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An Enzyme-Linked Immunosorbent Blocking Assay for Comparing Closely Related Virus Isolates. Charles A. Powell, Plant pathologist, Pennsylvania Department of Agriculture, 2301 N. Cameron St., Harrisburg, PA 17110; Mike A. Derr, plant industry technician, Pennsylvania Department of Agriculture, 2301 N. Cameron St., Harrisburg, PA 17110. Phytopathology 73:660-664. Accepted for publication 15 November 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-660.

Ouchterlony double diffusion comparison of tomato ringspot virus (TmRSV) isolated from apple (A), blueberry (B), geranium (G), and cymbidium orchid (O) showed that all four isolates had at least one antigenic determinant in common, and A- and B-TmRSV had at least one additional antigenic determinant in common, which was not shared by TmRSV-G or -O. An enzyme-linked immunosorbent blocking assay (EIBA), which compares the relative abilities of excess unlabeled heterologous and homologous antigen to block the binding of enzyme-labeled antigen to its immobilized homologous IgG, was developed to more closely scrutinize the serological relationships. EIBA revealed additional antigenic differences among the four TmRSV isolates not detected by double diffusion tests.