During the past couple of months, there have been four invasions of ralstonia bacteria at rose companies in the Netherlands. In two cases, it concerned new locations. At two of the thirteen companies that had been contaminated before, inspectors found the bacteria again.
The tropical variant of Ralstonia solanacearum was detected at rose companies for the first time in August 2015. Inspectors reported in February 2016 that there were 13 rose companies (nine growers and four breeders/propagators) that were affected by the disease, also known as brown rot. It concerned mostly young plant material for cut roses. Clearing and disinfection took place, in line with the 2000/29/EC phyto sanitary directive for contamination with this quarantine organism.
Two of the previously cleared companies were inspected, and it turned out that the bacteria were still present in their crops. In the meantime, the so-called elimination programme has been started again. One of the companies is now declared free of the bacteria, the other company recently cleared and disinfected and the authorities are still investigating whether these measures were successful.
In July 2016, another rose company infection was discovered, when the authorities received a (compulsory) notice from a private laboratory. At the end of September 2016, the bacteria were found at another rose propagating company as well. This brought the total number of infected companies to 15. Three companies have since terminated their cultivation of cut roses.
As preventive clearing is often part of the measures, it’s hard to determine the exact extent of the damage. A rough estimate is 18 hectares of cleared greenhouses. Once a company has been contaminated with the bacteria, they can’t do any propagating for a few months. The total damage runs into millions of euros.
Source of infection still unknown
After the elimination programme has been completed, the cleared and disinfected companies are continued to be monitored for a while. The authorities haven’t found the source of the infection yet. They are investigating all isolates from infected samples of rose and water taken from the affected companies. Results are expected to be published in autumn. What’s known so far is that the contamination of the roses in the Netherlands was all caused by the same genotype Ralstonia solanacearum (type 1, the tropical variant).
