Pathogenicity and virulence of <i>Erwinia amylovora</i>

Fire blight, caused by the bacterial pathogen Erwinia amylovora, is the most significant global threat to commercial apple and pear production. Outbreaks resulting in flower infection cause yield losses accompanied by internal systemic spread of pathogen cells through trees that can lead to tree death in a single season. The type III secretion system and the exopolysaccharide (EPS) amylovoran are pathogenicity factors, and biofilm formation in leaf xylem is a critical virulence factor. We review our current knowledge of E. amylovora pathogenesis and how pathogenesis strategies intersect and facilitate systemic movement in the host. Fire blight management remains extremely difficult due to the high susceptibility of host plants and the aggressive virulence of the pathogen. We suggest that future management will rely on innovative strategies for resistance breeding or those that directly target bacterial populations and condition the host by eliciting a resistance response prior to pathogen arrival.