Five additional grapevines planted in the UC Davis Foundation Plant Services (FPS) Classic Foundation nursery block have tested positive for the presence of grapevine red blotch-associated virus (GRBaV). Red blotch disease, caused by GRBaV, shows symptoms similar to leafroll disease with discolored grape leaves in fall and reductions in grape sugar levels. Complete testing results were compiled and posted on the FPS website (fps.ucdavis.edu) this week, as part of a second phase of vine testing by FPS in its nursery blocks. Results of the first round of testing, released in February, identified three other vines testing positive for GRBaV at that time.
The FPS Foundation nursery blocks serve as sources of clean material for the grapevine nursery industry. Because of the recent emergence of red blotch virus, that was not previously identified or tested as part of the clean plant program, FPS began testing all of its grapevine material this year as a precaution. FPS has now tested 4,200 vines, about two-thirds of the Classic Foundation block on campus, and the entire Russell Ranch block where no vines tested positive.
One vine of each of the following selections tested positive for GRBaV. (Background information from the National Grape Registry, ngr.ucdavis.edu):
--Chardonnay 37—Imported by FPS from Champagne Perrier-Jouet, France in 1988, registered in 1997;
--Chardonnay 39—Imported from Dijon, France via Oregon State University (OSU) in 1988, planted in FPS vineyard in 1995;
--Chardonnay 41—Imported from I’Espiguette, France via OSU in 1987, registered in 1997;
--Chardonnay 49—Imported from Dijon, France via OSU in 1988, registered in 1997;
--Orange Muscat 02—From an Amador County vineyard.
The three vines testing positive for GRBaV based on results previously announced in February 2013 were:
--Chardonnay 68—A private clonal selection no longer listed as available from FPS;
--Thomcord 02—A black table grape selection, a cross of Thompson Seedless x Concord;
--Ruby Cabernet 02—A cross of Carignane x Cabernet Sauvignon developed by UCD Professor Harold Olmo.
All vines testing positive have been removed from the FPS vineyard, and will be used for research purposes. According to FPS analyst Carole Lamb, nurseries and growers who may have sourced wood from the vines testing positive have been contacted. “We tell them to test their own vines for GRBaV. Just because these vines tested positive in our vineyard this year, does not necessarily mean the budwood was virus positive when then acquired it,” Lamb explained. Clean vines (those testing negative) continue to provide clean budwood for most of the above selections from the Classic Foundation block.
All of the vines planted to date in FPS’ new Russell Ranch Foundation Vineyard have been tested and found negative for GRBaV. Planting at the 100-acre Russell Ranch, located ten miles from the UCD campus, began in 2011 with material propagated under the most stringent protocols required, established by the National Clean Plant Network (NCPN).
The older Classic Foundation block at the UCD campus will continue to be the main source of grapevine nursery dormant budwood for at least another year, until vines at Russell Ranch grow large enough to provide budwood. Lamb said green mist-propagated plants from Russell Ranch material are now being supplied on a limited bases. Testing of the final one-third of vines planted in the Classic Foundation block is expected to be completed this fall. FPS staff said these remaining vines and varieties are considered to be of lower priority for the industry.
A Fact Sheet on Grapevine Red Blotch Disease is available from NCPN (ncpngrapes.org). GRBaV has been detected in the following varieties in commercial vineyards: Cabernet franc, Cabernet Sauvignon, Chardonnay, Malbec, Merlot, Mourvedre, Petite Sirah, Petit Verdot, Pinot Noir, Riesling and Zinfandel. Red blotch has been identified in vineyards in California, New York, Virginia, Maryland, Pennsylvania, Texas, Washington and Ontario, Canada.
Red blotch has been studied in Napa Valley vineyards since 2008, when UC researchers suspected something other than leafroll was causing red leaf symptoms on vines. Separately and independently, researchers from Cornell University also identified red blotch in New York vineyards. Red blotch was formally introduced to the viticultural world at an international conference on grapevine diseases held in Davis in October 2012.
The California Rootstock Research Foundation agreed to provide money for research on GRBaV earlier this year, and the American Vineyard Foundation also awarded funds for red blotch research as part of its annual funding cycle in May.