Potato Brown Rot

Ralstonia solanacearum contamination of Scottish rivers: Identifying the risks to high-grade seed production

Project start and end dates:  01/11/2003 – 31/10/2006

Project collaborators: Fera, York, UK; James Hutton Institute, Dundee, UK; SASA

Funding from: The Flexible Fund (now Contract Research Fund) of the Scottish Government’s Directorate for Rural & Environment Research and Analysis

Potato brown rot, caused by the bacterium Ralstonia solanacearum, has never been found in Scottish potatoes, however it was found in the Tay river system in 2000 in an area of high grade potato seed production. Restrictions were placed on potato production in this area to prevent its spread and a programme completed in 2004 to eradicate the bacterium from this watercourse.

This project was born out of this finding and its objectives were to determine the likelihood that further Scottish rivers may become contaminated in future with R. solanacearum, paying particular attention to river characteristics, the diversity of the aquatic secondary host (Solanum dulcamara) and the pathogen itself. These data were then used to determine whether such contamination could pose a significant risk to the health of potato crops in Scotland.

In summary, it was found that Scotland’s one case of river contamination with R. solanacearum occurred as a single or limited event. Surveys indicated that very few rivers in Scotland mimic the profile of this previously infested water course and as a consequence the risk of additional infestations was judged to be low in future years. However, as a precaution, all rivers which share key characteristics with the infested river are now included in Scotland’s annual river survey for R. solanacearum. Further work demonstrated that R. solanacearum is capable of colonising potatoes under Scottish conditions and all popular varieties are susceptible to the disease. It is of concern that should brown rot ever be introduced into Scotland, symptoms are unlikely to be evident in the growing plant or harvested tubers as it is likely that potatoes will become infected with low levels of inoculum and field conditions will seldom reach the elevated temperatures required for rapid progression of infection and symptom expression.  This finding reaffirms the continuing requirement to conduct post-harvest tuber testing.

Further details can be obtained from Gerry Saddler on 0131 244 8925 or by email.