PhD defence - Julie Stenberg Pedersen

As the global population is expected to reach 10 billion people in 2050, food production must increase substantially to meet the rising consumption demands. Food production is affected by numerous factors including bacterial plant diseases affecting the overall crop yield profoundly. Soft Rot Pectobacteriaceae (SRP) are a family of plant pathogenic bacteria affecting a wide variety of crops, highlighting their economic relevance. SRP consists of species within the genera Pectobacterium and Dickeya. SRP are especially known to have an adverse impact in potato production leading to high economic losses in the field, during storage and importantly downgrading seed lots. The epidemiological transmission of SRP has been investigated for almost a century, and several transmission routes are currently suggested. These include latently infected seed tubers, contaminated equipment during harvest or planting, irrigation water, aerosols and insect transmission, whereas latently infected seed tubers are seen as the major disease source. No effective control measures do currently exist, and disease management is primarily based on seed certification systems, together with hygiene and cultivation practices. Several studies have shown bacteriophages (phages) to be promising biocontrol agents against SRP. Phages are viruses of bacteria, obligate parasitic of bacterial cells for viral replication and production. Phages have been indicated as possible biocontrol agents against SRP in potato production, and several studies have shown phages to be able to target SRP when used in vivo. To investigate whether phages may be able to be used as biocontrol agents it is important to isolate and characterize phages targeting SRP in relation to their biocontrol potential, as well as understanding the epidemiological spread regarding disease management and evaluate applied perspectives of phage solutions. This thesis work focused on the epidemiological spread of SRPs in Denmark as well as on the isolation of phages targeting these pathogens and investigated several applied perspectives. SRP strains were isolated during a three-year field study where several clonal clades were found, suggesting a common origin of these pathogens. Several phages were also isolated and characterized, and a combination of phages were tested in relation to applied perspectives focusing on their stability and environmental impact.