A Survey for Grapevine Viruses in Washington State ‘Concord’ (Vitis × labruscana L.) Vineyards

Within the United States, Washington is the number one producer of ‘Concord’ grapes and the number two producer of wine grapes. Previous studies in wine grapes revealed the presence of twelve different viruses in Washington vineyards. Despite what is known about viruses in wine grapes in Washington, virtually no studies have focused on viruses in Concord vineyards. To further understand the epidemiology of viruses in Washington State, a survey of Concord grapes was conducted in 2010 and 2011. Five hundred Concord vines were sampled and tested for the presence of virus, and five different viruses were found among 92 virus-positive samples. The most common virus found was Grapevine leafrollassociated virus 3 (51 samples), followed by Grapevine fanleaf virus (24 samples), Grapevine leafroll-associated virus 4 (nine samples), Grapevine leafroll-associated virus 2 (four samples), and Grapevine leafroll-associated virus 9 (four samples). The presence of viruses in Concord vineyards is of great concern for growers due to likely movement of virus diseases from Concord grapes to wine grapes that might result in economic losses to the grape industry. Introduction Within the United States, Washington is the number one producer of juice grapes (Vitis × labruscana L. ‘Concord’ and Vitis labrusca ‘Niagara’) and the number two producer of wine grapes (15). The grape and wine industry have an economic impact of about $8.6 billion at the state level and about $14.9 billion at the national level (23). With a role this large in the local and national economy, the grape industry has a very low tolerance for threats to its sustainability, particularly arthropod pests and pathogens. There are many different viruses and other graft-transmissible agents reported from all of the major grape-growing regions in the world. To date, twelve different viruses have been detected in Washington vineyards (Table 1) (15). Of these, Grapevine leafroll-associated viruses (GLRaVs) 1, 2, 3, 4, 5, and 9 have been documented in grapevines (Vitis vinifera) affected with grapevine leafroll disease (GLRD). This disease is considered the most devastating viral disease of V. vinifera cultivars (16) and is present in all major grape-growing regions in the world (10,12). GLRD accounts for 50-60% of global yield losses due to all grapevine viruses and is responsible for about 5-10% of the yield loss in Washington State (16). Of the six GLRaVs known from Washington, Grapevine leafroll-associated virus 3 (GLRaV-3) was found to be the predominant virus in Washington vineyards (11,16). Grapevine fanleaf disease caused by Grapevine fanleaf virus is another very serious viral disease of grapevines. It is cosmopolitan in distribution and can cause up to 80% yield loss in wine grapes, depending on the cultivar (4). Although much information is available on viruses in V. vinifera cultivars, comparatively little is known about viruses in grape cultivars native to North America, principally Concord and Niagara (11,12). Recently, GLRaV-3 was documented in Concord and Niagara 5 August 2013 Plant Health Progress grapes in Washington State (22). In contrast to wine grape cultivars, Concord and Niagara cultivars appear to have latent infections of GLRD. With latent infections of GLRD in these cultivars, the prevalence of the disease and its economic impact have received little attention. Table 1. Grapevine viruses reported from Washington State vineyards. * Represents direct submissions to GenBank. Other important aspects of grapevine virus epidemiology that have been largely ignored in Concord and Niagara vineyards are vector biology and control. The grape mealybug (Pseudococcus maritimus Ehrhorn) and the European fruit lecanium scale (Parthenolecanium corni Bouché) are known vectors of GLRaV-3 and GLRaV-1 in wine grapes (7,9), but their role in transmitting viruses in juice grape vineyards is unknown. Both vector species are present in Washington vineyards (8). A common occurrence in Washington State is the close proximity of Concord vineyards to wine grape vineyards, and sometimes, the two types of grapes are grown adjacent to each other. Because of the presence of GLRaV-3 in Concord vineyards, the close proximity of Concord vineyards to wine grape vineyards, and the presence of two known vector species in both types of vineyards, it is possible that Concord vineyards could be serving as reservoirs for infection of wine grape vineyards with GLRaV-3 or other viruses, depending on the presence of the appropriate vectors. The primary objective of this study was to survey Concord vineyards in Washington State to document the presence of grapevine viruses. By knowing exactly what viruses are present in Concord grapes, a better assessment can be made of the epidemiology of grapevine viruses in Washington State vineyards and the risk they pose to grape production. Collection of Plant Samples A total of 500 samples were collected between 2010 and 2011 from twelve different Concord vineyard blocks near Prosser, WA. In each vineyard block, 42 Concord vines were sampled randomly. Five leaves, proximal to main trunk and cordon, were detached at the base of the petiole, placed in sealed plastic bags and transported to the Washington State University-Irrigated Agriculture Research and Extension Center, Prosser, for analysis. Detection of Viruses Extraction of samples was accomplished using the protocol by Rowhani et al. (2000) (20) by grinding 25 g of petiole tissue in 5 ml of general extraction buffer (GEB; 1.59 g/liter Na CO , 2.93 g/liter NaHCO , 2% polyvinyl pyrrolidone, 0.2% Virus Year Accession No. Reference GLRaV-1 2005 Not available Martin et al. 2005 (11) GLRaV-2 2005 Not available Martin et al. 2005 (11) GLRaV-3 2005 DQ780885 Martin et al. 2005, Soule et al. 2006 (11,22) GLRaV-4 2006 Not available Naidu et al. 2011 (15) GLRaV-5 2006 Not available Naidu et al. 2011 (15) GLRaV-9 2008 EF101737 Jarugula et al. 2008* GRSPaV 2005 FJ943414 Martin et al. 2005, Alabi et al. 2010* (11,) GV-A 2010 Not available Naidu et al. 2011 (15) GV-B 2010 Not available Naidu et al. 2011 (15) GFLV 2008 EU573307 Mekuria et al. 2008* (11) GSyV-1 2010 GU372349 Mekuria and Naidu 2010* (11) GFkV 2010 AJ309022 Naidu and Mekuria 2010* (11)