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The complete genome comprising three genomic RNAs of three Canadian and two Chinese isolates of Potato mop-top virus were sequenced and analysed. Two open reading frames (ORFs) were found in RNA1 of 6.1 kb, encoding a readthrough RNA-dependent RNA polymerase (RdRp). A coat protein (CP)-readthrough protein was encoded by RNA2 of 3.1 kb. Four ORFs that encoded the triple gene block proteins (TGBps) and a cysteine-rich protein were found in RNA3 (2.9 kb) of the Chinese isolate ‘Yunnan’; whereas in the remaining isolates (three Canadian isolates and the Chinese isolate ‘Guangdong’), only three ORFs encoding TGBps were observed in RNA3. A single nucleotide mutation of A2462 to G2462 abolished the start codon ‘AUG’ for the fourth putative ORF in RNA3 of these isolates. Based on phylogenetic and sequence similarity analysis of these isolates as well as those reported by others at the complete RNA sequence level, each of RNA1, RNA2 and RNA3 could be divided into at least two groups. In Canadian isolates ‘Ch9’, ‘Ch10’ and ‘Ch20’ and Chinese isolate ‘Guangdong’, all genomic RNAs belonged to group A; and in Chinese isolate ‘Yunnan’, all of its RNA belonged to group B. Interestingly, in Swedish isolate ‘Sw’, RNA1 and RNA2 belonged to group A while RNA3 belonged to group B. A duplex RT-PCR for differentiating groups A and B of RNA3 was developed and evaluated. All PMTV samples collected in Guangdong, China, and New Brunswick, Canada, possessed a RNA3 belonging to group A; whereas the samples collected in Yunnan, China, possessed a RNA3 belonging to group B.

Post-harvest screening of potato ‘Kennebec’ revealed a Potato virus Y (PVY) incidence of 15.8%, a rate that is unusually high for a cultivar possessing a high level of field resistance to the virus. Randomly selected tubers were planted in a field plot and the resulting plants were monitored. Approximately 16% of plants developed symptoms ranging from mild mosaic symptoms to severe necrosis/rugosity/stunting. ELISA and RT–PCR analysis revealed that infections with Potato virus S (PVS), Potato virus X (PVX) and PVY, mostly in mixed-infections, occurred commonly in 14 sampled plants. Two strains, namely the common strain (PVY°) and the recombinant tuber necrotic strain (PVYNTN) were identified in the PVY-positive plants. In general, mild mosaic was associated with infections with PVX and PVS; intermediated mosaic was associated with PVS and PVYNTN infections; whereas severe leaf deformation/necrosis/drop symptoms were associated with PVYNTN and PVX co-infections, or with PVY° and either PVS or PVX ...

Graft inoculation of potato (Solanum tuberosum) ‘Shepody’ plants with Potato virus A (PVA) results in hypersensitive resistance responses (HR) in tubers with characteristic necrosis. Increasing the number of PVA-containing scions or increasing the duration of scions on the ‘Shepody’ rootstock plants resulted in an increased number of tubers showing necrosis. Transgenic ‘Shepody’ plants with a sense or an antisense copy of PVA coat protein (CP) gene under the direction of the CaMV 35S promoter were developed. The plants were subjected to graft inoculation with PVA in the greenhouse and were monitored by detecting PVA using enzyme-linked immunosorbent assays and reverse transcriptase polymerase chain reaction during the growing season. No PVA was detected in the wild type or the antisense-CP transgenic lines. However, PVA was detected from one of the two sense-CP transgenic lines. Potato tubers from graft-inoculated plants were harvested 3 months after inoculation and were examined for necrosis. In...

Previous studies have identified a recombinant isolate group of the Potato virus Y (PVY), PVYN:O, which exhibits a PVYO serotype and a PVYN pathotype. Molecular fingerprinting indicated that the isolates possess a European (Eu)–PVYN/NTN-like P1 gene and one PVYN-PVYO recombinant joint at the HC/Pro-P3 site. In this study, the complete genomic RNA sequence of two isolates of PVYN:O was determined. The overall identities at the polyprotein level between PVYN:O and other isolates ranged from 94.1% to 97.2%. However, the identities varied from 70.9% to 100% when individual mature proteins were compared. Scanning the nucleotide sequences revealed that PVYN:O comprises a recombinant genome in which the segment of nucleotides 1 to ~2400 is from Eu-PVYN, and the remainder from PVYO. Analysis of a population of PVYN:O isolates indicated the existence of pathological variants that induced different symptoms level in tobacco plants: severe, 16.7%; intermediate, 66.7%; and mild, 16.7%. Three representative isolates w...

(1996). Nucleotide sequence and genome organization of a Canadian isolate of the common strain of potato virus Y (PVY°) Canadian Journal of Plant Pathology: Vol. 18, No. 3, pp. 209-224.