Control of fire blight in the apple orchard and development of bacteriophages as biological control agents

Project code: MU03-PATH02

Project Lead

Antonet Svircev - Agriculture and Agri-Food Canada.

Objective

To identify and develop bacteriophages as biological control agents, and optimize scale up and delivery systems for this novel product for management of the fire blight pathogen, Erwinia amylovora.

Summary of Results

Fire blight is a devastating disease of apple and pear trees caused by the bacterium Erwinia amylovora. As the name of the disease suggests, infected tissue appears blighted or scorched, and the pathogen is capable of rapidly destroying whole trees, causing significant economic loss to producers. Streptomycin is the treatment of choice for this disease, however pathogenic strains resistant to this antibiotic are now appearing in some of the major apple and pear growing regions of North America. This three year project was initiated to examine the feasibility of using bacteriophages, viruses which attack bacteria, to control fire blight in the orchard, with the aim of achieving efficacy similar to that possible with streptomycin. Seven bacteriophage isolates with high levels of virulence specific to the fireblight pathogen were identified, cultured, and tested for efficacy in laboratory, and in field assays in comparison with streptomycin and recently registered suppression products BlightBan® and Bloomtime®. The researchers established sound protocols for the growth and processing of the 7 phages that form the basis of the system and have developed a novel bacterial carrier that allows phage survival and multiplication in the blossom. In addition, the carrier bacteria act as a biological agent, producing an antibiotic substance. Field trials showed that phage : carrier system capable of efficacies comparable to commercial biologicals BlightBan® and Bloomtime®, and in some cases as efficacious as streptomycin.

With the generation within this project of the full genomic sequence for one of the phage isolates, molecular detection techniques using real time PCR to identify and quantify microbial populations in situ were developed. A unique protocol and buffer system allowed the development of specific and robust primer sets and probes for multiplex real time detection of phage isolates, carrier bacteria and pathogen. These tools were used to show that phage populations actually increase on the carrier bacteria, and that they then preferentially attack the pathogen when it is introduced into the system.

The project has demonstrated that bacteriophages have the potential to be developed into a novel and highly effective biological control system for the control of the fire blight pathogen. Preliminary host range studies demonstrate that although the phages are specific to a single species of bacterium, they are somewhat "promiscuous" in that they have the ability to attack E. amylovora pathogen isolates from different geographical areas. This indicates that the phage cocktails have the potential to be a "universal" control, not requiring regional adaptations.

Preliminary discussions have been conducted with potential commercial partners for the development of the technology, and consultations with the federal regulator regarding regulatory requirements for the product are planned. Work is also planned to develop formulation / encapsulation strategies to improve survival in the blossom and to facilitate scale-up production.

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