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Neutralization of Infectivity of Potato Yellow Dwarf Virus and Wound Tumor Virus Assayed on Vector-Cell Monolayers. Ho- Yuan Liu, Research Associate, Department of Genetics and Development, University of Illinois, Urbana, IL 61801, Present address of senior author: Research Associate, School of Basic Medical Sciences, University of Illinois, Urbana, IL 61801; L. M. Black, Professor Emeritus, Department of Genetics and Development, University of Illinois, Urbana, IL 61801. Phytopathology 68:1243-1248. Accepted for publication 10 February 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1243.

At antiserum dilutions greater than 102 specific neutralization reactions could be expressed as a straight line relationship between the logarithm of the number of infected cells in vector cell monolayers and the logarithm of the serum concentration. Neutralization could be detected at up to a hundredfold greater antiserum dilution than the precipitin interface reaction against virus. At serum dilutions between 102.5 and 10 2.0, a marked increase in the slope of the neutralization curve was produced by antiserum but not by pre-immune control serum; the latter had no significant neutralizing activity at any dilution tested. The slope of the straight line was the same for the two potato yellow dwarf virus (PYDV) systems but different for the wound tumor virus (WTV) system. Tests revealed no cross neutralizations between antiserum to sowthistle yellow vein virus (SYVV) and PYDV or between antiserum to rice dwarf virus (RDV) and WTV. Cross neutralization occurred between two field forms of PYDV but cross neutralization was stronger in one direction than in the other. Heterologous immunofluorescent staining was less intense than control homologous staining and fluorescent antibodies to the two field forms of potato yellow dwarf virus stained about 1% as many infected cells heterologously as homologously. Cross absorption of conjugated antiserum with heterologous virus eliminated cross-reactive but not homologous staining.