Virus and Virus-like Symptoms on Grapevines in Missouri Vineyards
Virus or virus-like symptoms are emerging in grapevines in Missouri vineyards. These typical virus symptoms serve as a visual guide for identifying possible virus or virus-like diseases, and for evaluating incidences of virus-like diseases. Although diagnosis simply by visual inspection may not be reliable, a routine visual screening of vineyards is the most convenient and economic practice of acquiring the current status of a disease epidemic in vineyards. This preliminary diagnosis and evaluation of disease incidence helps us make decisions of either sending vines for confirming diagnosis in a laboratory or pulling out vines if diseased vines decline dramatically and lose yield.
Shown here are photos taken from vineyards during last three years that represent characteristics of disease symptoms likely caused by virus or virus-like pathogens.
Grapevine leaf roll disease on Cabernet Sauvignon and Chardonel
Symptoms similar to those caused by grapevine leafroll-associated viruses were observed on Cabernet Sauvignon vines (Figure 1), and Chardonel vines (Figure 2). Infection by leafroll-associated viruses generally cause reddish leaves in red grape variety. For example, vines with red leaves can be seen in a Cabernet Sauvignon vineyard in late September and October (Figure 1a). Dark brown or reddish tissues appear between major green veins (Figure 1b, c). In early growing season, blades of leaves grow backward (Figure 1d). Virus testing in the laboratory proved that grapevine leaf roll-associated virus 3 was detected in the vines showing these symptoms.
On white grape Chardonel vines, leaves rolled backward and become curly, but did not turn red in late season (Figure 2a). In most cases, sick leaves become thick and brittle (Figure 2b).
Mosaic symptoms on Chardonel vines
Mosaic and chlorotic mottle symptoms were observed on some Chardonel vines (Figure 3). Green cuttings were collected and planted in potted soils. Newly emerged leaves from these cuttings show the same mosaic and chlorotic mottle symptoms as observed on sick vines in the vineyard. This preliminary observation suggests that the causal agents are innate in the cuttings, and most likely could be viruses.
Mosaic veins and short shoots on Chardonnay vines
In a Chardonnay vineyard, more than 90% vines show virus-like symptoms (Figure 4a). Diseased vines developed very severe symptoms including short, zig-zag internodes, small crinkled leaves, chlorotic interval tissues or mosaic veins, deformed or broken leaves with mosaic vines (Figure 4b and 4c). Similar symptoms appear on new vines grown from the cuttings of the sick vines (Figure 4d), suggesting the pathogens are living inside the vines. Vigor of the diseased vines declined considerably. The initial observations indicated that the disease appeared to be caused by virus or virus-like pathogens.