The Effects of Viruses and Viral Diseases on Grapes and Wine

Grapevine is one of the plant species most susceptible to virus infections, which cause several complex diseases. The effects of viruses on grapevine performances are generally accepted as potentially severe, although an exact estimation is difficult because of the complexity of the factors influencing vine response (mixed infections, viral strain, environment, grape cultivar and rootstock, vineyard management, etc.). However, diseases like infectious degenerations caused by nepoviruses are clearly detrimental and dramatically affect plant vigor and yield. More controversial is the effect of members of the genera Ampelovirus, Closterovirus and Vitivirus, the causative agents of leafroll and rugose wood. In these cases, infected vines usually bear an adequate crop, so that growers are unaware of the real damage, especially to qualitative parameters. Sanitized vines usually present a more luxuriant growth and increased yield; therefore, cultivation practices (i.e., green pruning, bunch thinning, wider spacing, etc.) should be adjusted to cope with these enhanced performances. Grapevines are also affected by “minor” virus diseases (i.e., fleck, vein mosaic, rupestris stem pitting, etc.), whose impact is still unclear. Nevertheless, their presence should not be overlooked, because synergistic negative effects of their agents with other major viruses cannot be excluded. Viticulture currently faces new emerging virus diseases, such as red blotch (grapevine red blotch-associated virus) and leaf mottling and deformation (Grapevine Pinot gris virus), which threaten the profitability of the grape and wine industry. Viruses are dangerous and elusive pathogens whose presence in vines must be prevented by using clean propagation material. The new -omics technologies are expected to provide more information on plant-virus interactions.