In Norway and several other countries there has been a significant increase in potato blackleg disease during the last years. Potato blackleg is an important certifiable disease caused by the bacterium Erwinia carotovora ssp. atroseptica (Eca). Currently , there are no reliable chemical or biological methods to combat the disease once it has established itself in a crop. Furthermore, latent infections are common and difficult to detect. Finally, outbreak of the disease in an infected field is unpredictabl e, because the factors that trigger the outbreak are unknown. This project aims at identifying genes, gene products, and regulatory mechanisms that are potentially related to Eca pathogenicity. Differential display will be used to identify (unknown) bacterial genes that are expressed during infection and outbreak of the disease. In addition, genome-mining will be used to select specif ic genes (enzymes, regulatory mechanisms) for further studies. We will use GFP-labeled strains to study growth of Eca in planta as well as the expression of selected genes during disease development. The results will provide a knowledge basis for developm ent of new diagnostic tools and new strategies for disease management.