Potyvirus complexes in sweetpotato: Occurrence in Australia, serological and molecular resolution, and analysis of the sweet potato virus 2 (SPV2) component

A survey for viruses in sweetpotato revealed the presence of Sweet potato virus 2 (SPV2; synonymous to Sweet potato virus Y and Ipomoea vein mosaic virus), a tentative member of the genus Potyvirus, for the first time in Australia. The SPV2-infected sweetpotato plants were also infected with strains RC and/or C of Sweet potato feathery mottle virus (SPFMV; genus Potyvirus). Five SPV2 and SPFMV isolates from Australia were sequence-characterized at the 3'-proximal end (ca. 1.8 kb) of the genome. A simple and sensitive diagnostic procedure was devised to readily differentiate SPV2 and the two strains of SPFMV from sweetpotato plants that contained these viruses in complexes. The method involved reverse transcription with oligoT(25) primer, polymerase chain reaction using a combination of degenerate primers, and restriction analysis of the 1.8-kb amplification products with HindIII and PvuII endonucleases. The N-proximal 543 nucleotides of the SPV2 coat protein-encoding sequence of the Australian isolates and 14 other isolates from Asia, Africa, Europe, and North America were subjected to phylogenetic analysis. The Australian SPV2 isolates formed a separate clade that was closest to a clade containing two North American isolates.