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First Report of Grapevine fleck virus in Idaho Grapevines

Idaho has a growing viticulture industry, with nearly 1,600 acres of wine grapes (Vitis vinifera L.). Production is largely concentrated in two locations, the Snake River valley, which includes Canyon County in the southwest, and the Clearwater River valley, primarily Nez Perce County in the northwest. Grapevine fleck virus (GFkV) belongs to the genus Maculavirus, family Tymoviridae, comprising positive-sense, single-stranded RNA viruses with ca. 7.6-kb genome (3). It is one of five non-mechanically transmitted viruses associated with the fleck disease complex and has been previously documented to occur in the neighboring state of Washington (2). Main sources of wine grape nursery material imported to Idaho reside in Washington or in California, and it is important to monitor virus status of the planting material brought to the state. However, no information was available on the occurrence and prevalence of GFkV in wine grapes in Idaho. During three growing seasons in 2009 through 2011, random grapevine samples were collected in 14 vineyards in Canyon, Elmore, Ada, and Nez Perce counties. A total of 434 samples were tested by one step RT-PCR using GFkV-specific primers, GFkVf: 5′-TGACCAGCCTGCTGTCTCTA-3′ and GFkVr: 5′-TGGACAGGGAGGTGTAGGAG-3′ designed to amplify a fragment of the GFkV capsid protein gene (1). Twenty-four samples tested positive for GFkV by RT-PCR and produced the expected 179-bp DNA fragment. These samples came from five vineyards sampled across all surveyed counties, and represented seven wine grape cultivars, including Pinot Noir, Cabernet Sauvignon, Syrah, Lemberger, Riesling, Chardonnay, Pinot Gris, and one unknown table grape cultivar. Twelve PCR products were cloned into the pGEM-T Easy plasmid vector (Promega), sequenced (numbered ID1 to 12, available upon request), and confirmed to represent fragments of the GFkV CP gene between positions 6,453 and 6,631 in the genome of GFkV isolate MT48 (GenBank Accession No. AJ309022.1). Eight of the Idaho GFkV sequences (ID2, ID3, ID7 to 11, and ID12) matched closely with other GFkV sequences from Washington State, Italy, India, and South America, showing 97 to 99% identity at the nucleotide level in pair-wise comparisons. Four GFkV sequences from Idaho (ID1 and ID4 to 6) showed only modest (90 to 92%) identity in pair-wise comparisons with GFkV sequences available in GenBank. Consequently, in phylogenetic reconstructions eight Idaho GFkV sequences clustered in the same lineage with the six GFkV sequences deposited in GenBank, and four other GFkV sequences were placed outside of this main clade. It is possible that this phylogeny of the Idaho GFkV reflects different sources of the virus-infected planting material brought to the state. In the absence of symptoms expressed in wine grape cultivars infected with GFkV, laboratory methods remain the only tool to detect the virus. To our knowledge, this is the first report of GFkV found in wine grapes in Idaho demonstrating its substantial presence in production areas.

References: (1) G. Gambino and I. Gribaudo. Phytopathology 96:1223, 2006. (2) R. A. Naidu et al. Plant Dis. 94:784, 2010. (3) S. Sabanadzovic et al. J. Gen. Virol. 82:2009, 2001.