Red Blotch Research in 2020

In 2020, a number of projects were initiated by teams of enterprising scientists seeking to help stop the scourge of grapevine red blotch virus, a significant and costly disease affecting Western vineyards that, so far, has eluded definitive answers regarding spread and management.

Anita Oberholster, extension enologist at UC Davis is leading a project called, “Ecobiology, Impact and Management of Grapevine Red Blotch Virus and Its Vector(s) in California and Oregon Vineyards.” After receiving a $3 million from USDA-NIFA’s Specialty Crop Research Initiative (SCRI) in late 2019, it began in earnest this year. More than a dozen collaborators from UC Berkeley, UC Davis, UC Riverside, Oregon State University, University of Georgia, and USDA-ARS are working with Anita on the project.

Anita’s own recent research has revealed how GRBV affects the chemical composition of grapes to degrade the quality of the resulting wine, and confirmed that grapes were slower to ripen and had lower sugar content when infected with the virus. Waiting longer to harvest the grapes then dehydrating them can achieve sufficient sugar levels for producing wine, her research suggests, but it doesn’t make up for their lost phenolics (the compounds that produce color, mouthfeel, stringency and bitterness). Here, she’s continuing to work on fruit and wine quality.

Other team members are exploring managing the virus in the vineyard. Frank Zalom and Mysore “Sudhi” Sudarshana (UC Davis), Vaughn Walton (Oregon State) and Kent Daane (UC Berkeley) already have identified promising insect vector candidates beyond the three-cornered alfalfa hopper (TCAH), whose efficacy at transmitting the virus has not been replicated outside a laboratory setting. As the project overview states, because red blotch spreads in vineyards where TCAH has not been found, finding potential vector species is paramount.

And in previous research, collaborators Alec Levin and Achala KC (Oregon State) found that watering may mitigate some negative effects of GRBV, but deficit irrigation doesn’t help. (Note: Alec, Achala and their colleagues led a nine-part red blotch webinar series from this past fall. Recordings are on the Oregon Wine Research Institute website.) For growers trying to optimize their investment in infected vineyards, is rogueing the only answer?

Not necessarily. A study co-led by Cornell virologist Marc Fuchs suggests that if less than 30% of plants in a vineyard are infected, replacing them with clean plants can minimize losses. But for anything more than 30%, it’s advisable to remove the entire block. Otherwise, he says, “the virus moves like wildfire throughout the whole vineyard.”

Marc is a collaborator on another new red blotch project launched this year, using sensors to detect viruses, led by Luca Brillante, Fresno State assistant professor of viticulture. Titled “Remote Sensing-Assisted Scouting of Virus Infections in Vineyards,” or HYPERVID for short, the California-based project employs hyperspectral imaging (because viral infections affect light reflectance in leaves, detectable at wavelengths these sensors can “see”) coupled with machine learning to scout out red blotch (and leafroll) in vineyards, before symptoms appear. The project received $280,000 in late 2019 from California’s Specialty Crop Block Grant program for a three-year study through 2022.

With help from co-investigator, Napa County UC Cooperative Extension farm advisor Monica Cooper, HYPERVID research began in the 2020 growing season in vineyards from Fresno County to Napa County. Images were taken with hyperspectral cameras at ground level from tractors and ATVs using a range of wavelengths, coupled with virus testing of the same vines to analyze for a correlation between the images and virus-positive vines. The study is focused on red winegrape varieties with an emphasis on cabernet sauvignon. The goal is to develop a tool that could be adopted by commercial companies and made available to growers or included in decision-support systems.

At greater elevations, another virus project took flight in September 2020, using aerial hyperspectral imaging to detect and map symptomatic and asymptomatic infections at scale. Led by Cornell grape pathologist Katie Gold, funded by NASA and done in collaboration with its Jet Propulsion Lab (JPL), the project deployed the Next Generation Airborne Visible and Infrared Imaging Spectrometer (AVIRIS-NG, JPL’s newest and best hyperspectral imager) over California vineyards to collect data to develop field and regional scale surveillance monitoring for viral diseases like red blotch.

Using the data collected this year and a new technique pioneered by scientists at NASA JPL, the team will determine how much “viral spectral signature” can be captured by both AVIRIS-NG and other imagers (from NASA, international space agencies and commercial satellite providers) at varying spatial and temporal scales. They will use these results to make recommendations to NASA about how their forthcoming satellite program can be used to immediately improve food security through plant disease surveillance and monitoring. One of the applied goals of the project is to develop new data products that can feed into field and regional level decision-support systems that enable growers to more strategically deploy high-accuracy ground diagnostics, such as the near-ground tools being developed by HYPERVID, to stop viral infections before they spread.

Understanding that red blotch and other viruses know no property lines, growers in California’s Lodi AVA are taking a regional approach. Led by the Lodi Winegrape Commission (LWC), an NGRA member-organization, the project advocates basic strategies to reduce virus spread, including decreasing vector populations, lowering virus inoculum, scouting vineyards for virus symptoms, testing symptomatic vines, rogueing individual vines that test positive when they make up 25% or less of the vineyard, removing the entire vineyard if more than 25% of vines are infected, and replanting vineyards with clean vines that are virus-tested from certified nurseries. Its 2020 milestone was the publication of a 138-page workbook, What Every Winegrower Should Know: Viruses, written by LWC Research and Education Director Dr. Stephanie Bolton, who serves on the NGRA Board.

“It is easy to see that an integrated, extensive virus outreach program is needed immediately,” Stephanie writes in the proposal establishing the collaborative research and integrated outreach effort, funded by the California Department of Food and Agriculture in 2018. Specifically referencing California, but in words that apply anywhere viruses live, she adds, “the industry needs stronger communication between growers, nurseries, laboratories, researchers and government programs to find a long-term strategy for lowering (our) inoculum and reducing the spread of viruses.”

This article was excerpted from these sources; click to read the full stories:
A Grape Virus Causes Vineyards to Lose $60,000 per Hectare, and There’s No Defense Against It, October 16, 2020, Massive Science
The Crush – September 2020 edition, California Association of Winegrape Growers