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Rapid Magnetic Microsphere Enzyme Immunoassay for Potato Virus X and Potato Leafroll Virus. Ernest E. Banttari, Professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108; David L. Clapper(2), Sheau-Ping Hu(3), Kristin M. Daws(4), and S. M. Paul Khurana(5). (2)(3)(4)Manager of biological research, biochemist, and biochemist, respectively, Bio-Metric Systems, Inc., 9924 West Seventy-Fourth Street, Eden Prairie, MN 55344; (5)Virologist, Division of Plant Pathology, Central Potato Research Institute, Shimla, India. Phytopathology 81:1039-1042. Accepted for publication 30 April 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-1039.

A magnetic microsphere enzyme-linked immunoassay was developed for detection of potato virus X (PVX) and potato leafroll virus (PLRV) in potatoes. Analyte, microspheres with covalently coupled antibody and antibody-enzyme conjugate, were mixed, incubated together for 10 min, magnetically separated from sap, and washed with buffer three times; finally, substrates containing a 5-bromo-4-chloro-3-indoyl phosphate/nitro blue tetrazolium or p-nitrophenyl phosphate were added. Color development (A562) or (A405) occurred in positive samples within 1520 min. Detection sensitivity for PVX was 13 ng of purified virus diluted into buffer or healthy leaf sap or PVX-infected potato sap diluted 1,000 in healthy potato sap. Detection sensitivity for PLRV was ?10 ng of purified virus diluted into healthy sap or PLRV-infected sap diluted 1,000 in healthy potato sap. This assay can be completed within 3045 min and provides assay sensitivities comparable to double antibody sandwich enzyme-linked immunosorbent assays on polystyrene or nitrocellulose solid phase carriers for these viruses.