Copper resistance in Pseudomonas syringae strains isolated from mango is encoded mainly by plasmids.
Cazorla F. M., Arrebola E., Sesma A., Pérez-García A., Codina J. C., Murillo J., Vicente A. de
Author Affiliation: Departamento de Microbiología, Facultad de Ciencias, Universidad de Málaga, 29071 Málaga, Spain.
Phytopathology 92 : 909-916
Abstract : Bacterial apical necrosis of mango, elicited by Pseudomonas syringae pv. syringae, limits fruit production in southern Spain and Portugal. Examination of a collection of P. syringae pv. syringae isolates for copper resistance showed that 59% were resistant to cupric sulfate. The survey of a mango orchard revealed an increase in frequencies of copper-resistant bacteria after repeated treatments with Bordeaux mixture. These data suggest that selection of copper-resistant strains could be a major reason for control failures following management with copper bactericides. Most copper-resistant isolates harbored plasmids, although the majority of them contained a 62-kb plasmid that also was present in copper-sensitive strains. The 62-kb plasmids were differentiated by restriction enzyme analysis and hybridization to copABCD DNA. The most frequently found copper-resistant plasmid type (62.1) was transferable by conjugation. Southern blot hybridizations showed that genetic determinants partially homologous to copABCD were present in all the copper-resistant strains examined, and usually were associated with plasmids; these determinants were not detected in copper-sensitive strains. The selective pressure exerted by copper bactericide sprays on the diversity of copper resistance determinants in bacterial populations of mango is discussed.