Abstract: This invention provides methods and reagents for screening plants, particularly geraniums, for infections with bacterial pathogens. Specifically, the invention provides nucleic acid amplification and detection methods for specifically detecting a certain pathovar of a bacterial infectious agent in geraniums. The invention provides a nucleic acid hybridization probe that is specific for Xanthomonas campestris pathovar pelargonii, and paired sets of oligonucleotide primers for polymerase chain reaction-catalyzed amplification of DNA fragments comprising the nucleic acid sequences of the invention specific for Xanthomonas campestris pathovar pelargonii template DNA. The invention also provides PCR-based methods for detecting Xanthomonas campestris pathovar pelargonii DNA, and in particular for distinguishing pathovar DNA from the DNA of the host infected plant. Methods for producing detectably-labeled hybridization probes using PCR are also provided.