Project Title: Epidemiology and Management of Grapevine Leafroll and Redleaf Diseases in Washington Vineyards
Project Duration: July 1, 2014 to June 30, 2017

Principal Investigator: Naidu A. Rayapati, Associate Professor (Virology)
Organization: Department of Plant Pathology, Washington State University Prosser, WA 99350.
Phone: 509-786-9215

Collaborator(s): Dr. Doug Walsh, Professor, Entomology, WSU-IAREC
Role: Collaborative research on vectors of grapevine leafroll disease.

Collaborator(s): Dr. Neil McRoberts, UC-Davis, CA
Role: Collaborative research on epidemiology of grapevine leafroll disease.

Collaborator(s): Drs. William Dawson and Siddarame Gowda, University of Florida, Lake Alfred, FL
Role: Collaborative strategic research on grapevine leafroll-associated viruses.

Cooperators: Growers, nurseries, industry stakeholders and regulatory agencies.
Role: Provide access to vineyards for sample collections, field data collection, extension and outreach activities.

Project Summary:

Viral diseases are recognized as one of the most serious impediments to the sustainability of Washington’s grape and wine industry. Due to the lack of curative measures, science-based knowledge is necessary for deploying alternative strategies to mitigate negative impacts of viral diseases. Towards this goal, a mix of fundamental and translational research was conducted to better understand viral diseases affecting Washington vineyards. Collaborative avenues and participatory approaches were pursued in partnership with grape growers to conduct these activities. Significant achievements of this project were highlighted in an article published in Good Fruit Grower August 5, 2016. The research-based knowledge was disseminated to various stakeholders by a variety of dissemination pathways. Research presented in this report was funded, in part, by the WSU Agricultural Research Center, the Wine Research Advisory Committee, the Washington Wine Commission, the Washington State Grape and Wine Research Program, WSDA Specialty Crop Block Grant Program, WSDA Grapevine Certification and Nursery Improvement Program, Washington State Commission on Pesticide Registration, Northwest Center for Small Fruits Research, and Altria–Chateau Ste. Michelle Wine Estates.

Vineyard surveys have indicated that grapevine leafroll disease continues to be a major problem, whereas red blotch and fanleaf degeneration and decline diseases are emerging concerns to Washington’s grape and wine industry. Virus indexing of grapevine samples have revealed that Grapevine leafroll-associated virus 3 (GLRaV-3) continues to be the most widespread among the viruses documented in many appellations. Leafroll and red blotch diseases produce similar, though not identical, symptoms in many red grape cultivars, whereas white grape cultivars showed no apparent symptoms of leafroll and red blotch diseases. Therefore, virus-specific diagnostic assays must be used for reliable detection of viruses associated with these two disparate diseases. Two nematode-transmitted viruses (Grapevine fanleaf virus and Tobacco ring spot virus [TRSV]) were detected in some wine grape cultivars showing fanleaf degeneration and decline symptoms. Using baiting assays, the spread of TRSV was demonstrated from symptomatic grapevines to healthy cucumbers and Cabernet franc vines by soil-inhabiting nematodes. Using morphological characteristics and genome sequence analyses, the dagger nematode Xiphinema rivesi was identified as a possible vector of TRSV.

Studies in commercial vineyards have shown that leafroll, red blotch, and fanleaf degeneration and decline can cause significant reduction in fruit yield and quality, especially sugars considered as the hallmark of wine grape quality. However, these negative impacts were found to be cultivar- and site-specific responses and likely influenced by genotype-by-environment interactions. Multi-season studies in commercial vineyards have shown continued spread of leafroll (predominantly GLRaV-3) into newly planted ‘clean’ vineyard blocks from external sources of infection. The spatial and temporal distribution of symptomatic vines in young plantings indicated that spread of leafroll during the initial years of post-planting likely occurs from heavily infected neighboring old blocks. In subsequent years, aggregation or clustering of symptomatic vines within young blocks was observed, suggesting secondary spread of leafroll between neighboring vines. Roguing of infected vines showed encouraging results to reduce viral incidence in new plantings. Outputs of the project are advancing sustainable disease management strategies in vineyards and strengthening the grapevine supply chain to prevent viral spread through planting stock.

Read more by downloading the full report above.

Pest & Disease //