Posts Tagged: viticulture

Researchers pinpoint drought-resistant traits in grape rootstocks

Findings could help wine industry adapt to climate change

Scientists at UC Davis have identified new root traits that help grapevines resist drought. The findings, published in the journal Annals of Botany, could speed up the development of grape rootstocks that protect vines from dry conditions, helping the grape and wine industry adapt to climate change.

The research, led by Department of Viticulture and Enology Assistant Professor Megan Bartlett, comes as 80% of California is experiencing extreme drought.

Most grapevines are not rooted directly into the ground but are instead grafted onto a rootstock, which forms the underground part of the plant and supports growth above ground.

“Rootstocks are an important tool to manage water stress,” Bartlett said. “Our goal was to identify traits that make rootstocks drought tolerant, so that grape breeders can amplify these traits in new varieties.”

Root cell traits

The study focused on traits measuring drought responses in living root cells.

The research specifically identified capacitance – which measures how much roots shrink as they dehydrate – as an important trait for drought tolerance.

“The water that enters the roots has to cross through a band of living cells to reach the xylem – the network of pipes that carries water up to the leaves,” said Bartlett. Most research has focused on xylem traits, but the living cells are often the first to be damaged during drought.

Water stress can shrink, deform, or even kill the living cells, causing the roots to shrivel away from the soil and lose access to the remaining soil water. Vines are then unable to replace water lost to evaporation and are forced to close the stomata – the small pores on the leaves that take in carbon dioxide for photosynthesis – to prevent severe dehydration. But closing the stomata stops photosynthesis and starves the vine of the sugars it needs to grow and ripen fruit.

This study is the first to test whether traits measuring root shrinkage and cell collapse can capture differences in rootstock drought tolerance.

Cell traits and drought tolerance

The researchers grafted Chardonnay onto eight commercial rootstocks. Half of the vines experienced drought conditions and half were kept well-watered in a greenhouse experiment.

The study found the eight rootstocks were surprisingly diverse and varied widely in their traits. The rootstocks also appeared to acclimate to drought by changing their traits in that the droughted vines were less susceptible to shrinkage and cell collapse than the well-watered vines.

Among the traits, capacitance was especially important for drought tolerance. The rootstocks with a lower capacitance (less root shrinkage) were better able to maintain photosynthesis during drought than other rootstocks.

“This research gives us a new trait to target for breeding more drought tolerant rootstocks,” study co-author and Ph.D. student Gabriela Sinclair said.

The research was supported by the American Vineyard Foundation, UC Davis, and by donations to the department from the Rossi family. Researchers at the University of British Columbia and the USDA-ARS Crops Pathology and Genetics Research Unit also contributed to the study.

Increasing temperatures led to better-tasting wine grapes, but for how long?

Study shows sugar, color content should be watched

Warming temperatures over the past 60 years have led to increased wine quality, but a new study looking at sugar and color content in grapes indicates the industry may be facing trouble if trends continue, according to collaborative research out of the University of California, Davis, and University of Bordeaux.

“Quality has increased steadily up to now,” said lead author Kaan Kurtural, a professor of viticulture and enology and an extension specialist at UC Davis. “We just don't know the tipping point.”

Kurtural's research, published in the journal OENO One, focuses on two renowned wine regions — Napa Valley and Bordeaux, France.

Researchers looked at ripening, grape quality and temperature data over six decades in both regions and then confirmed the findings with a five-year trial in Napa. They also consulted wine ratings in publications like Wine Spectator to gauge consumer demand.

One key finding: As temperatures exceeded what was considered the optimal level for quality, the grapes produced better wines.

“Previous research had few field data, but a record of assumptions,” said Kurtural.

Other quality factors at play

Temperature is a factor, but the paper suggests that sugar and color content should not be discounted. The authors also identified a biomarker that affects taste, color and other factors that can be the bellwether for climate change in red-skinned wine grapes.    

“Temperature is always there,” he said. “Temperature is not your bellwether.”

Higher temperatures can harm grape composition, including color, taste and aroma. Researchers examined pigment and sugar content of five California vintages of cabernet sauvignon, finding that as the grapes got sweeter the skin and color deteriorated.

The degradation of these quality-related compounds and the observed plateaus of wine quality ratings suggests there can be too much of a good thing.

Researchers have long theorized that increasing temperatures from climate change would lead to shifts in wine-growing regions, opening up some new areas for vineyards and making others unsustainable.

