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Comparison of Three Serodiagnostic Assays for Detection of Corynebacterium sepedonicum. S. A. Slack, Assistant professor, Department of Plant Pathology, University of Wisconsin Madison, WI 53706; A. Kelman(2), and J. B. Perry(3). (2)(3)Professor, and graduate student, respectively, Department of Plant Pathology, University of Wisconsin Madison, WI 53706. Phytopathology 69:186-189. Accepted for publication 21 August 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-186.

The sensitivity and specificity of an antiserum prepared against glutaraldehyde-fixed cells of Corynebacterium sepedonicum were evaluated in agglutination (AG), Ouchterlony double diffusion (DD), and indirect fluorescent antibody stain (IFAS) tests. Test sensitivity was about 2 × 10⁷ cells/ml for AG and DD, and 10¹–10² cells/ml for IFAS. A cell concentration of 10² cells/ml also could be detected by the Gram stain procedure. The ring rot bacterium was detected in stem smears from infected eggplant, potato, and tomato plants by DD and IFAS, and in infected potato tubers by AG, DD, and IFAS. Eighteen cultures of C. sepedonicum from diverse geographic origins in North America gave positive reactions with the antiserum. Cross-reactivity was observed by AG but not by DD or IFAS in comparisons with five other species of phytopathogenic corynebacteria that do not attack potato. The AG, DD, and IFAS tests with strains of Erwinia carotovora var. atroseptica, E. carotovora var. carotovora, Pseudomonas solanacearum, Bacillus spp., and Clostridium spp. were negative. Sensitivity and specificity data indicate that serodiagnostic procedures, particularly IFAS, are valuable for ring rot diagnosis.