The Crush - March 2019 - 7

[ RESEARCH ]

New Red Blotch Study from UC Researchers

STUDY DISCOVERS HOW GRAPEVINE RED BLOTCH VIRUS DIMINISHES WINEGRAPE VALUE
By Jeannette E. Warnert
University of California Agriculture
and Natural Resources
Reprinted with permission

For the new research, the scientists
compared naturally infected winegrape
vines at the Oakville Station on two
rootstocks - 110 R and 420 A - with vines
grown on those two rootstocks that were
not infected. Grape clusters were collected
to examine differences in berry weight,
titratable acidity, pH and total soluble
solids.

Grapevine red blotch virus, a disease
that is dramatically reducing the value of
winegrapes in California's premium wine
production region, is harming plants by
inhibiting photosynthesis in the leaves,
according to research published this month
in the Journal of Agricultural and Food
Chemistry.
The new research also showed that
infected vines weren't able to conduct
water effectively, leaving whatever sugar
that was created by photosynthesis stuck
in the leaves. The accumulation of sugar
in the leaves results in reduced sugar in
the berries and lower-quality wine, said
UC Cooperative Extension specialist Kaan
Kurtural, one of the study authors.

"All those characteristics are important for
wine quality," Kurtural said. "Acidity and
pH effect palatability and storage potential.
Berry weight and soluble solids impact the
physical characteristics of the wine."
The grapevine red blotch virus impact
on anthocyanidins and tannins are a still
greater concern for winegrape growers as
they change the flavor profiles sought in
premium wines.
"High-value winegrapes are sold between
$7,000 to $23,000 a ton. If the winegrapes
don't have the profiles that winemakers are
looking for, they may only be valued between $1,500 to $2,000 per
ton," Kurtural said.

Grapevine with red blotch symptoms. Photo: Evett
Kilmartin, UCANR

According to the report, sucrose and its
monosaccharides were the vast majority of soluble sugars found
in the leaves. The leaf sugar tended to decrease in the ripening
process on red blotch negative vines. But this was not the case
in red blotch positive vines. As a result, grapevines infected with
the virus produce winegrape clusters with reduced sugar content,
poor color development and increased acidity.
Kurtural said the research will inform winegrape growers as they
consider possible treatments in vineyards with grapevine red
blotch-infected vines.
"There are some treatments that are being offered to growers, but
now that we better understand the disease, we know they won't
help," Kurtural said. "Growers don't have to replace the infected
vineyards immediately. But if 40 percent of vines are infected, they
may want to consider replanting. At least now we know what the
disease does, so they won't pay for snake oils."
Grapevine red blotch virus was first discovered in the Oakville
Experiment Station, UC Davis' research vineyard in Napa Valley,
in 2008. Since then, researchers found the virus in grapevines
throughout California and in 11 other states.

The research was conducted by UC Davis post-doctoral students
Johann Martinez-Buscher, Cassandra Plank, Runze Yu and
Luca Brillante in collaboration with Kurtural, UCCE viticulture
specialist Anita Oberholster, UCCE advisors Monica Cooper and
Rhonda Smith and UC Davis Foundation Plant Services academic
administrator Maher Al-Rwahnih.
Among the groups providing funding for the study were American
Vineyard Foundation and Allied Grape Growers.
ONLINE RESOURCES
* Study in Journal of Agricultural and Food Chemistry
https://pubs.acs.org/doi/pdf/10.1021/acs.jafc.8b05555
* UCCE Sonoma County - information and photos
http://cesonoma.ucanr.edu/viticulture717/Grape_Pests_and_
Diseases/
* Raul Girardello, UCD Department of Viticulture & Enology
http://lecture.ucanr.edu/Mediasite/Play/16382803b9cd49a4a7
4c50ef712facf71d

MARCH 2019 / 7

https://pubs.acs.org/doi/pdf/10.1021/acs.jafc.8b05555 http://cesonoma.ucanr.edu/viticulture717/Grape_Pests_and_Diseases/ http://cesonoma.ucanr.edu/viticulture717/Grape_Pests_and_Diseases/ http://lecture.ucanr.edu/Mediasite/Play/16382803b9cd49a4a74c50ef712facf71d http://lecture.ucanr.edu/Mediasite/Play/16382803b9cd49a4a74c50ef712facf71d

The Crush - March 2019

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