Leafroll Virus Is Common in Cultivated American Grapevines in Western New York.

American grapevines (Vitis labrusca L. 'Niagara'; Vitis × labruscana L. H. Bailey 'Concord' and 'Catawba'; V. labrusca × V. riparia Michx. 'Elvira') from 24 vineyards in the New York portion of the Lake Erie production region (>13,000 ha cultivated) were tested to explore a possible relationship between virus infection and an unexplained fruit set malady in the district. One-year-old cane segments were collected 4 to 6 weeks before budbreak from 65 individual vines, which previously had been identified as malady positive or negative. Preparations from bark scrapings were tested for the presence of double-stranded (ds) RNA and for fan leaf degeneration virus, tobacco streak virus, and grapevine leafroll associated closterovirus-3 (GLRaV-3) by enzyme-linked immunosorbent assay (ELISA). Mechanical transmission of other potential viruses to Chenopodium quinoa was attempted with sap extracted from young shoots forced from intact segments of sampled canes. GLRaV-3 was detected in 17 (26%) of the sampled vines from eight (33%) of the vineyards, but there was no apparent relationship between infected vines and the fruit set malady. Vines of all four cultivars were infected. dsRNA was detected in all 17 samples positive for GLRaV-3 plus four additional samples. No other viruses were detected. Near harvest, nine vines (from two vineyards) previously testing positive for GLRaV-3 were examined and retested; all nine tested positive again, although none showed any overt symptoms of viral infection. This is believed to be the first report of GLRaV-3 from American grape vineyards in New York. The source of these infections is unknown: all vines were self rooted, the individual vineyards had been planted independently at different times, and V. vinifera and its hybrids are rare in the district. Wild grapevines (primarily V. riparia) are abundant in the region, although it has been reported that leafroll disease does not occur naturally in wild North American grapes (1). Nevertheless, our results indicate that cultivated American grapevines can be common reservoirs of GLRaV-3, and furthermore suggest the need to reassess the possibility that wild grapes also may serve as reservoirs of the virus. Trials are currently underway to determine possible effects of GLRaV-3 on cv. Concord, the most widely planted variety in the region. Reference: (1) A. C. Goheen. 1988. Leafroll. Page 52 in: Compendium of Grape Diseases. R. C. Pearson and A. C. Goheen, eds. American Phytopathological Society, St. Paul, MN.