First Report of Grapevine redglobe virus (GRGV) in Grapevine in France.

The isometric virus Grapevine redglobe virus (GRGV), was first described on grapevine cv. Red Globe in southern Italy in 2000 (3) and later in Greece and California. GRGV belongs to the genus Maculavirus in the family Tymoviridae. These viruses are thought to be disseminated through propagation and grafting, as no vectors or seed transmission are known to date. A partial sequence (2,006 nucleotides [nt]) encompassing the 3' end of the replicase, the coat protein, and P17 genes, was obtained in 2003 (1). GRGV infections are apparently symptomless (2). In 2014, GRGV was identified by Illumina sequencing of total RNAs extracted from a Vitis vinifera cv. Cabernet franc (CF) vine grafted onto Gravesac in a vineyard of the Bordeaux region in France. This Cabernet franc plant displayed fanleaf-like degeneration symptoms associated with Tomato black ring virus (TBRV) infection. It had been collected in 2010 and maintained since in a greenhouse. The partial contigs assembled from the Illumina reads (552 and 430 nt, both in the putative replicase gene, KM491303 and KM491304) showed 85.9 and 86.3% nt identity with the partial sequence of a GRGV Italian isolate (AF521577), respectively. Total RNA extracts from leaves of 18 plants of cv. Cabernet franc from the same plot, collected in 2014, were analyzed by RT-PCR using specific primers RG-CF-F1 (5'-GAATTCGCTGTCGGCCACTC-3') and RG-CF-R1 (5'-AGTGAGAGGAGAGATTCCATC-3') designed on the basis of the alignment of the partial sequences of GRGV-CF and the Italian isolate (AF521577). Fifteen (83%) of the plants gave strong positive amplification for GRGV. Given the mixed viral infection status of these vines, it was not possible to associate a specific symptomatology with the presence of GRGV. Two RT-PCR amplicons were directly sequenced and showed 91.5 and 91.7% identities, respectively, with the reference GRGV-CF sequence. To our knowledge, this is the first report of GRGV in France. Further studies will be necessary to determine the prevalence of GRGV in the French vineyards and varieties, including rootstocks, and its possible threat to the grapevine industry. Studies are also needed to assess the pathogenicity of GRGV. Similarly to its close relative, Grapevine fleck virus, does it induce latent or semi-latent infections in Vitis vinifera and rootstock hybrids, influencing vigor, rooting ability, and graft compatibility? References: (1) N. Abou Ghanem-Sabanadzovic et al. Virus Genes 27:11, 2003. (2) G. P. Martelli et al. Arch. Virol. 147:1847, 2002. (3) S. Sabanadzovic et al. Arch. Virol. 145:553, 2000.