Grapevine leafroll-associated virus

Grapevine leafroll-associated virus (GLRaV) is a complex of viruses classified within the Closteroviridae family and the Ampelovirus genus. It is recognized as one of the most economically damaging viral diseases in viticulture globally. The virus primarily affects the phloem tissues of the vine, disrupting the translocation of sugars and other essential nutrients from leaves to the berries and perennial parts of the vine.

The primary symptoms are leaf curling, which usually begins at the base of the shoot and moves upward towards the apex. In red-berried varieties, the leaves show a characteristic reddening of the interveinal tissues while veins remain green; in white-berried varieties, the tissues turn chlorotic or yellow. These symptoms become most pronounced during the late summer and autumn seasons, leading to significant physiological stress.

Transmission occurs through two primary routes: the use of infected propagation material and the activity of insect vectors. Mealybugs (Pseudococcidae) and soft scale insects (Coccidae) are the most significant vectors of GLRaV. They acquire the virus by feeding on infected phloem sap and inoculate healthy vines during subsequent feeding sessions. The virus is semi-persistently transmitted, meaning the insects can carry the virus for a limited period after initial exposure.

Environmental factors heavily influence the spread of the disease. Warmer climates generally support larger populations of vectors, leading to higher transmission rates in the field. The virus is not mechanically transmitted through pruning tools, but it persists within the wood, meaning that an infected vine remains a permanent source of inoculum within the vineyard unless it is completely removed.

Management of GLRaV relies on an integrated approach focusing on prevention and reduction of inoculum. Key control strategies include:

• Planting certified, virus-free nursery stock to ensure a healthy start.
• Continuous scouting for leafroll symptoms during the growing season.
• Roguing and removal of infected vines to reduce the source of the virus.
• Implementing rigorous insect management programs to suppress mealybug and scale populations.