Arunabha Mitra, Sridhar Jarugula, Bhanupriya Donda, Emily Jordan, and Naidu Rayapati*
*Washington State University, WSU-IAREC, 24106 N Bunn Rd, Prosser, WA 99350 (naidu.rayapati@wsu.edu)

Among several viral diseases documented in Washington State vineyards, grapevine leafroll disease (GLD) continues to be an economically detrimental threat to vineyard health and productivity. Disease surveys have shown consistently that Grapevine leafroll-associated virus 3 (GLRaV-3, genus Ampelovirus, family Closteroviridae) is the most insidious and prevalent among four GLRaV species reported in Washington vineyards. Since GLRaV-3 occurs as multiple genetic variant groups in several grapevine-growing regions worldwide, this study was undertaken to examine genetic diversity of the virus in Washington vineyards. For this purpose, 2291 samples were collected between 2015 and 2019 from red- and white-fruited winegrape (Vitis vinifera) cultivars from 14 commercial vineyards in four American Viticultural Areas. Samples were tested for the presence of GLRaV-3 by RT-PCR assays, using primers specif- ic to a portion of the heat shock protein 70 homologue (Hsp70h) gene encoded by the virus. The ~607 base pair amplicons obtained from 818 samples were sequenced and compared with corresponding GLRaV-3 sequences available in public databases. In addition, total RNA preparations from 81 grapevine samples that previously tested positive for GLRaV-3 were subjected to Illumina high-throughput sequencing to generate near-complete viral genome sequences. These sequences were compared with GLRaV-3 sequences reported from other grapevine-growing regions. A global phylogenetic analysis revealed the presence of several GLRaV-3 variants in Washing- ton vineyards. Some aligned with six genetic variant groups (designated as I, II, III, V, VI, and IX) reported from other grapevine-growing regions. Among them, GLRaV-3 isolates belonging to variant group I were predominant in Washington vineyards. Information on the occurrence of genetically divergent virus isolates is providing insights for robust tracking of genetic variants and better understanding of the epidemiology of GLRaV-3 to improve management of GLD in vineyards.

Funding Support: Washington State University, Auction of Washington Wines, Washington State Wine Commission, Northwest Center for Small Fruits Research, and M. J. Murdock Charitable Trust.