A New Virus Disease Poses Additional Threat to Viticulture in Washington
A newly discovered grapevine virus is challenging Washington vineyard managers, just as it is challenging researchers to understand its nature and spread. Naidu Rayapati, a grape virologist at the Washington State University Irrigated Agriculture Research and Extension Center in Prosser, leads the team that is tackling this new threat to the Washington state viticulture industry.
Grapevine redleaf (or “red blotch”) disease in Washington vineyards had, until recently, been mistaken for another significant viral disease of Vitis vinifera, grapevine leafroll disease. Similarities in the visual symptoms — predominantly a red coloration of the leaves and a yield reduction in fruit harvest — made it difficult to determine that there were two different pathogens at work. When performing standard indexing for viruses in symptomatic vines, however, Rayapati discovered that some of these vines tested negative for viruses associated with grapevine leafroll disease. The cause of the symptoms was suspected to be a different, graft-transmissible virus.
As unknown viruses can be difficult to identify with traditional methods, Rayapati’s team used low-cost, high-throughput (or “next-generation”) genetic sequencing and discovered a single-stranded DNA virus of the Geminiviridae family in symptomatic grapevines. Nearly identical viruses have been discovered in New York and California, indicating that this virus may be widespread.
Transmission of the Virus
Geminiviruses are often spread by whiteflies or leafhoppers, so Rayapati wanted to know if this was the case with the newly discovered geminivirus. To begin with, WSU researchers allowed Virginia creeper leafhoppers, a pest of grapevines in central Washington, to feed on the leaves of infected grapevines, and then on the leaves of healthy grapevines. This simple experiment showed that, under greenhouse conditions, it is possible for Virginia creeper leafhoppers to spread the virus to uninfected plants. As leafhoppers commonly damage grape leaves, many growers already use chemical control for this pest. Controlling the insects is likely to contain the spread of the virus across vineyards.
Since cuttings from live grapevines are used for new plantings as own-rooted vines in many Washington vineyards, the geminivirus can spread through those propagation materials. When grafting grapevines, if either the rootstock or the scion is infected with the geminivirus, the resulting plants can be infected as well.
“This shows the importance of using planting stock that is virus-free, including plants from nurseries that are certified by the Washington State Department of Agriculture,” said Rayapati. “Washington State University is a partner in this effort, in that we provide science-based information to make sure the vines in certified nurseries are maintained virus-free.” Rayapati encourages growers to contact him for any additional information needed about the sanitary (infected) status of planting materials sourced from within or outside the state.
The Threat of the Virus
How serious is grapevine redleaf disease to Washington vineyards? Rayapati’s team has demonstrated that the disease can cause an average reduction in fruit yield of 20 percent in own-rooted Merlot and 35 percent in own-rooted Cabernet Franc. This loss in quantity is accompanied by a loss in quality, with significant decreases in sugars and anthocyanins. Tests also showed an increase in titratable acidity, while juice pH remained relatively stable.
Additional Research Needed
While WSU scientists have been quick to ferret out these details, there is much they still need to discover. “We are not sure at this stage whether the geminivirus alone is responsible for the disease symptoms. We would also like to study impacts of the disease on the quality of wine made from infected vines,” Rayapati said. “In addition, we are looking at another potential vector of the virus, the Western grape leafhopper, to determine its relationship with the geminivirus.”
One of the biggest questions involves the actual distribution of the virus to date. “The Wine Advisory Committee of the Washington Wine Commission considers it a high priority to survey vineyards for this disease,” said Rayapati. His team of graduate students and postdocs will be sampling grapevines around the state to determine how widely spread the geminivirus is and what grape varieties it affects. Individual growers will receive a confidential report of the results on their vineyards, while aggregated results will be used for industry-wide outreach and awareness programs.
“By working hand-in-glove with industry stakeholders,” said Rayapati, “WSU can provide science-based information quickly — information that both helps protect vineyards and advances the growth of the wine industry in Washington.”
Rayapati has recently published a paper on his research in the scientific journal PLOS ONE, available at bit.ly/14sZBqp. Sudarsana Poojari, a graduate student in Rayapati’s lab, is listed as the first author.
For more information on WSU research and extension involving viticulture, see http://wine.wsu.edu/research-extension.
-Bob Hoffmann
Riesling Bound: WSU V&E Student Selected for Professional Exchange Program to Germany
Colin Hickey is headed to Germany. The WSU Viticulture and Enology student was selected to participate in the 2013-2014 Congress-Bundestag Youth Exchange for Young Professionals. This program, funded by the U.S. Congress and its German counterpart, the Bundestag, provides young Americans and Germans the opportunity to spend one year in each other’s countries, studying, interning, and living with hosts on a cultural immersion program. Hickey, the only American student of viticulture and enology to be chosen this year from a competitive pool of 600 applicants, will jump the Atlantic at the end of July to begin his new experience. The program funds his travel, room and board, and university expenses.
