Ecology and management of grapevine leafroll disease

Abstract

Grapevine leafroll disease (GLD) is caused by a complex of vector-borne virus species in the family Closteroviridae. GLD is present in all grape-growing regions of the world, primarily affecting wine grape varieties. The disease has emerged in the last two decades as one of the major factors affecting grape fruit quality, leading to research efforts aimed at reducing its economic impact. Most research has focused on the pathogens themselves, such as improved detection protocols, with limited work directed toward disease ecology and the development of management practices. Here we discuss the ecology and management of GLD, focusing primarily on Grapevine leafroll-associated virus 3, the most important virus species within the complex. We contextualize research done on this system within an ecological framework that forms the backbone of the discussion regarding current and potential GLD management strategies. To reach this goal, we introduce various aspects of GLD biology and ecology, followed by disease management case studies from four different countries and continents (South Africa, New Zealand, California-USA, and France). We review ongoing regional efforts that serve as models for improved strategies to control this economically important and worldwide disease, highlighting scientific gaps that must be filled for the development of knowledge-based sustainable GLD management practices.

Keywords: Closteroviridae; grapevine disease; integrated pest management; mealybug; vector.

FIGURE 1

Leaf symptoms of grapevine leafroll disease include inter-veinal reddening and leafrolling in red-fruited varieties. Symptoms are most pronounced around the harvest period. These photographs were taken in the fall (September) in Napa, CA, USA. Photographs show symptomatic leaf (A), group of leaves (B), and whole plant (C).

FIGURE 2

Estimated transmission efficiency of GLRaV-3 per individual per day (Ps; perSwallow, 1985) by different mealybug species, including studies that tested transmission by first and/or second instars, nymphs, adults, or mixed life stages, and used access periods of 1 day or longer. When available, only earliest life stages tested are included. From individual publications including multiple experiments, those experiments are combined to produce one estimate of Ps for each mealybug species. Results are based on a limited number of peer-reviewed publications per species; Pl. ficus – 5, Ps. longispinus – 3, H. bohemicus and Ph. aceris – 2, and Ps. calceolariae – 1. Figure shows Ps for individual publications (dark circles), mean (open circles), and standard error.

FIGURE 3

(A) Vineyards with high GLD incidence (dark red) serve as source of inoculum for adjacent blocks, in which disease spatial distribution is patchy, suggesting initial introduction of virus into uninfected blocks followed by within-block spread. (B) Example of secondary spread within rows, where an initial infection spread to neighboring plants. Both photographs were taken from the wine-producing region of Western Cape, South Africa.