Use of Serology to Detect Xanthomonas campestris pv. pelargonii in Aqueous Extracts of Geranium Plants. J. E. Tuinier, Former Graduate Assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. C. T. Stephens, Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Plant Dis. 73:875-878. Accepted for publication 25 April 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0875.

A direct double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) proved superior to latex bead aggutination (LBA) for rapid detection of Xanthomonas campestris pv. pelargonii in aqueous extracts of geranium plants. The antisera, obtained from rabbits injected with live cells of X. c. pv. pelargonii, did not react with strains of Erwinia, Pseudomonas, Clavibacter, or Agrobacterium in either the DAS-ELISA or the LBA tests. The antiserum reacted strongly with two strains each of X. c. pv. campestris and pv. vesicatoria, but higher values were obtained with strains of pv. pelargonii. With the DAS-ELISA test, cells of X. c. pv. pelargonii were detected in aqueous extracts of plants that had been inoculated and incubated and either developed symptoms or were symptomless but infected. In contrast, none of the extracts of noninoculated plants were positive in the DAS-ELISA. The assays were completed within 24 hr, as compared with the 4–5 days needed for isolation, culture, identification, and inoculation. False-positive or false-negative results were recorded frequently in the LBA assay of the same extracts. Only 56% of the extracts of diseased geranium plants appeared positive.