Sequence diversity, population genetics and potential recombination events in grapevine rupestris stem...

Grapevine rupestris stem pitting-associated virus (GRSPaV; genus Foveavirus, family Flexiviridae) is present in many grape-growing regions of the world. A total of 84 full-length coat protein (CP) sequences and 57 sequences representing the helicase-encoding region (HR) of the RNA-dependent RNA polymerase were obtained from wine grape cultivars grown in the Pacific North-West (PNW) of the United States and their molecular diversity was compared with corresponding sequences previously reported from other grape-growing regions. In pairwise comparisons, the CP sequences from PNW isolates showed identities between 80 and 100% at the nucleotide level and the HR sequences showed identities between 79 and 100%. A global phylogenetic analysis of the CP and HR sequences revealed segregation of GRSPaV isolates into four major lineages with isolates from PNW distributed in all four lineages, indicating a lack of clustering by geographical origin. Scion cultivars grafted onto rootstock were found to contain mixtures of more genetic variants belonging to different lineages than own-rooted cultivars. Assessment of population genetic parameters found that the CP was more variable than the HR region. The discordant gene phylogenies obtained for some CP and HR sequences and the identification of potential recombination events involving parents from different lineages provided strong evolutionary evidence for genetic diversity among GRSPaV isolates. These results underscore the highly variable nature of the virus with implications for grapevine health status and distribution of virus-tested planting materials. This study also contributes to an increased understanding of molecular population genetics of viruses infecting deciduous woody perennials.