First report of Potato mop-top virus infecting potatoes in Alberta

© 2016, American Phytopathological Society. All rights reserved. Potato mop-top virus (PMTV) is a member of the genus Pomovirus and has a single-stranded positive-sense RNA genome divided into three segments. PMTV is transmitted by the soilborne powdery scab pathogen, Spongospora subterranea (Wallroth) Lagerheim, which is widespread and occurs in most major potato growing areas. Ten tubers of potato (Solanum tuberosum L.) cv. Russet Burbank grown in southern Alberta that exhibited internal brown spots and arcs typical of infection by PMTV or Tobacco rattle virus (TRV) were collected in June 2016 from commercial potato storage. Tuber tissue exhibiting symptoms ranging from a few brown spots to several concentric arcs were sampled and tested by reverse transcription (RT) followed by PCR with primers specific for TRV (Kawchuk et al. 1997) or PMTV (Crosslin 2011). Total RNA from the tubers was isolated using the Plant/Fungi Total RNA Purification Kit (Norgen Biotek Corp., Thorold, ON) and cDNA was prepared with the single tube cDNA assay Superscript III One-Step RT-PCR(Life Technologies, Ottawa, ON) and high fidelity Platinum Taq DNA Polymerase (Fisher Scientific, Ottawa, ON). Symptomless tubers from the same storage were also examined. Cloned amplified DNA was sequenced in forward and reverse directions at least twice. PMTV and TRV were detected in tubers expressing necrotic symptoms, producing amplified products of the expected 416 and 461 bp sizes, respectively. Neither TRV or PMTV were detected in symptomless tubers. Tubers with symptoms were also positive for PMTV by DAS-ELISA and an immunocapture RT-PCR (Kalischuk et al. 2013) using commercially available polyclonal antisera (Bioreba AG, Switzerland), while symptomless tubers were negative for PMTV. All potato tubers were negative for Potato virus Y and Potato leaf roll virus in replicated ELISAs (Agdia, Elkhart, IN). The 416-bp amplicon obtained with the PMTV RT-PCR primers was cloned and sequenced. Sequence was submitted to GenBank (accession no. KX443693) and BLAST analysis showed an identical match to the coat protein gene on RNA3 of PMTV isolates from Europe (KT923158, LN614487, and AM503616). These results confirm that PMTV is present in southern Alberta. Reports published recently indicate PMTV has also been detected in surrounding states Idaho, Washington, and Oregon (Crosslin 2011, Kaur et al. 2016, Whitworth and Crosslin 2013). Detection of PMTV in Alberta indicates the pathogen is spreading to new areas and producers, processors, and regulatory agencies need to monitor the movement and prevalence of this potentially devastating virus in Canada to minimize disease losses.