T. A. Mekuria, Department of Plant Pathology, Washington State University, Irrigated Agriculture Research and Extension Center, Prosser 99350;
A. V. Karasev, Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow 83844;
R. R. Martin, USDA-ARS Horticultural Crops Research Laboratory, Corvallis, OR 97330; and
R. A. Naidu, Department of Plant Pathology, Washington State University, Irrigated Agriculture Research and Extension Center, Prosser 99350
In recent years, wine grape (Vitis vinifera) acreage in Idaho has expanded because of favorable climatic conditions for premium wine production. Nearly 95% of the 491.7 ha (1,215 acres) of wine grapes are in the Snake River Valley with Canyon County accounting for 81% of the vines. Previous studies have shown that grapevine leafroll disease (GLD) is the most widespread and economically significant virus disease in wine grapes in Washington and Oregon (1,2). However, little is known about the incidence and economic impact of GLD on wine grapes in Idaho. During the 2008 growing season, leaf samples were collected from approximately 25 individual grapevines of red-berried cultivars (Cabernet Sauvignon, Merlot, Syrah, and Petit Syrah) showing GLD symptoms and white-berried (Chardonnay) cultivars with suspected GLD symptoms growing in 10 geographically separate vineyards in Canyon County. An additional five samples were collected from a Lemberger block in Elmore County. Petiole extracts from these samples were tested by single-tube reverse transcription (RT)-PCR with primers LC 1 (5′-CGC TAG GGC TGT GGA AGT ATT-3′) and LC 2 (5′-GTT GTC CCG GGT ACC AGA TAT-3′) specific for the heat shock protein 70 homologue (HSP-70 gene) of Grapevine leafroll-associated virus-3 (GLRaV-3) (3). All samples, except the Petit Syrah, produced a single band of the expected size of 546 bp. ELISA with GLRaV-3-specific antibodies (BIOREBA AG, Reinach, Switzerland) confirmed the presence of the virus in samples that were positive in RT-PCR. GLRaV-3-specific amplicons were cloned in pCR2.1 plasmid (Invitrogen Corp., Carlsbad, CA) and 2 to 3 independent clones per isolate were sequenced in both orientations. A pairwise comparison of 22 sequences, six from Chardonnay (GenBank Accessions GQ344810, GQ344811, GQ344823, GQ344824, GQ344825, and GQ344826), five from Cabernet Sauvignon (GQ344807, GQ344808, GQ344809, GQ344827, and GQ344828), four each from Merlot (GQ344815, GQ344816, GQ344817, and GQ344818) and Syrah (GQ344819, GQ344820, GQ344821, and GQ344822), and three from Lemberger (GQ344812, GQ344813, and GQ344814) showed 87 to 100% identity at the nucleotide level and 92 to 100% identity at the amino acid level. A pairwise comparison of HSP-70 sequences of GLRaV-3 isolates from Idaho with corresponding sequences of GLRaV-3 isolates from GenBank showed nucleotide sequence identities between 88% (AJ748519) and 100% (DQ780885). Phylogenetic analysis of HSP-70 sequences from Idaho and GenBank showed clustering of Idaho sequences into five groups, with 12 sequences clustering with a Washington isolate (DQ780885), six sequences in a second group clustering with an isolate from Tunisia (AJ748522), two sequences in a third group clustering with an isolate from Austria (AJ748513), and one sequence each in groups four and five clustering with isolates from Italy (AJ748520) and Washington (DQ780889), respectively. The clustering was not cultivar- or vineyard-specific, suggesting separate introductions of different GLRaV-3 isolates in planting materials. To our knowledge, this is the first report of GLRaV-3 in grapevines grown in Idaho. These and previous results (1,2), indicate the wide distribution of GLRaV-3 in several grapevine cultivars in the Pacific Northwest Region.
References: (1) R. R. Martin et al. Plant Dis. 89:763, 2005. (2) R. A. Naidu et al. (Abstr.) Phytopathology 96(suppl.):S83, 2006. (3) M. J. Soule et al. Plant Dis. 90:1461, 2006.