• aetiology
• grapevine
• GRSPaV
• molecular characterization
• vein necrosis

Vein necrosis (VN) is a virus-like disease of grapevine that is latent in V. vinifera and in most of rootstock and hybrids, with the only exception of rootstock 110 Richter (V. berlandieri x V. rupestris). Despite its ubiquitous presence in many grape growing regions, its economic impact on production is still largely unknown, because of its latency in V. vinifera. Though the causal agent of VN has not been identified, as the disease is able to be transmitted by grafting, VN is then considered a virus-like disease. Recent studies suggested a correlation between VN and the virus Grapevine rupestris stem pitting-associated virus (GRSPaV).
In this research, the presence and molecular variability of GRSPaV in grapevine accessions from Tuscany and California was studied through RT-PCR and sequence analyses. RT-PCR analyses with group-specific primer sets distinguished three molecular groups of GRSPaV variants. All of the three groups were detected both in Tuscan and Californian grapevine accessions.
Amplification, cloning and sequencing of two distinct viral genomic regions were carried out in order to obtain a finer molecular characterization of GRSPaV isolates. Depending on the genomic region analyzed, five (ORF5) to six (ORF1) phylogenetic groups of virus variants were observed. Notably, the sixth phylogenetic group identified according to sequence analysis of a 299 nucleotides fragment of ORF1 comprises only GRSPaV variants derived from Tuscan grapevine accessions, that show low nucleotide identity with any other GRSPaV sequence deposited in GenBank. This could represent a new and possibly yet unknown phylogroup of GRSPaV variants, that has named “group 5”.
Linking the results of GRSPaV molecular characterization with those of VN biological indexing previously conducted on the accessions object of the study, a strong correlation emerged between VN positive plants and infections by GRSPaV variants belonging to phylogenetic groups 2a and 2b.
In order to further assess this correlation, a biological indexing trial was performed for 37 grapevine accessions from Italy (Tuscany and Apulia), USA, Portugal and Japan. Results obtained confirmed the hypothesis that only phylogenetic groups 2a and 2b of the virus are able to induce VN symptoms on indicator host 110 Richter.
These findings show evidence of a different role of GRSPaV variants in VN determinism; only phylogenetic groups 2a and 2b appear to be able to induce symptoms of VN. This could suggest the possibility to diagnose VN by RT-PCR assays with group-specific primers, representing a much faster, cheaper and more simple way to monitor the diffusion and incidence of this disease.