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Title: Phylogeny of geminivirus coat protein sequences and digital PCR aid in identifying Spissistilus festinus (Say) as a vector of Grapevine red blotch-associated virus

item BAHDER, BRIAN - University Of California
item JAYANTH, MAYA - US Department Of Agriculture (USDA)
item ZALOM, FRANK - University Of California
item Sudarshana, Mysore

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2016
Publication Date: 7/27/2016
Citation: Bahder, B.W., Jayanth, M., Zalom, F.G., Sudarshana, M.R. 2016. Phylogeny of geminivirus coat protein sequences and digital PCR aid in identifying Spissistilus festinus (Say) as a vector of Grapevine red blotch-associated virus. Phytopathology. doi: 10.1094/PHYTO-03-16-0125-FI.

Interpretive Summary: Grapevine red blotch-associated virus (GRBaV) is a single stranded DNA virus, proposed to be a member of the family Geminiviridae, and is associated with grapevines showing red blotch symptoms in North America. The existence of the virus was reported in 2012, and subsequently detected in grapevines in major grape production regions. We investigated if a vector exists that can transmit GRBaV in vineyards. Phylogenetic analysis of the predicted amino acid sequence of coat protein (CP) of GRBaV with the CP of 23 geminiviruses representing all seven genera of the family Geminiviridae revealed that GRBaV-CP was most similar to that of Tomato pseudo curly top virus, a geminivirus known to be transmitted by a treehopper (Membracidae) which is closely related to leafhoppers (Cicadellidae). To identify vectors of GRBaV, hemipteran species within and nearby wine grape vineyards where virus spread was suspected were collected and transmission assays conducted. Among the species tested, the three-cornered alfalfa hopper, Spissistilus festinus (Say) (Hemiptera: Membracidae) was able to both acquire the virus from a grapevine infected with GRBaV and transmit the virus to healthy grapevines in the laboratory. In commercial vineyards, lateral shoots of grapevines girdled due to feeding injury by the adult three-cornered alfalfa hopper also tested positive for the virus using digital PCR. These findings represent an important step in understanding the biology of GRBaV and develop management guidelines.

Technical Abstract: Grapevine red blotch-associated virus (GRBaV) is a newly identified virus of grapevines, and a putative member of a new genus within the family Geminiviridae. This virus is associated with red blotch disease that was first reported in California in 2008. It affects the profitability of vineyards by substantially reducing fruit quality and ripening. In red-berried grapevine cultivars, foliar disease symptoms consist of red blotches early in the season that can expand and coalesce across most of the leaf blade later in the season. In white-berried grapevine cultivars, foliar disease symptoms are less conspicuous and generally involve irregular chlorotic areas that may become necrotic late in the season. Determining the GRBaV genome sequence yielded critical information for the design of primers for PCR-based diagnostics. To date, GRBaV has been reported in the major grape-growing areas in North America and two distinct phylogenetic clades have been described. Spread of GRBaV is suspected in certain vineyards but a vector of epidemiological significance has yet to be identified. Future research will need to focus on virus spread, the production of clean planting stocks, and the development.