Occurrence of grapevine virus A in wild grapevines (Vitis vinifera subsp. sylvestris) in Tunisia

Wild grapevine (Vitis vinifera subsp. sylvestris) populations exist in the northern mountain forests of Tunisia (Harbi Ben Slimane et al., 2010). These populations can be natural reservoirs of pathogens including viruses (Pacifico et al., 2016). Grapevine virus A (GVA) is the type member of the genus Vitivirus in the family Betaflexiviridae. GVA has a worldwide distribution, is associated with Kober stem grooving and Shiraz diseases (Minafra et al., 2017), and is widely distributed in Tunisian vineyards (Mahfoudhi et al., 1998). To study the presence of this virus in wild grapevines, a survey was carried out in the mountain forests of northern Tunisia in spring and autumn of 2015. Dormant canes from 84 accessions (male and female specimens) were collected and tested for the presence of GVA by RT-PCR using specific primers (MacKenzie, 1997) to amplify a 236 bp fragment of the coat protein gene. Results showed that 13% (11 of 84) of the tested samples were infected by GVA. To confirm the presence of GVA in wild Tunisian grapevines, RT-PCR amplicons from three positive accessions were sequenced and sequences were compared with those from GenBank. The nucleotide sequence identity of Tunisian GVA isolates VS15 (LT906663), VS16 (LT906664) and VS178 (LT906665) ranged from 92 to 96% among themselves and from 89 to 93% with other isolates for which information is available in GenBank. To our knowledge, this is the first report of GVA in wild grapevines in Tunisia.