First, second, fourth, fifth, and seventh authors: Departamento de Microbiología, Facultad de Ciencias, Universidad de Málaga, 29071 Málaga, Spain; and third and sixth authors: Instituto de Agrobiotecnología y Recursos Naturales, CSIC-UPNA and Laboratorio de Patología Vegetal, Escuela Técnica Superior de Ingenieros Agrónomos, Universidad Pública de Navarra, 31006 Pamplona, Spain
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Accepted for publication 4 April 2002.
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.
© 2002 The American Phytopathological Society