Copper and streptomycin resistance in bacterial strains isolated from stone fruit orchards in New Zealand

Stone fruit orchards in New Zealand are sprayed with copperbased compounds and streptomycin to control bacterial diseases such as bacterial blast (Pseudomonas syringae pv syringae) and bacterial spot (Xanthomonas arboricola pv pruni) About 50 of the bacteria isolated from nectarines from the orchard at Clyde Research Centre Central Otago in September 2003 were found to be resistant to copper The percentage of strains of P syringae pv syringae isolated in 2004 from nectarines from the same orchard that were resistant to 500 mg/litre of copper was 58 This percentage rose to 92 seven days after treating the trees with copper In 35 of the 48 samples from commercial stone fruit orchards tested more than half of the bacteria isolated were resistant to 500 mg/litre of copper Only five strains of Xanthomonas sp out of the 306 strains tested were resistant to copper; none were resistant to streptomycin