Issue link: http://read.dmtmag.com/i/123973
supports the concept that healthy vineyards produce both greater yield and higher quality of grapes, translating into better wine quality. Studies that compare infected and uninfected vines consistently show that the presence of certain viruses have drastic negative effect on both fruit set and quality In addition to the decline of vine health, GFLV was shown to interfere with the physical features of the berries, alcohol, tartaric acid and anthocyanins (color) in various grapevine varieties. The elimination of leafroll associated (e.g., GLRaV1, -2, -3) and Vitiviruses (e.g., GVA, GVB) showed increased vine vigor and fruit production in the vineyard. In the winery, the sugar content was increased while the juice acidity was reduced. Another study noted the beneficial effects on the aroma of produced wine; fruit from a muscat blanc variety subjected to disease elimination produced high- er soluble solids and higher amount of free and bound terpene, favorably affecting aroma character. In the vineyard, viruses and even strains of the same virus may be more or less aggressive than others causing disease. For example, certain strains of GLRaV-2 (red globe in the U.S., BD in Italy, and/or Alfie in Australia) are associated with graft incompatibility, vine decline and death. Other reports suggest that GLRaV-1 and -3 induce more severe symptoms than GLRaV-4 or -5. Certain strains of GVA can cause shiraz disease, a syndrome that induces delayed bud break, rubbery canes and premature death in syrah, merlot and gamay cultivars. So far, the disease has been observed in Australia and South Africa, in spite of Eurofins STA Laboratories detecting the same strains of GVA in grapevines from California vineyards without displaying characteristic disease symptoms. Finally, mixed infections of leafroll associated viruses and Vitiviruses can be lethal in some rootstock/scion combinations. Current studies are in progress at UC Davis with different rootstocks grafted to different leafroll species, which will enlighten our understanding on the effect viruses have in the vineyard and how it applies to winemaking. FREQUENT MONITORING While there is no clear answer to the question of which is the most important virus in the vineyard, we can definitely conclude that if a decline-causing virus such as GFLV is present, we can expect vine mortality within a few years. On the other hand, if leafroll and/or rugose wood viruses are present (depending on species or combination), we may expect vine decline over time accompanied by a decrease in the quality of fruit and subsequent reduction of wine quality. It may seem simple to discover and characterize new viruses infecting grapevines; however, it is much harder to determine their effect on cultivated wine grapevine varieties. Representative studies are required under many different climatic conditions using many rootstock and scion combinations to describe virus effects. In the meantime, effective disease control will require clean planting stock, along with frequent disease and insect monitoring to avoid potential infection. Judit Monis is manager of the Plant Health Services Division at Eurofins STA Labs in Gilroy, Calif. The lab provides disease testing services and specializes in grapevine clean planting stock and vineyard disease management. Monis may be reached at juditmonis@ eurofinsus.com or (408) 846-9964. Comments? Please e-mail us at feedback@vwmmedia.com. 74 V I N E YARD & WINERY MANAGEMENT | May - June 2013 w w w. v w m m e d i a . c o m