growth.

The Cambridge researchers discovered that if they inactivated a gene
called relA, which helps the bacteria recognise when nutrients are
running low, then the bacteria?s ability to export enzymes to break down
the plant?s cell walls is also abolished.

Research leader Dr Martin Welch explains: ?Blackleg is a significant
economic problem, substantially reducing crop yields.

?We have shown that the production of cell wall degrading enzymes is
genetically linked to not only signalling abilities but also to the
bacterium?s nutritional status. This has important implications for
researchers looking for new ways to control the disease. By improving
our understanding of how Erwinia carotovora rots the plant, we can
reveal additional, possibly novel targets for the eventual development
of anti-rot agents. We have also opened up the potential to develop
pesticides.?

Dr Mike Storey, R&D Director of the British Potato Council, commented in
response to the research findings: "Blackleg is one of the key diseases
across all sectors of the British potato industry. The findings from the
University of Cambridge are important as they could offer novel
solutions, both to help store potatoes and to control the disease.

?Soft rots in particular are a concern for many crops going in store
this season because of the warm and wet growing conditions. We rely on
careful storage management as most varieties of potato have no inbuilt
resistance to soft rot and there are no available pesticides."
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