Absence of lysogeny in wild populations of E rwinia amylovora and P antoea agglomerans

Lytic bacteriophages are in development as biological control agents for the prevention of fire blight disease caused by E rwinia amylovora . Temperate phages should be excluded as biologicals since lysogeny produces the dual risks of host resistance to phage attack and the transduction of virulence determinants between bacteria. The extent of lysogeny was estimated in wild populations of E . amylovora and P antoea agglomerans with real–time polymerase chain reaction primers developed to detect E . amylovora phages belonging to the M yoviridae and P odoviridae families. P antoea agglomerans , an orchard epiphyte, is easily infected by E rwinia spp. phages, and it serves as a carrier in the development of the phage‐mediated biological control agent. Screening of 161 E . amylovora isolates from 16 distinct geographical areas in N orth A merica, E urope, N orth A frica and N ew Z ealand and 82 P . agglomerans isolates from southern O ntario, C anada showed that none possessed prophage. Unstable phage resistant clones or lysogens were produced under laboratory conditions. Additionally, a stable lysogen was recovered from infection of bacterial isolate Ea110R with P odoviridae phage ΦEa35‐20. These laboratory observations suggested that while lysogeny is possible in E . amylovora , it is rare or absent in natural populations, and there is a minimal risk associated with lysogenic conversion and transduction by E rwinia spp. phages.