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Davis, California

Wednesday, April 24, 2024

$163 billion grape industry at risk due to spread of grapevine red blotch virus with no known treatment

$3 million grant given to institutions in California and Oregon to address unknowns of disease and mitigate its effects on grape production, wine quality

Less than an hour from UC Davis, lie the towns of Napa and Sonoma, both hubs of the $163 billion US grape industry. California-grown grapes makes up 90% of the country’s wine production, yet they are at risk as a currently untreatable grapevine disease spreads rapidly across the country but especially in California and Oregon vineyards. 

The grapevine red blotch disease is caused by the grapevine red blotch virus, which was first identified as a virus by Mysore R.Sudarshana, a research biologist through the United States Department of Agriculture Agricultural Research Service (USDA-ARS) department of plant pathology in 2012. 

“It is of huge concern to the wine industry because the virus and the disease have only been recently discovered and there are many unknowns about the disease biology and management,” Sudarshana said via email.

Once the grapevine has become infected with this virus, the impacts on the wine include reduced sugar content and increased acidity. Lower sugar reduces the wine quality resulting in a decreased value of the fruit. Winemakers are unable to produce high quality, premium wines with these changes.

Aside from the wine quality, the disease also greatly impacts the crop yields of grape varieties. This can be seen more intensely on red wines, as it takes longer for the grapes to ripen, forcing growers to allocate more resources as the growing season lasts longer. In some cases, growers do not have the economic means to wait for the grapes to fully ripen, resulting in lost yield. For the grower and the winemaker, the disease holds great power to impact each year’s yield and quality of product. 

To address this urgent issue in the grape industry, UC Davis researchers received a $3 million grant from the USDA National Institute of Food and Agriculture to study the grapevine red blotch virus and identify possible vectors, or organisms that spread a pathogen, of the virus. This four year grant is in collaboration with researchers and team members from UC Davis, UC Berkeley, UC Riverside, Oregon State University and USDA-ARS at Davis. 

Spread throughout California and Oregon, the project team is interdisciplinary in nature with experts in entomology, economics, engineering, plant pathology, virology and viticulture. Due to the complexity of this issue and all that is still unknown, Anita Oberholster — the project director and cooperative extension specialist in the department of viticulture and enology — sees this diverse set of expertise as an asset of the grant.

“The advantage of the grant is that it is multiple year so you can really build upon it, and it is multidisciplinary due to its large enough budget that allows for everyone to be involved in it,” Oberholster said. 

With this funding, the research team plans on starting two highly similar experiments in California and Oregon in various grape production areas throughout the two states to build upon the little that is already known about this virus and its vectors.

Since the initial discovery and identification of this virus, Sudarshana, along with Frank Zalom, a professor of entomology and nematology, showed that the three-cornered alfalfa treehopper insect is a vector of the virus. But this study was conducted successfully in a highly controlled environment. 

Further study of this specific species of treehopper has shown that it can serve as a vector of the virus, although the insect does not favor grapevines when given legumes or alfalfa to feed on. Due to how quickly this virus is seen spreading, especially in California and Oregon, there may exist multiple vectors that vary depending on environmental factors across the country. 

Because of the complexity of this virus and the ways it can change in response to situational environments, more research is needed to fully understand the vectors of the virus. This grant will allow for further study of possible vectors and a deeper understanding of management possibilities.

“The first step is just understanding the ecology of this insect vector in this cropping system,” said Houston Wilson, a cooperative extension specialist in entomology at UC Riverside.

Since the three-cornered alfalfa treehopper is not one of the common grapevine pests, more research needs to be done to fully understand the patterns of this insect in order to effectively mitigate its impacts. To be able to create management practices, there needs to be more knowledge on how the insect vectors act in this specific cropping system of vineyards. Beyond the vectors, the movement patterns of the virus itself have to be better understood as well.

“There is so much about the basic biology and chemistry of the virus that we don’t understand yet, it is only when you really understand these things that you can target and control it to mitigate the effects,” Oberholster said. 

Throughout the next four years, the team hopes to find conclusive data that will be able to shape management practices and guidelines that will soon be able to help growers and winemakers make informed decisions. 

“This is all about education and helping [growers] make informed decisions,” Oberholster said. “We want to develop some really decent guidelines and it won’t be the end of this problem but we want to make good progress.”

This collaborative and interdisciplinary research project is making the first major steps to fully analyzing and understanding the grapevine red blotch virus while providing helpful insight to the growers and winemakers dependent on the health of vineyards. 

Written by: Alma Meckler-Pacheco — science@theaggie.org


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