Pathogen Profiles

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Molecular Plant Pathology - Pathogen Profiles


Soft rot erwiniae: from genes to genomes

Ian K. Toth*, Kenneth S. Bell, Maria C. Holeva and Paul R. J. Birch

Plant-Pathogen Interactions Programme, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK


Summary: The soft rot erwiniae, Erwinia carotovora ssp. atroseptica (Eca), E. carotovora ssp. carotovora (Ecc) and E. chrysanthemi (Ech) are major bacterial pathogens of potato and other crops world-wide. We currently understand much about how these bacteria attack plants and protect themselves against plant defences. However, the processes underlying the establishment of infection, differences in host range and their ability to survive when not causing disease, largely remain a mystery. This review will focus on our current knowledge of pathogenesis in these organisms and discuss how modern genomic approaches, including complete genome sequencing of Eca and Ech, may open the door to a new understanding of the potential subtlety and complexity of soft rot erwiniae and their interactions with plants.
Taxonomy: The soft rot erwiniae are members of the Enterobacteriaceae, along with other plant pathogens such as Erwinia amylovora and human pathogens such as Escherichia coli, Salmonella spp. and Yersinia spp. Although the genus name Erwinia is most often used to describe the group, an alternative genus name Pectobacterium was recently proposed for the soft rot species.
Host Range: Ech mainly affects crops and other plants in tropical and subtropical regions and has a wide host range that includes potato and the important model host African violet (Saintpaulia ionantha). Ecc affects crops and other plants in subtropical and temperate regions and has probably the widest host range, which also includes potato. Eca, on the other hand, has a host range limited almost exclusively to potato in temperate regions only.
Disease symptoms: Soft rot erwiniae cause general tissue maceration, termed soft rot disease, through the production of plant cell wall degrading enzymes. Environmental factors such as temperature, low oxygen concentration and free water play an essential role in disease development. On potato, and possibly other plants, disease symptoms may differ, e.g. blackleg disease is associated more with Eca and Ech than with Ecc.
Useful websites: www.scri.sari.ac.uk/TiPP/Erwinia.htm
www.ahabs.wisc.edu:16080/pernalab/erwinia/index.htm

www.tigr.org/tdb/mdb/mdbinprogress.html

www.sanger.ac.uk/Projects/E_carotovora/


(a) Comparison of healthy potato plant (left) and plant infected with Erwinia carotovora ssp. atroseptica (right) showing severe wilting and stem rot due to blackleg disease (see base of stem). (b) African violet (Saintpaulia ionantha) leaf infected with Erwinia chrysanthemi. (c) Growth of soft rot erwinia on crystal violet pectate (CVP) medium showing characteristic cavities formed by the production of exoenzymes. (d) In planta virulence screening assay by stab inoculation of Erwinia carotovora subsp. atroseptica into potato stems showing increasing severity from left to right.

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