STUDIES ON ANTIBIOTIC RESISTANCE OF ERWINIA AMYLOVORA AND COPPER-BASED PAINT FOR MANAGEMENT OF FIRE BLIGHT DISEASE

Katelyn Brittani Kiick

doi:10.7273/000006944

Erwinia amylovora is one of the most economically impactful plant pathogens nationwide and in the Pacific Northwest region. Pruning infected shoots and/or cankers throughout spring and summer is commonly used to halt the spread of the disease by reducing the amount of inoculum present in the field. Although very effective, pruning is also labor intensive and costly, and infection can continue to develop or spread between trees if the infection is not removed completely. Copper, a widely used chemical product with bactericidal properties against E. amylovora, is commonly used to treat fire blight. The first goal of this study was to investigate the efficacy of copper-based paint treatments to protect cut wounds. Our results showed that copper, by itself and in combination with latex paint, can provide protection against E. amylovora infections when applied directly to cut wound sites prior to inoculation. By itself and in combination with latex paint, we saw a 55-70% decrease of plants displaying symptoms in the 2022 trial. We also saw 88% shorter necrotic lesions on average, when copper was applied by itself, compared to the control. In contrast, 100% of the plants during both years displayed symptoms when treatments were applied post-inoculation. Most significantly, plants treated with copper in latex paint, and applied after inoculation had necrotic lesions that were between 70-109% longer than when compared to the control. When applied prior to the development of an infection, copper by itself and in combination with latex paint provided the best protection out of the seven methods assayed against the development of the disease. Widespread overuse of streptomycin to combat fire blight has led to the development of streptomycin resistance in multiple areas across the U.S. Increased usage of other antibiotics such as kasugamycin and oxytetracycline has led to concerns over resistance developing against these antibiotics. Antibiotic resistance was last officially reported in Washington State in 1991; thus, the second goal of this study was to determine the status of resistance to antibiotics used in Washington state to treat fire blight, including streptomycin, kasugamycin and oxytetracycline. There was no resistance found for streptomycin or oxytetracycline. We discovered 38 kasugamycin-resistant strains, a concern since there are no previous reports of kasugaymcin resistance in central Washington state. Sequence comparison of the ksgA gene for each strain revealed no differences, indicating the source of antibiotic resistance is not due to a mutation in the ksgA gene. Additional research is needed to identify the exact mechanism behind the resistance. However, the results from this study should help growers as they develop new management plans.

STUDIES ON ANTIBIOTIC RESISTANCE OF ERWINIA AMYLOVORA AND COPPER-BASED PAINT FOR MANAGEMENT OF FIRE BLIGHT DISEASE

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