Characteristics of a PCR-Based Assay for In Planta Detection of Xanthomonas campestris pv. pelargonii

Polymerase chain reaction (PCR) amplification was carried out with a primer pair targeting a sequence in the genome of Xanthomonas campestris pv. pelargonii, the causative agent of bacterial blight in geraniums. PCR amphfication with the primer pair XcpMl/XcpM2 using total nucleic add preparations from 22 geographicallydiverse isolates of X. campestris pv. pelargonii generated a major 197 bp DNA product. In contrast, no major amplification products were consistently generated from !2 other pathovars of X. campestris or from 19 isolates representing 10 different plant pathogenic bacteria, including two other bacterial pathogens of geraniums, Corvnebacterium fascians and Pseudomonas cichorii. After PCR using this primer pair, between 1380 and 13 800 copies of the X. campestris pv. pelargonii bacterial DNA target as template were detected by ethidium bromide staitiing of agarose gels, and between 13.8 and 138 copies by blot hybridization to a pathovar-specific biotinylated probe. Similarly, between 630 and 6300 colonyforming units (CFU) of X. campestris pv. pelargonii could be detected after ethidium bromide staining of agarose gels, and between 63 and 630 CFU after blot hybridization. The PCR-based assay was used to identify X. campestris pv. pelargonii in diseased geraniums; whereas discrete amplification products were not obtained with healthy plants.