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Spatio-temporal spread of Grapevine leafroll disease in Washington vineyards
B. P. DONDA (1), R. Naidu (1). (1) Washington State University, Prosser, WA, U.S.A.

Grapevine leafroll disease (GLD) is one of the major constraints for Washington’s wine grape industry. We have been monitoring spatial and temporal spread of GLD in young vineyard blocks planted with virus-tested, own-rooted grapevine (<i>Vitis vinifera</i> L.) cultivars and located in close proximity to heavily infected old vineyard blocks. Symptomatic and asymptomatic grapevines, that are immediately adjacent to symptomatic plants, were tested by RT-PCR for the presence of <i>Grapevine leafroll-associated virus 3</i> (GLRaV-3, genus <i>Ampelovirus</i>, family <i>Closteroviridae</i>). A comparison of the disease incidence obtained from each block in 2013 season with data obtained from previous seasons showed higher number of grapevines with GLD symptoms in each season compared to previous season, suggesting increased disease incidence with time in young plantings. The spatial distribution of symptomatic grapevines showed a disease gradient in which the highest percentage of symptomatic grapevines were located in rows closest to the heavily infected old blocks and the disease incidence declined in rows with increasing distance from old blocks. Furthermore, the spatial distribution of symptomatic grapevines showed an aggregated pattern, suggesting vine-to-vine spread within individual rows in young blocks. Cloning and sequencing a portion of the heat-shock protein-70 <i>homolog</i> of GLRaV-3 confirmed virus spread from neighboring blocks to young vineyards planted with virus-tested planting stock.

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