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Repetitive extragenic palindromic polymerase chain reaction (rep-PCR), sequencing of the 16S−23S rDNA internal transcribed spacer (ITS), biochemical and physiological tests, the Biolog microplate system, polyacrylamide gel electrophoresis (PAGE) of whole-cell proteins, and pathogenicity tests were used to characterize variability among xanthomonads isolated from pistachio trees suffering from bacterial dieback in four regions of Australia. ITS sequencing and rep-PCR revealed two distinct genotypes among the strains. The ITS sequencing suggested that the pistachio strains were closely related to Xanthomonas translucens pathovars, in particular X. translucens pv. poae. Results of physiological and biochemical tests, as well as Biolog microplate analysis and protein profiling, confirmed the existence of two groups. Furthermore, pathogenicity and host-range studies indicated that the two groups were biologically different. There was an association between the two groups and the geographical origin of the strains. |
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