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ABSTRACT
Cazorla, F. M., Arrebola, E., Sesma, A., Perez-Garcia, A., Codina, J. C., Murillo, J., and de Vicente, A. 2002. Copper resistance in Pseudomonas syringae strains isolated from mango is encoded mainly by plasmids. Phytopathology 92:909-916.
Bacterial apical necrosis of mango, elicited by Pseudomonas syringae pv. syringae, limits fruit production in southern Spain and Portugal. Examination of a collection of R 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 copperresistant 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 copperresistant 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.
Native to southern Asia, mango (Mangifera indica L.) is one of the most important fruit crops in the world. During the last 15 years, there has been a huge increase in mango production as markets have developed in Europe and North America (22). In Europe, most of the mango production is located in southern Spain and Portugal, where it has expanded steadily during the last 10 years. However, the commercial viability of this crop has been threatened by the frequent occurrence of bacterial apical necrosis, a newly reported disease of mango, which is caused by the phytopathogenic bacterium Pseudomonas syringae pv. syringae (6,8). Symptoms include necrosis of flower buds, leaves, stems, and flower panicles; it causes severe economic losses due to the decrease in fruit set.
Growers in Spain and Portugal make extensive use of registered copper compounds, mostly Bordeaux mixture, to control bacterial apical necrosis (8). In the last few years,...