Development of antagonistic bacteria for field control of fire blight

Flower infections caused by Erwinia amylovora can be prevented only during the short period of epiphytic colonization. Bacterial antagonists like Erwinia tasmaniensis and Bacillus spp. are able to repress E. amylovora growth at this initial stage and prevent further intrusion of the pathogen. They can be applied as biological control agents if a suitable formulation can be produced. To investigate inhibitory effects of different antagonists and dried formulations, we used several test systems in the laboratory, including co-cultivation experiments, agar diffusion assay and detached-flower assays. A luminescent reporter strain of E. amylovora was used to distinguish between pathogen and antagonist growth. In laboratory studies, application of dry formulations was as efficient as with antagonists derived from batch culture. Samples from test-formulations were also applied in field trials according to EPPO guideline 1/166.