That shift could be a boon to some economies and devastating to others, something the industry should watch.

“Since the 1980s, grapes got riper and they were able to make better flavor and color compounds,” Kurtural said. “Are we going to lose this or adapt more?”

Gregory A. Gambetta with the University of Bordeaux is a corresponding author on the paper.

For more information:

• Kaan Kurtural, Viticulture and Enology, cell 707-200-5378, skkurtural@ucdavis.edu
• Amy Quinton, UC Davis News and Media Relations, cell 530-601-8077, amquinton@ucdavis.edu
• Emily C. Dooley, College of Agricultural and Environmental Sciences, cell 530-650-6807, ecdooley@ucdavis.edu

Coastal grape growers can use less water during drought

Study finds using less doesn't compromise quality

California grape growers in coastal areas can use less water during times of drought and cut irrigation levels without affecting crop yields or quality, according to a new study out of the University of California, Davis.

The findings, published today (Sept. 1) in the journal Frontiers in Plant Science, show that vineyards can use 50% of the irrigation water normally used by grape crops without compromising flavor, color and sugar content.

It sheds new light on how vineyards can mitigate drought effects at a time when California is experiencing a severe water shortage and facing more extreme weather brought on by climate change, according to lead author Kaan Kurtural, professor of viticulture and enology and an extension specialist at UC Davis.

“It is a significant finding,” Kurtural said. “We don't necessarily have to increase the amount of water supplied to grape vines.”

Growers will also be able to use this information to plan for the next growing season. “Everybody's worried about what's going to happen next year,” he said.

Kurtural and others from his lab studied irrigation and cabernet sauvignon grape quality at a research vineyard in Napa Valley over two growing seasons, a rainy one in 2019 and a hyper-arid one in 2020.

They focused on crop evapotranspiration, which was the amount of water lost to the atmosphere from the vineyard system based on canopy size. The weekly tests used irrigation to replace 25%, 50% and 100% of what had been lost by the crop to evapotranspiration.

Researchers found that replacing 50% of the water was the most beneficial in maintaining the grape's flavor profile and yield. The level of symbiotic arbuscular mycorrhizal fungi, which help grapevines overcome stresses such as water deficits, was also not compromised. And the water used to dilute nitrogen application was also reduced, making the process more environmentally friendly. 

The water footprint for growing grapes also decreased. For both the 25% and 50% replacement levels, water use efficiency increased between 18.6% and 29.2% in the 2019 growing season and by 29.2% and 42.9% in the following dry year. 

While focused on cabernet sauvignon, most red grapes will respond similarly, he said.  

“In the end, drought is not coming for wine,” Kurtural said. “There doesn't need to be a tremendous amount of water for grapes. If you over irrigate in times like these, you're just going to ruin quality for little gain.”

Members of Kurtural's lab — Nazareth Torres, Runze Yu, Johann Martinez-Lüscher and Evmorefia Kostaki — are also credited as authors. 

University of California Agriculture and Natural Resources provided partial funding.

For more information, contact:

• Kaan Kurtural, Viticulture and Enology, skkurtural@ucdavis.edu
• Amy Quinton, UC Davis News and Media Relations, amquinton@ucdavis.edu
• Emily C. Dooley, College of Agricultural and Environmental Sciences, ecdooley@ucdavis.edu

Helping winemakers sustainably produce premium wine

Ten large, shiny tanks stand near the Robert Mondavi Institute for Wine and Food Science at UC Davis, holding more than a year of rainwater and the key to processing food and drink during a drought. The water tanks, and the teaching-and-research winery they support, are showing students and winemakers throughout the world how to reduce processing costs, improve wine quality, and protect the planet's dwindling natural resources.

“It's about self-sufficiency,” says Roger Boulton, UC Davis professor of enology and chemical engineering. “We're demonstrating how you can operate a winery, brewery, or any food processing plant with the water that falls and the sun that shines on your roof.”

The work is the latest in more than a century of trail-blazing viticulture and enology science at UC Davis. UC Davis researchers are working with Cooperative Extension specialists and farm advisors with UC Agriculture and Natural Resources to help winemakers and grape growers sustainably produce premium wine.

Water is critical to winemakers in drought-stricken California and beyond. Grapes aren't a very thirsty crop to grow, but keeping fermentors clean is another story.

