Survival Studies with the Fire Blight Pathogen Erwinia amylovora in Soil and in a Soil-inhabiting Insect

The survival of Erwinia amylovora in soil and in the soil-inhabiting insect Folsomia candida was investigated. Although E. amylovora is an air-borne pathogen, it may reach the soil with rain and other dissemination events. The pathogen was selected on agar plates with two antibiotics and identified by its characteristic colony morphology on minimal agar with copper ions and confirmed by polymerase chain reaction assays. Rates of bacterial decline were much higher in non-sterile than in sterile soil, where the number of living bacteria was stable over 11 weeks. It declined rapidly in untreated soil from a field, and the pathogen was no longer detected 5 weeks after inoculation. Soil-living microarthropods such as F. candida (Collembola) contain large amounts of bacteria in their gut. When fed with gfp-labelled E. amylovora, the pathogen was digested in the gut within a few days, contributing to the decrease of the bacterial population in the soil and thus preventing bacterial distribution by insects.