There are in excess of 60 recognised virus and virus-like diseases of grapevines worldwide. Many have obvious detrimental effects on vines, shortening the productive life of the vineyard and causing loss in yield and quality of fruit, reduced vine growth and loss in cane pruning weight, graft incompatibility, and vine decline and death. Viruses can be spread by insect vectors, soil-borne nematode vectors or by using infected cuttings during standard grafting and propagation practices. Symptomless infections often occur and these infected grapevines may act as a reservoir for other sensitive varieties.
Grapevine leafroll-associated viruses
Approximately ten grapevine viruses are endemic to Australia. The main virus of economic importance to Australian viticulture is the group of grapevine leafroll-associated viruses (GRLaV). Leafroll is a serious disease of grapevines that is of major importance to viticulture world-wide. It is named for the distinct foliar symptoms that are observed on infected grapevines and often causes reduced quality and yield of fruit and/or reduced quality and production of wood for propagation, in addition to graft incompatibilities. Symptomless infections can occur and these infected grapevines may act as a reservoir of virus for other sensitive varieties.
Rugose wood of grapevines is a complex group of diseases characterised by modifications of the woody cylinder. The diseases are of major importance to viticulture worldwide, with the five observed in Australia being Kober stem grooving, corky bark, N33 stem grooving, corky wood and rupestris stem pitting.
Australian grapevine yellows disease (AGYD) is observed in many Australian grape growing regions from spring through to late summer and is associated with three phytoplasmas or simple bacteria. A higher incidence of AGYD occurs in the warmer inland districts of the Murray Valley in NSW and Victoria, the Riverland in NSW and the Riverland in SA. Symptoms associated with infection of white grape varieties include irregular chlorosis or yellowing of leaves, which is seen as reddening in red varieties.
Fleck disease primarily affects Vitis rupestris and is associated with grapevine fleck virus (GFkV). Many grapevine varieties and rootstocks infected by GFkV alone are symptomless, although infection may be associated with graft incompatibilities. Symptoms include clearing of the veinlets in infected leaves (they are stripped of colour) which can spread into a mosaic pattern in older leaves. Older leaves may also become distorted and curl upwards. Symptoms are observed in spring during mild weather and disappear with the onset of hotter temperatures.