DETECTION OF ERWINIA AMYLOVORA STRAINS WITH REDUCED SENSITIVITY TO CURRENTLY REGISTERED ANTIBIOTICS AND MANAGEMENT OF FIRE BLIGHT OF POME FRUITS USING KASUGAMYCIN IN INTEGRATED STRATEGIES

Kasugamycin is an aminoglycoside antibiotic that we identified for registration against fire blight and other bacterial diseases in the United States. Kasugamycin will be the first antibiotic introduced in over 35 years for controlling phytobacterial diseases and it has a different mode of action from other antibiotics currently registered. In surveys of California pear orchards, ca. 50% of the isolates of Erwinia amylovora evaluated were found to be resistant to streptomycin. In addition, isolates that were less sensitive to oxytetracycline were detected in one location. All isolates were sensitive to kasugamycin and a sensitivity baseline was developed using over 100 strains. In multiple field trials on pear and apple over three years at several locations, kasugamycin was found to be highly effective in managing fire blight. Repeated sampling of E. amylovora from diseased blossoms from these small-scale field trials indicated no change in sensitivity to the antibiotic. Because of the potential of resistance development in pathogen populations to antibiotics, resistance management studies were pursued using rotations of antibiotics with biological controls and broad-spectrum copper bactericides. In addition, ethylene-bis-dithiocarbamates and other fungicides such as captan were evaluated in vitro and in field studies. In vitro studies indicated that these fungicides were inhibitory and combinations of kasugamycin with these fungicides were efficacious in field trials. Integration of copper bactericides, biological controls, fungicides and antibiotics were highly effective and reduced the total use of any one treatment per season. These resistance management strategies are suggested for labeled use from the onset of introduction of kasugamycin against fire blight and other bacterial diseases.