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Plants of Thunberg fritillary (Fritillaria thunbergii Miq.) from Zhejiang Province, were found to be co-infected with two distinct potyviruses. One was an isolate of the recently reported Thunberg fritillary mosaic virus (TFMV; Wei et al., (2005) Arch Virol 150: 1271-1280), while the other was a distinct virus that did not react with TFMV antiserum nor with antisera to 17 other potyviruses, except for a weak reaction with antibodies produced to soybean mosaic virus (SMV) Pinellia strain. Both viruses could be transmitted mechanically to their original host but not to any of a range of commonly used indicator plants. No local lesion host was identified that would enable the viruses to be propagated independently. The complete sequences of both viruses were determined; that of the new virus (9656 nt) had the typical genome organisation and recognised sequence motifs of a potyvirus, encoding a putative polyprotein of 351 kDa. Phylogenetic analysis, sequence comparisons, and the pattern of polyprotein cleavage sites all indicated that it was a member of the Bean common mosaic virus subgroup. The most closely related species are Soybean mosaic virus and Wisteria vein mosaic virus, with 68-69% amino acid identity between their polyproteins. This is sufficiently different for the new virus to be regarded as a distinct species, which we have tentatively named Fritillary virus Y.

The host range and nucleotide sequence of shallot yellow stripe virus (SYSV) from welsh onion in Shandong province, China is described. Of the plants tested, only shallot and welsh onion became infected but most shallot plants were symptomless. The complete sequence of one isolate (10429 nt) and the 3'-terminal 3540 nts of a second isolate were determined. They had c. 90% nt identity to one another and to published (partial) sequences of SYSV. SYSV was most closely related to onion yellow dwarf virus (OYDV) and resembled it in having a much larger P3 protein than other species in the genus.

A potyvirus causing mosaic symptoms in Thunberg fritillary (Fritillaria thunbergii) was found at two sites in Zhejiang province, China. The virus was readily mechanically transmitted to its original host but not to any of 17 other widely used plant virus indicators. A polyclonal antiserum raised to purified virus particles reacted with its homologous virus but not with a range of other viruses (including 16 potyvirus species). In electron microscopy, virus particles and inclusion bodies typical of a potyvirus were seen. The complete nucleotide sequence of an isolate from Ningbo was determined. It was 9723 nt long and sequence analyses predicted the standard potyvirus organisation. The partial sequence (1664 nts at the 3'-terminus) of an isolate from Panan was also determined; the two sequences had 96.9% nt identity. In sequence comparisons and phylogenetic analyses with completely sequenced potyviruses, the new virus was most closely related to Lily mottle virus (53.0% aa identity) and Leek yellow stripe virus. The most closely related incomplete sequence in the international databases was for Lycoris mild mottle virus (72.8% nt identity in their coat proteins). These results suggest that the virus studied is a new species in the genus Potyvirus, which we have tentatively named Thunberg fritillary mosaic virus.