Development of race-specific molecular marker for Xanthomonas campestris pv. campestris race 3, the causal agent of black rot of crucifers

Abstract

Race-specific molecular markers were established to distinguish Xanthomonas campestris pv. campestris (Xcc) race 3, the causal agent of black rot disease of crucifers. The available genome sequences of Xcc races were aligned and identified three DNA fragments specific to Xcc race 3. The identified race-specific DNA fragments namely XccR3-49, XccR3-52, and XccR3-55 were used for designing the race-specific primers to detect and identify Xcc race 3. The specificity of race-specific primers was tested against the genomic DNA extracted from Xcc (races 1–7), Xcc strains, Xc pathovars, and other bacterial species. XccR3-49, a specific sequence characterized amplified region (SCAR) primer set, gave a single band with 867 bp length for Xcc race 3 only. The remaining two markers XccR3-52 and XccR3-55 showed polymorphic amplification with amplicon sizes of 1889 and 2109 bp for Xcc race 3, respectively. Additionally, the SCAR primer set detected Xcc race 3 rapidly and efficiently in artificially infected cabbage leaves with bio-PCR. This result showed that the newly developed race-specific markers can successfully and efficiently detect and identify Xcc race 3 from Xanthomonas campestris pv. campestris races, Xanthomonas species/pathovars, as well as other plant pathogenic bacteria (Pseudomonas syringae pv. maculicola and Erwinia carotovora subsp. carotovora). Up to now, this is the first report describing the race-specific marker for the detection of Xcc race 3.