First Report of Nasturtium as a Natural Host of Cherry leaf roll virus on Amsterdam Island

Distribution of Barley yellow dwarf virus-PAV in the Sub-Antarctic Kerguelen Islands and Characterization of Two New Luteovirus Species

A systematic search for viral infection was performed in the isolated Kerguelen Islands, using a range of polyvalent genus-specific PCR assays. Barley yellow dwarf virus (BYDV) was detected in both introduced and native grasses such as Poa cookii. The geographical distribution of BYDV and its prevalence in P. cookii were analyzed using samples collected from various sites of the archipelago. We estimate the average prevalence of BYDV to be 24.9% in P. cookii, with significant variability between sites. BYDV genetic diversity was assessed using sequence information from two genomic regions: the P3 open reading frame (ORF) (encoding the coat protein) and the hypervariable P6 ORF region. The phylogenetic analysis in the P3 region showed that BYDV sequences segregate into three major lineages, the most frequent of which (Ker-I cluster) showed close homology with BYDV-PAV-I isolates and had very low intra-lineage diversity (0.6%). A similarly low diversity was also recorded in the hypervariable P6 region, suggesting that Ker-I isolates derive from the recent introduction of BYDV-PAV-I. Divergence time estimation suggests that BYDV-PAV-I was likely introduced in the Kerguelen environment at the same time frame as its aphid vector, Rhopalosiphum padi, whose distribution shows good overlap with that of BYDV-Ker-I. The two other lineages show more than 22% amino acid divergence in the P3 region with other known species in the BYDV species complex, indicating that they represent distinct BYDV species. Using species-specific amplification primers, the distribution of these novel species was analyzed. The high prevalence of BYDV on native Poaceae and the presence of the vector R. padi, raises the question of its impact on the vulnerable plant communities of this remote ecosystem.

Complete nucleotide sequence of Cherry leaf roll virus (CLRV), a subgroup C nepovirus

The complete nucleotide sequence of both genomic (+)ss RNAs of a rhubarb isolate of Cherry leaf roll virus (CLRV) was determined. The larger RNA1 is 7918 nucleotides and the shorter RNA2 6360 nucleotides in size, each genome component comprising a single open reading frame (ORF). The RNA1-encoded polyprotein (P1) is 2112 amino acids long (235.6 kDa) containing domains characteristic for a proteinase-cofactor (PCo), nucleotide-binding helicase (Hel), genome-linked protein (VPg), proteinase (Pro), and an RNA-dependent RNA polymerase (Pol). The RNA2-encoded polyprotein (P2) has a molecular mass of 174.9 kDa (1589 aa) encoding the putative movement protein (MP) and the coat protein (CP) of CLRV. The genome region upstream of the MP has a coding capacity of 77 kDa, however processing of P2 by the putative virus-encoded proteinase and protein-function encoded by this region is unknown. Furthermore, it could be demonstrated that the 5'-termini including the N-terminal region (208 aa) of P1 and P2 of the rhubarb isolate of CLRV are nearly identical among the two genome segments. The taxonomic position of CLRV as member of the genus Nepovirus was confirmed by phylogenetic analyses employing the amino acid sequences of the conserved Pro-Pol region of RNA1, the complete P2, and the CP. However, clustering of Nepovirus-species according to allocated subgroups was inconsistent and depended on the compared genome fragment.