Detection of Xanthomonas campestris pv. pelargonii in geranium and greenhouse nutrient solution by serological and PCR techniques

Specificity of a new monoclonal antibody, 2H5, to Xanthomonas campestris pv. pelargonii, causal agent of geranium bacterial blight, was determined by enzyme-linked immunosorbent assay (ELISA) and immunofluorescence tests on 14 strains of X. c. pelargonii, 12 strains of other X. campestris pathovars, 3 strains of other Xanthomonas spp., 3 strains of other plant pathogens, and 43 saprophytic bacteria isolated from geranium. X. c. pelargonii was detected in tissue from symptomatic and asymptomatic geraniums sampled from commercial growers, and artificially inoculated plants, by monoclonal antibody-based tests. The intensity of response in ELISA was only moderately correlated (r = 0.56) with symptom severity, while symptom severity was not correlated (r = 0.16) with the number of fluorescing cells in immunofluorescence. The bimodal frequency distribution of ELISA and immunofluorescence results served to validate arbitrarily chosen positive/negative threshold values. Most positive ELISA and immunofluorescence test results were confirmed by the polymerase chain reaction (PCR) using published primers (Manulis et al., 1994. Appl. Environ. Microbiol 60, 4094-4099). In contrast to plant tissue, the bacterium was detected in greenhouse nutrient solution with greater sensitivity by immunofluorescence and PCR than by ELISA. Sensitivity of detection was enhanced 100-fold by concentration of the bacteria by centrifugation.