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 identi®ed by its characteristic colony morphology on minimal agar with copper ions and con®rmed 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 ®eld, and the pathogen was no longer detected 5 weeks after inoculation. Soil-living micro- arthropods 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.