oxytetracycline--anhydrous and kasugamycin

We assessed the effect of three antibiotics (streptomycin, oxytetracycline, and kasugamycin) on populations of the fire blight pathogen

Topics: Aminoglycosides; Erwinia amylovora; Flowers; Malus; Oxytetracycline; Plant Diseases; Population Dynamics; Streptomycin

Baseline sensitivities were established for kasugamycin and oxytetracycline for 147 strains of Pseudomonas savastanoi pv. savastanoi collected from olive knots throughout California. Minimum inhibitory concentrations for ≥95% growth inhibition ranged from 1.86 to 11.52 and 0.13 to 0.40 µg/ml for kasugamycin and oxytetracycline, respectively. In copper sensitivity evaluations, 95.3% of the strains collected grew at concentrations of metallic copper equivalent (MCE) of <20 µg/ml, 2.7% grew at MCE between 20 and 30 µg/ml (moderately sensitive), and 2% grew at MCE of 150 µg/ml (resistant). Copper resistance was never reported previously in the olive knot pathogen, and pathogenicity studies confirmed a high virulence of the copper-resistant strains. In comparative field studies, kasugamycin at 200 µg/ml performed equally to the standard copper hydroxide treatment (MCE of 1,260 µg/ml) for reducing knot development on lateral wounds of Arbequina and Manzanillo olive inoculated with a copper-sensitive strain and was better than copper using a highly copper-resistant strain. Oxytetracycline at 200 µg/ml was not as effective as copper or kasugamycin but significantly reduced the disease as compared with the untreated control. Field studies on application timings of copper, kasugamycin, and copper-kasugamycin mixtures to inoculated wounds indicated that treatments within 24 h of inoculation resulted in higher disease control than applications at later times. In greenhouse trials, copper or copper-kasugamycin applied to wounds 7 days before inoculation persisted and reduced knot incidence by >50%. Our findings indicate that kasugamycin is an effective bactericide for controlling olive knot and that the time of any bactericide application after inoculation is critical in managing the disease.

Topics: Aminoglycosides; Anti-Bacterial Agents; California; Copper; Olea; Oxytetracycline; Plant Diseases; Pseudomonas