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Category: Applied and Industrial Microbiology
Bacteriophages for Control of Phytopathogens in Food Production Systems, Page 1 of 2
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This chapter discusses some of the novel methods and technologies implemented in the search for phage biopesticides in agricultural food production systems. It is divided according to agriculturally related application lines. The first section summarizes the historic and current state of phage biopesticides. Most control strategies focus on the suppression of Erwinia amylovora populations in the flower. This is followed by discussions of specific pathogens and application environments in which phages have been used. The third section examines the impact of bacteriophages on soil bacteria located in the rhizosphere and phylloplane, and the potential consequences to plant health and yield. The final section discusses general points to consider for the development of phage biopesticides in agriculture. The bulk of phage therapeutic research and commercial development focuses on the prevention of human pathogens in the food production pipeline. In the current regulatory environment, these types of phage therapies would have difficulty passing through the regulatory system. The success of a phage therapy against any particular disease also depends on the availability of many phages that, together, are effective against most or all strains of the causative agent.
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Erwinia sp. phage biopesticides isolated from orchard environment belong to the Myo- (left), Podo- (bottom right), and Siphoviridae (top right). Marker = 100 nm.
Sequential processes and decisions made for the isolation of bacteriophage carrier P. agglomerans isolates. Isolates were selected on the basis of culturability and ability to produce high-titer phage solutions with Erwinia sp. bacteriophages in the culture collection. (Adapted from Lehman [2007] .)
Effect of phage-carrier combinations on disease severity in forced pear blossom assays, given as mean ± 95% confidence limits for three replications (10 blossoms per replication). Four phages were applied with the carrier using a multiplicity of infection (MOI) of 2 and then again using an MOI of 20. These eight phage treatments, along with the carrier and phosphate buffer (PB) control, were repeated twice: once where 3 h elapsed between treatment and pathogen application (left-hand side) and once where the pathogen was applied immediately after treatment (right-hand side). All phage and carrier treatments except those marked with ‡ resulted in significantly less severe disease than the PB control. Phage-carrier treatments marked with * were significantly better than the carrier alone.
Incidence of fire blight in a 4-year-old Gala apple orchard. Posttreatment, trees treated with buffer (controls) and all active treatments were artificially inoculated with 106 CFU/ml of E. amylovora. BlightBan C9-1 (commercial biological control agent), two carrier-phage treatments, and streptomycin treatments marked with * caused significant reduction in disease incidence relative to the control (P < 0.01). The phage carrier was the orchard-isolated P. agglomerans EH21-5. (Reprinted with permission of S. M. Lehman.)
Electron micrographs showing (left) the infection of Xanthomonas sp. bacterium by phages, and (right) individual phages belonging to the Podoviridae (top right) and Myoviridae (bottom right). Marker = 100 nm. (Courtesy of B. Balogh and J. Jones.)
Effect of formulations on the survival of Xanthomonas sp. bacteriophages in the tomato canopy under field conditions. Experimental groups are distinguished as Silwet (circle), casein (diamond), pregelatinized corn flour (triangle), and nonformulated (square). (Reprinted with permission of B. Balogh and J. Jones.)
The biopesticide value chain was developed at Agriculture and Agri-Food Canada by S. Boyetchko. The chain summarizes the multistep sequential processes and the go/no-go decision processes required in the development of a biopesticide. The main steps in the chain involve bioprospecting, determination of biological and environmental fate, biopesticide optimization, and technology scale-up. (Reprinted from Bailey et al. [2009] with permission of the publisher.)
Effects of phage treatment on bacterial spot in peach orchards a