Grapevine fleck virus (GFkV) is a positive-sense, single-stranded RNA virus with a genome size of 7,564 nucleotides (3). The virus is present in many grape-growing regions (1,2,4). GFkV is phloem-limited and graft transmissible, but a biological vector is not yet known (4). It causes latent infections in Vitis vinifera cultivars, but induces specific foliar symptoms in the indicator host, V. rupestris. While testing samples from wine grape cultivars, samples from cv. Chardonnay tested positive for GFkV in single-tube one-step reverse transcription (RT)-PCR assay using forward primer GFkV585F (5′-CTCAGCCTCCACCTTGCCCCGT-3′) and reverse primer GFkV1117R (5′-CAATTTGGCTGGGCGAGAAGTACA-3′). The forward primer is identical to nt 585 to 606 and the reverse primer is complementary to nt 1094 to 1117 in the GFkV genome (Accession No. AJ309022) and encompass a portion of the RNA-dependent RNA polymerase. The primer pair amplified a 533-nt fragment from 15 of 37 individual grapevines in the Chardonnay block. The amplicons obtained from five grapevines were cloned individually into the pCR2.1 plasmid (Invitrogen Corp., Carlsbad, CA). Three independent clones per amplicon were sequenced in both orientations. Sequences were edited and assembled using ContigExpress project in the Vector NTI Advance 11 sequence analysis software packages (Invitrogen). Pairwise comparisons of these sequences (Accession Nos. GU372367 to GU372371) with a corresponding sequence of a GFkV isolate deposited in the GenBank (Accession No. AJ309022) showed 89 to 97% identity at the nucleotide and 95 to 98% identity at the amino acid level. To further support these results, we amplified a 714-nt fragment specific to the complete coat protein (CP) gene of GFkV from three of the five isolates sequenced above using primers GFkV-6351F (5′-CTCTCCGCCTCGTCTGATGA-3′) and GFkV-7064R (5′-TCGGTTCATGACGAGGGAGT-3′). The amplicons were cloned and sequenced as described above. A comparison of these sequences (Accession Nos. GU372372 to GU372374) with the CP sequence of GFkV available in the GenBank (Accession No. AJ309022) showed 94 to 95% and 98 to 100% identity, respectively, at the nucleotide and amino acid level. ELISA with GFkV-specific antibodies (BIOREBA AG, Reinach, Switzerland) further confirmed the presence of the virus in samples that were positive in RT-PCR. ELISA results validated the data described above and confirmed the presence of GFkV in Chardonnay samples that tested positive by RT-PCR assay. Previously, GFkV was documented in grapevines in California and Missouri (2), Australia (4) and Europe (1). To our knowledge, this is the first confirmed report of the occurrence of GFkV in Washington vineyards. The results expand our current knowledge on the distribution of GFkV and help to prevent its dissemination through the supply of grapevine cuttings by ‘clean’ plant programs.
References: (1) G. P. Martelli et al. Arch Virol. 147:1847, 2002. (2) B. N. Milkus and R. N. Goodman. Am. J. Enol. Vitic. 50:133, 1999. (3) S. Sabanadzovic et al. J. Gen. Virol 82:2009, 2001. (4) B. J. Shi et al. Ann. Appl. Biol. 142:349, 2003.
