Fighting Fire Blight

David Manly
September 24, 2012
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September 24, 2012 – Fire blight is a bacterial disease that is a large threat to commercial pear and apple trees. The bacteria (Erwinia amylovora) are very difficult to control and the standard of applying the antibiotic streptomycin to the plant is not 100 per cent effective. However, with the increased risks of the bacteria acquiring resistance (and the general decline of using antibiotics in agriculture), alternatives are currently being explored.

Dr. Antonet Svircev, a research scientist with Agriculture and Agri-Food Canada (AAFC), and his team have discovered a novel and environmentally friendly approach to control this disease and reduce the damage done by 50 per cent.

Working with researchers at AAFC’s Pacific Agri-Food Research Centre (Julie Boulé, Dr. Peter Sholberg and biologist Dan O’Gorman) and Dr. Alan Castle at Brock University, Dr. Svircev discovered that two commonly found orchard microorganisms – a bacterium and a bacteriophage – offer promising results in fighting this disease.

A bacteriophage (or a phage) is an organism that only attacks specific kinds of bacteria. The phage takes control of the bacteria’s own machinery to create copies of itself before destroying the bacteria and releasing its contents (anywhere from 50 to 200 new phages). This cycle then repeats over and over until the bacteria are gone.

Therefore, Dr. Svircev thought this would be a new way to biological control the fire blight bacteria. By purposely infecting Pantoea agglomerans (which itself is a control agent of fire blight) with the phage and dosing the plant with the mixture, the researchers could produce a large number of phages at one time to control and eliminate E. amylovora.

And the results were far better than anyone expected.

“The phages multiplied on the carrier reaching high population numbers and once the fire blight pathogen appeared, the phages preferentially attacked the fire blight bacteria and decreased the populations on the blossom,” said Dr. Svircev. “The decreased population of the pathogen by 50 per cent led to no infections of the blossom.”

The next step of the research is to expand to large-scale field trials using the carrier and a mixture of phage to prevent the fire blight from becoming resistant. The ultimate goal is to develop a biopesticide that will be both highly effective and consistent. However, Dr. Svircev said that there are still some problems that need to be addressed before commercialization.

“The biopesticides need to be applied well ahead of the fire blight bacterium and need for consistent field efficacy from year to year,” he added. “The material also needs to be stored in a fridge rather than in a barn storage area.”

But, the phage-carrier is an environmentally friendly alternative for plant disease control that can be easily included into present fire blight management programs. In addition, research at Dr. Svircev’s lab has shown that phage-host resistance is not a common phenomenon in the fire blight pathogen and phage-carrier system.

The AAFC notes that these brands of biopesticides are not stand alone products, but are very effective at reducing the pathogen population in the open blossoms. While the phage-carrier biopesticide is still in development, AAFC’s goal is to achieve improved control with this double-acting biopesticide.

This work could benefit Canadian farmers by helping to reduce the damage caused by fire blight, thereby protecting crops, saving money and helping to minimize loss.

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