Project Title: Epidemiology and management of viral diseases in Washington vineyards

Project Duration: July 2017 – June 2020

Principal Investigator: Dr. Naidu Rayapati, Professor, Plant Pathology (Virology)
Organization: Washington State University
Address: IAREC, 24106 N. Bunn Road, Prosser, WA 99350
Phone: 509-786-9215

Project Personnel:
Dr. Sridhar Jarugula, Research Associate
Dr. Chandra Thammina, Research Associate
Dr. Raphael Adegbola, Research Associate
Mr. Jati Adiputra, PhD Student
Mr. Arunabha Mitra, PhD Student
Ms. Kaitlin Hadaway, MS Student

Dr. Sandya Kesoju
Dr. Ray Folwell
Mr. Trent Ball
Wine Grape Growers


Managing viral diseases in vineyards is a top priority for sustainable growth of Washington’s grape and wine industry. Vineyard surveys and testing samples using molecular diagnostic assays and high-throughput sequencing (HTS) technology revealed the presence of fifteen viruses in Washington vineyards. Information on the current status of viruses documented in vineyards is used in grapevine certification and quarantine programs to implement proactive
measures for protecting Washington’s young wine industry from ‘alien’ viruses reported in grapevines worldwide. Among the fifteen viruses, Grapevine leafroll-associated virus 3 (GLRaV-3) causing leafroll disease was more found to be insidious and widespread than Grapevine red blotch virus (GRBV) causing red blotch disease in the State vineyards. Since GLRaV-3 and GRBV produce fairly similar symptoms in red-fruited cultivars and mild symptoms or no obvious symptoms in white-fruited cultivars, accurate diagnosis is fundamental for managing these two distinct diseases. Data on genetic variability of GLRaVs and GRBV provided additional knowledge for improved detection and management of leafroll and red blotch diseases.

Tobacco ring spot virus (TRSV) and Grapevine fanleaf virus (GFLV) were detected in vineyards showing fanleaf degeneration/decline symptoms. However, these two viruses were found sporadically in Washington vineyards. Field studies have shown that TRSV significantly affects vineyard lifespan and fruit yield, and the dagger nematode (Xiphinema rivesi) present in vineyard soil can spread TRSV from infected to healthy vines. Preliminary studies indicated that X. rivesi is unlikely to spread GFLV. Thus, GFLV can be eliminated by using virus-tested ‘clean’ plants due to the absence of its nematode vector, X. index, whereas management of TRSV requires a combination of ‘clean’ plants and post-planting management of dagger nematodes.

Large-scale testing of grapevine samples at commercial diagnostic services is prohibitively costly for growers to readily embrace diagnostics for managing viral diseases in vineyards. During this project, activities were conducted to improve viral diagnostic assays for reliable detection of GLRaV-3 and GRBV. In addition, an economic study was conducted to estimate the costs associated with testing for GLRaV-3 and GRBV by molecular diagnostic methods under non-commercial settings. The results showed that employing a simplified sample preparation protocol in combination with improved molecular diagnostics assays can offer costeffective methods for high-throughput and reliable detection of GLRaV-3 and GRBV in grapevine samples benefiting growers, nurseries and other end users.

Studies in commercial vineyards have shown that both GLRaV-3 and GRBV can cause significant impacts on fruit yield and grape quality in own-rooted and top-grafted red- and whitefruited wine grape cultivars. These impacts were found to be variable depending on the cultivar, season and vineyard location. These results provided a foundation to further elucidate grapevinevirus-environment interactions for a comprehensive understanding of impacts of viral diseases in
vineyards under diverse wine grape-growing climates. Field studies have indicated absence of vine-to-vine spread of GRBV and rogueing of infected vines followed by replanting with healthy cuttings can be used as a low-cost strategy to manage red blotch disease in vineyards. In contrast, rogueing to control GLRaV-3 was found to be successful in some vineyards, while this approach was not effective in other vineyards due to field spread of leafroll disease. This calls for
additional research to study the dynamics of disease epidemics in different AVAs under varying geo-climatic conditions and vector management tactics for implementing integrated, area-wide control strategies against leafroll.

The project results were disseminated to growers, viticulturists, crop consultants and regulatory agencies at industry-sponsored meetings and workshops and field staff during vineyard visits. The project results were shared with scientific and extension communities worldwide through publications in peer-reviewed journals, industry-magazines and presentations at professional scientific meetings.

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Pest & Disease //