Outbreak of Clavibacter michiganensis subsp. sepedonicus in the Netherlands
In the Netherlands, during the 2000 growing-season, Clavibacter michiganensis subsp. sepedonicus (EPPO A2 quarantine pest - causal agent of potato ring rot) has been found in ware potatoes (Solanum tuberosum cv. Première). It can be recalled that an isolated finding had been reported in 1999 (see EPPO RS 99/056). The infection was discovered following the finding of suspect symptoms in the field in mid-July 2000 and was confirmed by the end of September by laboratory testing using the official EU method (EU Council Directive 93/85/EEC). On the farm concerned, 2 fields were planted with seed potatoes cv. Première originating from the same lot. Both crops were found to be infested with ring rot. All other lots of this farm were tested for ring rot and found free. 3 sister lots of the infested lot were grown on other farms in the Netherlands. One of these lots is confirmed to be infected and the 2 other lots are still under investigation. From the results obtained so far, it can be concluded that these 2 sister lots are suspected to be infected with ring rot. The origin of the infection is still under investigation. All necessary measures are imposed on crops, fields and farms concerned to prevent any further spread and to eradicate the disease, according to the EU Council Directive on the control of potato ring rot (93/85/EEC).
It is noted that the ware potato crops, in which ring rot has been found, were grown from seed potatoes having the same origin within the Netherlands. This is the first time that a clonal relationship is identified in the occurrence of ring rot in the Netherlands. Since 1992, surveys for ring rot are conducted in the Netherlands. The results of these surveys and the risk of introduction were evaluated yearly and served as a basis for adjusting the intensity of the survey. This has resulted in a gradual increase of the survey intensity, which was increased even more for the 2000 harvest due to the outbreak reported here. The situation of C. michiganensis subsp. sepedonicus in the Netherlands can be described as: Present: only at a few locations, under eradication.
NPPO of the Netherlands, 2000-10.