Canadian Food Inspection Agency, Centre for Animal and Plant Health, 93 Mount Edward Road, Charlottetown, PEI, Canada, C1A 5T1
Potato mop-top virus (PMTV) was detected in potatoes grown in the United States and Canada during surveillance testing by a reverse transcription-polymerase chain reaction (RT-PCR) targeting the coat protein gene in RNA3. Out of 3,221 lots of seed and ware potatoes that were tested, 4.3% were positive for PMTV. The reliability of the survey results was confirmed by reextraction of selected samples and additional RT-PCR tests using two primer sets targeting gene segments in RNA2 and RNA3. Amplicons generated from RNA2 and RNA3 were identified by analysis of fragment length polymorphisms after digestion with BamHI and HindIII, respectively. PMTV was further identified by enzyme-linked immunosorbent assay, bioassay on Nicotiana debneyi, and transmission electron microscopy. Sequencing of a portion of the coat protein gene revealed near 100% identity among isolates from the United States and Canada and >97% homology of the North American isolates with European isolates.