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A new species of the genus Potyvirus infecting potatoes, with the proposed name Potato yellow blotch virus (PYBV), was discovered in a breeding line 99m‐022‐026 in Scotland. The infected plants show isolated yellow blotches on the leaves. The genome of PYBV contains a large open reading frame encoding a single polyprotein of 3054 amino acids. Sequence analysis shows that PYBV is closely related to Potato virus A (PVA), with an overall 72% identity at the nucleotide level for the whole genome. The least conserved P1 protease gene shares only 50% nucleotide identity with PVA. The host range of PYBV was comparable to PVA on solanaceaous and non‐solanaceous indicator plant species with the exception of Solanum demissum A and Y. Different symptoms were also observed for PYBV and PVA in Nicotiana benthamiana, Nicotiana hesperis and Nicotiana occidentalis P1. The susceptibility of potato (Solanum tuberosum) cultivars to PYBV and PVA was similar. In over 5 years of investigation, PYBV has not been found in commercial seed and ware potato crops in Scotland. [ABSTRACT FROM AUTHOR]

In an attempt to resolve whether two putative carlaviruses, potato rough dwarf virus (PRDV) and potato virus P (PVP), reported infecting potato in Argentina and Brazil, respectively, are the same virus in the genus Carlavirus, they were characterized using nucleotide sequence analysis, serology and bioassay. For PRDV and PVP, sequences of 2016 and 1492 bp, respectively, were obtained. Similarity searches of coat-protein amino acid sequences and the presence of the nucleic-acid-binding protein exhibiting the characteristic motif C-X2-C-X11-C-X4-C, highly conserved in carlaviruses, showed PRDV and PVP to be members of the genus Carlavirus. Further analysis showed that they were the same virus species since the full coat-protein sequence, translated from the nucleotide sequence, exceeded the 84% minimum identity required for members of the same species within the genus Carlavirus, at 90·8% identity in an ungapped alignment of 304 amino acids. Moreover, the viruses could not be distinguished using polyclonal antibodies raised to PRDV and PVP in ELISA. They could, however, be distinguished using an anti-PVP monoclonal antibody, which did not react to PRDV, and by differences in the susceptibility of plant species and potato cultivars to infection and/or symptom expression following mechanical inoculation. Host plants Datura metel, Nicandra physalodes and Nicotiana edwardsonii were reliably infected systemically with PVP, but not with PRDV. Although all potato cultivars tested were infected, there were marked differences between cultivars in the symptoms produced. The cultivars Ditta and King Edward showed symptoms (including stunting and mottle) when infected with PRDV, but not when infected with PVP. Based on the results, it is proposed that PRDV is a strain of PVP within the genus Carlavirus. For detection of the viruses in postentry quarantine, it is recommended that PRDV or PVP polyclonal antibodies are used, together with inoculation to Nicotiana occidentalis N. megalosiphon-P1. For differentiation of PRDV and PVP, the PVP monoclonal antibody may be used together with inoculation to D. metel and N. physalodes (systemic infection with PVP but not PRDV, determined using ELISA). [ABSTRACT FROM AUTHOR]