“I’m a Westsider. I’ve lived in Washington all my life,” explained Hickey of his desire to live and study abroad. “I’d like to gain a new perspective.” This perspective will be provided by a year with cultural immersion, intensive language training, study at a university, and an internship — hopefully at a German vineyard and winery. He is particularly interested in seeing how German culture influences the production of Riesling, and how that differs from the American approach. As he is familiar with Pinot Noir from Oregon’s Willamette Valley, he is also interested in seeing how this variety is vinified in Germany, a nation that mainly produces white wines.
Hickey was recommended for this program by his mentor, Thomas Henick-Kling, director of the WSU Viticulture and Enology program who is also a native of Germany. Henick-Kling said that Hickey’s strong motivation and initiative make him a great match for the international program. “Colin is enthusiastic in his studies and his goals,” said Henick-Kling. “His contributions in class show that he is doing much literature research of his own. Colin does not hesitate to contribute with physical work when we are in a vineyard or in a winery.”
Hickey’s short term goal after returning from Germany is to finish two semesters of study at WSU in order to graduate. “After that,” says Hickey, “I want to work at a vineyard or winery, or perhaps even a wine-focused restaurant. My dream-come-true would be to become a winery owner.”
For more information about educational opportunities through the WSU Viticulture and Enology program visit http://wine.wsu.edu/education/.
-Bob Hoffmann
A Washington Wine Road Less Travelled: Touring the Wahluke Slope and Ancient Lakes AVAs
On a perfect blue-sky weekend in June, 20 winemakers and grape growers discovered a hidden adventure off the beaten path of central Washington wine country. The educational tour, organized and offered by the WSU Viticulture & Enology Certificate Program, covered six sites and included an informative and fascinating presentation by Dr. Joan Davenport, WSU soil scientist, aka “Dr. Dirt,” on the history and geology of Wahluke Slope and Ancient Lakes. Ancient Lakes is Washington’s newest AVA, designated in 2012.
The tour group consisted of winemakers, growers, and enthusiasts interested in entering the wine industry. Others came to make connections for grape purchases, to see vineyards they had only heard about, and seize the opportunity to talk informally with winemakers.
The four Wahluke Slope sites visited included J & S Crushing, Rosebud Vineyards, Milbrandt Vineyards, and StoneTree Vineyard. J & S Crushing, one of the largest privately owned bulk wineries in the state, made an impression with its sheer scale of operation. It produces about 2 million gallons of wine annually. Rosebud Vineyards, a family owned and operated business, was one of the first vineyards planted on the Wahluke Slope in the late 1970s; they grow 19 grape varieties on 140 acres. At Milbrandt Vineyards, Josh Maloney, head winemaker, and Jason Schlagel, head viticulturist, gave us a tour of the winery and vineyards, and an informative tasting of merlot wines from four different vineyards on the slope illustrated the differences in ‘terroir.’ The Wahluke day ended with a visit to StoneTree Vineyards, a major supplier of premium quality grapes. As we stood talking with co-owner and manager, Tedd Wildmann, and surveying the meticulous plantings of StoneTree, we had an expansive view of the entire AVA.
On the second day we visited White Heron Cellars and Cave B Estates in the Ancient Lakes AVA. At White Heron Cellars, owner and winemaker Cameron Fries shared the history of White Heron and his involvement with establishing the Ancient Lakes AVA. Then, at Cave B estates we were hosted by winemaker Freddie Arredondo who treated su to an extensive tasting of their fine wines and another expansive view of the gorge created by the powerful Missoula Floods.
Group comments ranged from delighted surprise at seeing the uniqueness of this area to appreciation for the knowledge and willingness of our hosts to share information about their vineyards and wineries.
These V&E Program tours are increasing the educational opportunities for those in the wine industry and those just entering the industry, and are increasing the visibility of Washington wine country’s hidden treasures. For more information about future WSU V&E Program tours, contact Theresa Beaver at tbeaver@wsu.edu.
For more information about the V&E Certificate program visit: http://wine.wsu.edu/education/certificate/.
-Theresa Beaver
Immerse Yourself in Washington Wine!
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Come see and taste why Washington wines are peak performers with more 90+ scores from Wine Spectator than any wine region in the world.” –Auction of Washington Wines
August 15 through 17 will be three fun and wine-derful days of events including wine tastings, winemakers’ dinners and a gala wine auction, in support of the WSU Viticulture and Enology program and the Seattle Children’s Hospital. More than 90 of Washington’s premier wineries will participate, pouring and discussing their vintages, and individual wineries will host special events with family-friendly activities. For more information, visit http://www.auctionofwashingtonwines.org/.