Potato ring rot is caused by the Gram-positive bacterium Clavibacter michiganensis ssp. sepedonicus and is an economically important disease in potatoes. There are currently no strategies to combat this disease once it has established itseif in a crop. Fu rthermore, latent infections are common and difficult to deteet because of the insufficient diagnostic methods available and because of low numbers of bacterial celis in latently infeeted potato tissues. The factors that trigger the outbreak of the diseas e are not known. This project aims at creating basie knowledge of the bacterium and at identifying genes and gene products that play a role during the infection process. To achieve the goals, a number of characteristics that may be relevant for the infeet ion process wiIl be studied, such as plasmids, production of extracellular enzymes and production of other extracellular factors such as bacteriocins. In a complementary approach, differential display will be used to identify (unknown ) approach, differen tial display will be used to identify (unknown bacterial genes thatare expressed during infection and outbreak of the disease.