A typical winery uses four to six gallons of water after the grapes are harvested to produce one gallon of wine, and most of that water is used to wash equipment. Boulton and David Block, chair of the UC Davis Department of Viticulture and Enology, are developing self-cleaning fermentors capable of recycling 90 percent of that water. The goal: affordable technology and alternative practices that use less than one gallon of water to produce one gallon of wine.

Winemakers currently remove sticky, fermented, grape residue from tanks with water and elbow grease. Clean-in-place technology replaces hand-cleaning with an automated system that sprays tanks with diluted solutions of potassium hydroxide and potassium bisulfate.

“The dairy industry has used clean-in-place technology since the 1960s and the pharmaceutical industry since the 1990s,” says Block, a chemical engineer and enologist who helped the pharmaceutical industry manage clean-in-place technology before coming to UC Davis in 2008. “It's a little different with dairy and pharmaceuticals, where poor sanitation can kill you, but the concept is similar.”

So the water tanks near the Robert Mondavi Institute have two functions, to store water captured during the wet season to use during the dry season when it's needed most, and to filter and purify the water as it's used and reused to clean fermentors.

“We will filter and reuse that water at least five times, hopefully one day up to 10 times,” Boulton says. “It's not waste water. It has no phosphates, no nitrates, and no chlorine. Clean-in-place technology represents a huge potential for water and labor savings.”

Industry is starting to notice.

“Clean-in-place technology is very attractive to us,” says Ashley Heisey, director of winemaking at Long Meadow Ranch in Rutherford and a UC Davis viticulture and enology graduate. “Water is such a critical issue. Long Meadow Ranch owners Ted, Chris, and Laddie Hall built our facilities with great concern for the environment, and thanks to UC Davis, we can take it one step further.”

In Sacramento, grocer Darrell Corti from Corti Brothers Market says where UC Davis leads, winemakers will eventually follow.

“What we know about grape-growing and winemaking is primarily due to the work they do at UC Davis,” Corti says.

A longer version of this story is in the magazine Edible Sacramento.

The fine art of spitting: Allowing underage students to taste alcohol

California's drinking age of 21 prohibits many undergraduate students from learning critical skills early in their academic careers — sensory skills that they will need when they move on to jobs in the multimillion-dollar winemaking, brewing, and food industries.

Not until students turn 21 can they taste the wine and beer they make and learn to assess its sensory quality. Learning the characteristics of a wide assortment of good (and not-so-good) wines and beers is an important component of winemaking and brewing. Having to wait until their junior or senior year to learn these skills is a disadvantage for these students.

Legislation (AB 1989) has been proposed by California Assemblyman Wesley Chesbro (D-North Coast) that will allow students, ages 18 to 21, enrolled in winemaking and brewery science programs to taste alcoholic beverages in qualified academic institutions. The students can taste, but not consume — which means they must learn the professional practice of spitting during the tasting process.

Professor Andrew Waterhouse, an enologist in the Department of Viticulture and Enology at UC Davis, notes that tasting is critical to the students' education.

“Winemakers taste wine daily during harvest to quickly make critical decisions as the winemaking is underway,” Waterhouse said. “Our students need to start learning this skill here, with our guidance. And, they also have to get over the embarrassment of spitting — after every taste.”

Chik Brenneman, the UC Davis winemaker, said that the bill, if passed, “will allow students to move on to the sensory program a lot sooner, before they've finished most of their winemaking classes. Earlier sensory training will help them when they go to work in the industry.”

Waterhouse said in an interview with NBC Bay Area, “If you don't have the experience of what wine tastes like as it's being made, then you're completely missing a critical skill, which you then have to learn on the job.”

If the legislation passes, it will benefit enology and brewing students at UC Davis, which is the only University of California campus to offer undergraduate degrees in viticulture and enology and in brewing science (an option within the food science major).

While parents of college students may worry that the bill will open the door to widespread drinking, Waterhouse and Brenneman both noted that the focus of the bill is so narrow that its impact will benefit a limited number of students, and that it's unlikely to lead to excessive drinking. They say that the over-21 students routinely spit what they're tasting in a standard industry manner, and that “drinking” in class is not a problem.

With passage of this bill, which is backed by the University of California, the state will join 12 other states that have allowed this educational exemption for students.

Read more:

• California legislative information on AB 1989
• NBC Bay Area: Reality check: Bill calls for underage tasting on college campuses, Feb. 27, 2014
• Bill by Wes Chesbro would allow underage beverage students to sip; PressDemocrat.com, Feb. 28, 2014

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