Grapevine leaf roll disease (GLRD) is one of the most prevalent viral diseases in vineyards worldwide. At least 10 Grapevine leafroll-associated viruses (GLRaV-1 to -7, and -9, -10, and -11) are associated with GLRD. GLRaV-2 has a number of distinct isolates that are associated not only with GLRD, but also with graft incompatibility, young vine decline, and rootstock stem lesions. In the United States, GLRaV-2 isolates have been reported in the states of California (4), New York (1), Oregon, and Washington (3). A survey of grapevine viruses was conducted on seven grape cultivars, Norton, Chambourcin, Chardonel, Vignoles, Vidal Blanc, Traminette, and Cayuga White, in a vineyard located at Mountain Grove, MO during the falls of 2009 and 2010 and late summer of 2011. Vines from each cultivar were assigned into three blocks. From each block, six individual vines were randomly selected. Phloem scrapings were collected for detecting viruses by ELISA and reverse-transcription (RT)-PCR. To test for GLRaV-2, a set of primers, GLRaV-2-Forward (5′-GGTGATAACCGACGCCTCTA, nt 6745 to 6764) and GLRaV-2-Reverse (5′-CCTAGCTGACGCAGATTGCT, nt 7268 to 7287), were designed from the coat protein coding region as reported previously (2). GRLaV-2 was detected only in the samples of ‘Vidal Blanc’. The detection of GLRaV-2 was further verified by ELISA using GRLaV-2-specific antisera (Bioreba AG, Reinach, Switzerland). The GLRaV-2-infected ‘Vidal Blanc’ vines did not exhibit visible symptoms. The RT-PCR amplified 543-bp cDNA fragments were isolated from agarose gel and cloned into the pCR2.1 vector (Invitrogen, Carlsbad, CA). Plasmid DNA was purified from three individual clones and sequenced from both directions. Comparison of the 543-bp sequences showed that the sequences shared 99% nt identity with the corresponding regions of 21 GLRaV-2 isolates, including PMC-083 isolate from Croatia (GenBank Accession No. HM185277), LN isolate from China (GenBank No. FJ786017), SE isolate from Brazil (GenBank No. EU204909), and four isolates from Washington (GenBank Nos. EU760836, 760838, 760843, and 760848). ‘Vidal Blanc’ is a white interspecific hybrid grape. Absence of visible symptoms on this cultivar emphasizes the importance of planting certified grapevines that have been indexed for viruses. Discovery of GLRaV-2 in asymptomatic white grape cultivars will warn growers on the potential damages and epidemics of GLRD in Midwest vineyards and promote planting clean grapevines. To our knowledge, this is the first report of GLRaV-2 in grapevines in Missouri.
References: (1) M. Fuchs et al. Plant Dis. 93:395, 2009. (2) G. Gambino and I. Gribaudo. Phytopathology 96:1223, 2006. (3) R. R. Martin et al. Plant Dis. 89:763, 2005. (4) A. Rowhani et al. Phytopathology (Abstr.) 92:(suppl.):S71, 2002.