Nine strains belonging to 2 races of Xanthomonas campestris pv. malvacearum (Xam), synonym, Xanthomonas axonopodis pv. malvacearum (Xam) were screened for their plasmid content. One strain belonging to race 4, which has been attenuated as a mutant from race 18 was less virulent than race 18, even though it possessed the same plasmids as race 18 strains. Five groups could be distinguished based on their plasmid profiles. The first group includes the race and 4 strain and 4 isolates of race 18 from Nicaragua that were isolated in 1986. The other 4 isolates of races 18, isolated from Nicaragua in 1986; the USA in 1986; and Sudan in 1991 were separated into 4 distinct groups according to their plasmid profile. The attenuated strain of race 4 was more sensitive to antibiotics and heavy metal ions than the race 18 strains. There was no indication that these plasmids play a distinct role in virulence of these Xam strains.
Key words: Plasmid, Xanthomonas, antibiotics, heavy metals
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