Grapevines are susceptible to approximately 70 different virus and virus-like diseases whose symptoms range from mild, with little economic impact, to severe — damaging and even killing infected vines. The transmission of viruses to healthy vines is a significant concern to grape growers, especially since infected vines cannot be cured once diseased. Therefore, understanding and managing virus transmission agents is critical. The newest viral threat to Oregon vineyards is the grapevine red blotch associated virus (GRBaV).
Dr. Vaughn Walton, associate professor and extension entomologist, OSU Department of Horticulture, with funding from the Oregon Wine Board, is studying GRBaV to understand transmission of red blotch and to identify vectors that may spread the virus (including insects). He is using a combination of data collection in the field and genomic testing in the laboratory. His research is supported by agricultural entomologist Dr. Rick Hilton at the OSU Southern Oregon Research and Extension Center and Danny Dalton, OSU senior research faculty assistant.
Grapevine red blotch associated virus is a newly-identified virus and, until its identification in 2012, symptoms of the disease were often mistaken for grapevine leafroll virus. To help growers accurately diagnose symptoms, Dr. Walton identified vineyards that tested positive for GRBaV and used sweep-net sampling and sticky-card monitoring to survey the vineyards and identify potential insect vectors including grape leafhopper, Western grape leafhopper and potato leafhopper. They identified several species of insects as potential vectors in all Oregon wine production regions. While an insect vector has not been confirmed, Dr. Walton is working with Dr. Mysore Sudarshana, USDA-ARS research biologist to conduct genomic testing. The team identified one potential vector in Oregon and are continuing further investigation. The only vector that is known for certain is the transfer of the virus by human activities.
To differentiate between grapevine leafroll and grapevine red blotch, the research team formulated new polymerase chain reaction (PCR) primers to determine the genomic composition of viruses found in infected vines. Using an ecological mapping tool, they then mapped infected vineyards to outline the corresponding spatial distribution of the viruses. They confirmed that the distribution of GRBaV does suggest insect vector transmission and the different distribution patterns found within vineyards indicate that different insect vectors may transmit different viruses.
Solving the complex puzzle of GRBaV and other leafroll viruses is extremely important for the economic sustainability of the Oregon wine industry. Through active collaboration with other scientists, Dr. Walton seeks to understand the complex epidemiology of these viruses and the corresponding insect vectors. Identification of these vectors may lead to integrated pest management solutions and proactive vineyard management strategies.