| Grape -- Virus Diseases | |||
| Cause:
The viruses associated with grapevine leafroll disease and corky bark disease have been found in Oregon and Washington vineyards. Leafroll disease spreads through insect vectors, while corky bark either does not move in vineyards or move very slowly. Of the viruses associated with leafroll disease, GLRaV-3 was the strain most often found in surveys and was shown to be transmitted by the grape mealybug in Washington. Since there has not been any work on virus vectors of these viruses in grapes in Oregon, it is critical that growers continue to use only certified wood when establishing vineyards. All grapes entering Oregon and Washington are under quarantine and must be certified free of leafroll viruses. As more vines are grafted onto rootstocks to guard against Phylloxera, these viruses will become more damaging if they get established. Leafroll will cause symptoms in ungrafted plants but may cause graft union necrosis in grafted plants as will corky bark. Vitis vinifera cultivars that carry corky bark do not show symptoms until they are grafted onto American rootstocks.
Rupestris stem pitting associated virus (RSPaV) is in Oregon and Washington and is not listed as a quarantinable virus. It remains an important component of the Washington certification program, although California, Canada, France, and Germany do not have this virus listed as restricted in their certification schemes. It is generally accepted that RSPaV is a minor virus, though its effect in mixed or multiple infections is unclear. Three nematode transmitted viruses (Nepoviruses) are known to infect grapevines in North America. In a survey of vineyards known to have Xiphinema americanum nematodes, no Tomato ringspot virus, Grapevine fanleaf virus or Arabis mosaic virus was detected in Oregon or Washington. It is not expected that fanleaf would be a problem in Oregon, since the vector, X. index, was not found in more than 75 vineyards surveyed. Similarly, the nematode vector of Arabis mosaic virus is not widely distributed in North America. All grapevines entering Oregon and Washington must be certified free of these Nepoviruses. |
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| Symptoms:
Leafroll, also called red leaf or white emperor disease, reddens the lower foliage of dark-fruit cultivars in September and October. Foliage of white-fruit cultivars may yellow at this time. Other symptoms include delayed foliation in spring, downcurling of leaves, production of fewer, smaller clusters of berries lower than normal in soluble solids, and less vigorous vine growth in adverse circumstances. Red-fruit cultivars do not color well when infected with GLRaV. Potassium deficiency symptoms mimic many of the symptoms caused by GLRaV. The vein clearing associated with leafroll disease can be used to discriminate it from similar leaf discoloration caused by other stress factors.
All of the Nepoviruses are associated with poor fruit set in grapevines. Virus infection is characterized by loose clusters and abundant small shot berries. Fanleaf symptoms are best seen early in the growing season. New growth on infected vines often is dwarfed on weak, flattened, crooked canes. Young leaves are mottled and deformed, showing excessive dentation (abnormally sawtoothed leaf edge) and a broad sinus at the petiole. Together, these symptoms resemble a partially closed fan, much like 2,4-D injury. Some strains cause bright yellow patterns on leaves, often without the leaf deformation associated with other Grapevine fanleaf virus strains. Grapevine yellow vein virus is another strain, it produces distinct yellowish or whitish bands along leaf veins most of the season. The distribution of the yellow vein strain appears to be very limited at this time. Corky bark causes an incompatibility to develop at the graft union. Leaf symptoms resemble those of leafroll but are more severe on some rootstocks. Leaves on cultivars such as ‘Pinot Noir’ may develop a yellow chlorosis before they turn red. The wood at the base of canes may swell slightly, causing the bark to split. Depending on the cultivar, various wood grooving also may occur. On self-rooted grapevines, the symptoms of corky bark are very mild. Rupestris stem pitting associated virus is suspected of causing a slow decline of Vitis vinifera. Affected vines are smaller than healthy ones, but leaves appear normal. Delayed ripening and reduced yields have been associated with this problem. Rootstocks of V. rupestris and its hybrids develop pitting in the xylem, observed on woody tissues after bark is removed. Easily confused with corky bark symptoms. On self-rooted grapevines, RSPaV intensifies the symptoms associated with leafroll disease. |
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References: Golino, G., Uyemoto, J.K., and Goheen, A.C. 1992. Grape virus diseases, pp. 101-109. In: Grape Pest Management, Second Edition. D.L. Flaherty et al., eds. University of California: Oakland, CA. Martin, R.R., Eastwell, K.C., Wagner, A. Lamprecht, S., and Tzanetakis, I.E. 2005. Survey for viruses of grapevine in Oregon and Washington. Plant Disease 89:763-766. |
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| Content edited by: Jay W. Pscheidt on January 1, 2009 | |||
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