Abstract
Potato virus Y (PVY), potato mop-top virus (PMTV), potato virus S (PVS), and tobacco rattle virus (TRV) can be difficult to identify based on visual foliar symptoms. Using tuber samples collected from seven locations and 12 cultivars during 2017-2019, we developed a molecular assay using customized Whatman Flinders Technology Associates Plantsaver® Cards (FTA cards) and a reverse-transcription polymerase chain reaction (RT-PCR) for efficient sample collection and nucleic acid extraction. PMTV and PVY were detected more frequently on the stem-end, TRV on the rose-end, and PVS was evenly detected across stem-end to rose-end axis of the tubers. Differences were seen in virus species localization within a tuber, thereby a composite of samples taken from multiple locations on a tuber improved virus detection. Regardless of sampling location on the tuber, tissue excised from surface to 0.5 cm deep provided the best detection for all four viruses. For PVY, PMTV, and TRV, the proportion of tubers with virus detected from field samples was highest at 100, 150, and 175 days after harvest, respectively. However, the probability of detecting PMTV and PVY 25 days after harvest was not different than the probability of detection at their peak detection times after harvest. The probability of TRV detection was lower at 25 days after harvest than at 175 days after harvest (P < 0.05).