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Isolation and Partial Nucleic Acid Characterization of a New Isolate of Potato virus V with Distinct Biological and Serological Properties

In vitro cultures of potato (Solanum tuberosum cv. Papa Amarillo) were imported into the United States and were subjected to routine pathogen screening for newly introduced varieties. These cultures indexed positive for several of the six viruses tested and thus were treated using standard methods for eliminating viruses in in vitro cultures. Although the therapy apparently freed the potato of the tested viruses, some of the cultures continued to exhibit mosaic symptoms when planted in the greenhouse. When examined by electron microscopy, these plants contained flexuous rods. Tested samples did not index positive with any potato virus-specific polyclonal antisera but reacted with the “universal” potyvirus monoclonal antibody. These results indicated that these samples were likely infected with an as yet undescribed potyvirus. Further investigation indicated that this virus is a new strain of Potato virus V (PVV) that is serologically distinct from the common strain. This is the first description of a distinct strain of PVV. This particular strain has diverged sufficiently from other isolates of PVV to no longer be detectable by some commonly used antisera, and therefore is a concern for the future restriction of PVV spread into regions of the world where it is not currently present.