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We investigated host-induced changes of plasmid profile in two laboratory subcultured races of Xanthomonas axonopodis pv. malvacearum (Xam). Laboratory subcultured isolates contained fewer plasmids (i.e. two plasmids of size 60 and 40 kb) presumably due to loss or undetectable low copy number during subculturing. When these isolates were grown in the presence of leaf extract and intercellular fluid obtained from cotton differentials, the number of plasmids increased and the plasmid profile resembled those of the natural isolates. Based on known facts about genome rearrangement, we speculate this as an adaptation strategy for Xam to increase copy number of genes involved in pathogen aggressiveness which are otherwise present as single copy in bacterial chromosome and this possibly occurred by induction from host elicitors present in leaf extracts.
Key words: Xanthomonas axonopodis pv. malvacearum, plasmid profile, leaf extract, intercellular fluid.