The New Zealand perspective of an ecosystem biology response to grapevine leafroll disease

Grapevine leafroll-associated virus 3 (GLRaV-3) is a major pathogen of grapevines worldwide resulting in grapevine leafroll disease (GLD), reduced fruit yield, berry quality and vineyard profitability. Being graft transmissible, GLRaV-3 is also transmitted between grapevines by multiple hemipteran insects (mealybugs and soft scale insects). Over the past 20 years, New Zealand has developed and utilized integrated pest management (IPM) solutions that have slowly transitioned to an ecosystem-based biological response to GLD. These IPM solutions and combinations are based on a wealth of research within the temperate climates of New Zealand's nation-wide grape production. To provide context, the grapevine viruses present in the national vineyard estate and how these have been identified are described; the most pathogenic and destructive of these is GLRaV-3. We provide an overview of research on GLRaV-3 genotypes and biology within grapevines and describe the progressive development of GLRaV-3/GLD diagnostics based on molecular, serological, visual, and sensor-based technologies. Research on the ecology and control of the mealybugs Pseudococcus calceolariae and P. longispinus, the main insect vectors of GLRaV-3 in New Zealand, is described together with the implications of mealybug biological control agents and prospects to enhance their abundance and/or fitness in the vineyard. Virus transmission by mealybugs is described, with emphasis on understanding the interactions between GLRaV-3, vectors, and plants (grapevines, alternative hosts, or non-hosts of the virus). Disease management through grapevine removal and the economic influence of different removal strategies is detailed. Overall, the review summarizes research by an interdisciplinary team working in close association with the national industry body, New Zealand Winegrowers. Teamwork and communication across the whole industry has enabled implementation of research for the management of GLD.