Monday, July 27, 2009 - 9:10 AM
S19
A bacteriophage-based biopesticide to control fire blight
Dwayne R. Roach1, Susan M. Lehman2, Alan J. Castle1, and Antonet M. Svircev3. (1) Department of Biological Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, ON L2S 3A1, Canada, (2) Biofilm Laboratory - Clinical and Environmental Microbiology Branch, Centers for Disease Control and Prevention, 1600 Clifton Road NE, Mail Stop C-16, Atlanta, GA 30333, (3) Environmental Health: Biological Control, Agriculture and Agri-Food Canada, 4902 Victoria Avenue North, P.O. Box 6000, Vineland Station, ON L0R 2E0, Canada
Fire blight caused by the bacterium Erwinia amylovora, is a commercially significant disease of apple and pear. The use of phage-based biopesticides is an environmentally responsible alternative to chemical pesticides currently in use. Field trails applying both Erwinia spp. phage and Pantoea agglomerans resulted in 6 out of 13 treatments significantly reducing disease incidence. P. agglomerans is a non-pathogenic orchard epiphyte capable of maintaining a replicating phage population prior to pathogen introduction. Optimal efficacy was achieved with a suspension of phage and epiphyte at 108 units/ml each (ratio of 1:1). Treatment efficacies were also not statistically different from the “gold standard” treatment streptomycin. Multiplex real-time quantitative PCR was used to monitor population ecology during treatments. In treatments with significant disease control, the phage population increased at the expense of the P. agglomerans population. Application of pathogen resulted in a continual increase in phage population now at the expense of the pathogen. The reduction in pathogen population correlated with reduced disease incidence. Studies on capsular polysaccharides (EPS), which may play a protective function against phage attack, were also conducted. A difference in E. amylovora isolate susceptibility to phage attack was found to be influence by EPS production. Phages within the family Podoviridae showed a high efficiency of plating on hosts that produced large amounts of EPS, whereas Myoviridae have similar results but on isolates that produced low amounts of EPS. From this, treatments that match efficient lytic activity to its ideal host should increase treatment efficacy, thereby reducing disease incidence.
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