Genetic diversity of Grapevine rupestris stem pitting-associated virus isolates from Tunisian grapevine germplasm

Grapevine rupestris stem pitting-associated virus (GRSPaV) is one of the most widespread grapevine viruses transmitted mainly by graft. GRSPaV presence was tested in 487 samples representative of the Tunisian grapevine germplasm (including autochthonous, table, wine, wild grape and rootstock genotypes) from different Tunisian regions. GRSPaV infection was detected in 51.3% of samples from different Tunisian regions, among them the table grapevine cultivars were the most commonly infected (68.7%). Genetic variability of GRSPaV isolates from wild and cultivated grapevines was assessed by sequencing the partial coat protein (CP) gene of nineteen Tunisian isolates and one Italian GRSPaV isolate from Sicily, and the partial RNA-dependent RNA polymerase (RdRp) gene of thirteen Tunisian GRSPaV isolates. According to phylogenetic analysis of CP nucleotide sequences obtained in this study and sequences retrieved from the GenBank, Tunisian isolates fell into four phylogenetic groups already described (Group I, II, III and IV) and two new phylogenetic groups (VI and VIII). Phylogenetic analysis of the partial RdRp reveals that Tunisian isolates of GRSPaV are distributed into four phylogroups. This study highlights the importance of regular monitoring of GRSPaV infections in Tunisia, with special regard to those grapevine accessions employed in conservation and selection programs. In particular, the presence of new GRSPaV genetic variants and infection of wild grapevines must be taken into account for choosing a correct control strategy.