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Development of an Immunosorbent Assay for Seedborne Erwinia stewartii in Corn Seeds. G. L. Lamka, Graduate assistant, Department of Plant Pathology, Iowa State University, Ames 50011, Present address: Plant Science Research, Inc., P.O. Box 337, Huxley, IA 50124; J. H. Hill, D. C. McGee, and E. J. Braun. Professor, professor, and associate professor, respectively, Department of Plant Pathology, Iowa State University, Ames 50011. Phytopathology 81:839-846. Accepted for publication 25 January 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-839.

Specificity of polyclonal and monoclonal antibodies generated to Erwinia stewartii was determined by testing 167 bacterial strains in enzyme-linked immunosorbent assay (ELISA). Of these, the antibodies were positive to all 43 E. stewartii strains tested. Reaction of the monoclonal antibody to all other bacterial strains was negative. However, the polyclonal antibodies reacted with seven of 105 nonpathogenic bacteria from corn plants and seeds determined not to be virulent E. stewartii. A double-sandwich ELISA that used the polyclonal and monoclonal antibodies was developed to detect E. stewartii in ground corn-seed samples. A comparison of four ELISA procedures to detect E. stewartii in pure culture and mixed with corn-seed tissue revealed that the most appropriate procedure was a double-sandwich ELISA using polyclonal antibodies for capture and monoclonal antibodies for detection. The assay detected E. stewartii antigen in seeds from plants inoculated with a rifampicin and nalidixic acid tolerant strain of E. stewartii but not in seeds from uninoculated plants. The presence of viable E. stewartii in seeds from inoculated plants was confirmed by culture. Analyses of 400 single seeds showed an absolute positive correlation between recovery of bacteria and ELISA response in eight seeds. E. stewartii was recovered from 10 other seeds that had a negative ELISA response. Recovered bacterial populations in nine of these 10 seeds were below the threshold of detection by ELISA.