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Recent Research: UCD Viticulture and Enology Department Discusses Current Work, Future Plans, More Research on Grapevine Water Use, Drought, Salt, and Heat Tolerance

by Curtis Phillips
February 12, 2019

Recent Advances in Enology and Viticulture, RAVE, is an annual symposium put on by the UC Extension to give the larger wine industry a first look at recently published research from the UC Davis Faculty. RAVE also serves the function of allowing the UC Davis Viticulture and Enology Department to give the wine industry updates on longer-term research project as well as the overall status of the Department itself. 

Viticulture is not my area of expertise, but from the look of it, UC Davis seems to be going all in on vine water use, heat, and drought resistance. Two newly-hired viticulture professors introduced at RAVE, Dr. Megan Bartlett and Dr. Elisabeth Forrestel, are expected to direct their research into reaching a “better understanding of grapevine physiology and cultivar diversity, and understanding grapevine responses to heat, drought and climate change.” Bartlett is a plant physiologist and joined the UCD Faculty in January 2019.

Forrestel was previously a postdoctorate fellow at UCD and describes herself as “an evolutionary ecologist and a field biologist.”

It looks like their differing approaches should not only complement each other’s research, as well as give us a look into a topic that seems poised to become an overwhelming concern, but should also fit in with the research being conducted by other viticultural researchers on the UCD faculty.

Another viticultural paper was presented by Dr. Kaan Kurtural from the UC Cooperative Extension. Kurtural provided an update for a multifaceted, multi-year, project that was described as having three goals:

  • Develop new tools to the study physiology of roots and rootstocks (water uptake and root distribution)
  • Extend these tools to the soil water monitoring at the field scale for use in precision agriculture
  • Compare rootstocks performances under different irrigation amounts and delivery methods

It is this middle objective that caught my eye. In looking into a vine’s physiology, Kurtural and his associates developed a promising method of measuring soil water that I find most exciting because of the implications such a tool would have for more precisely measure vineyard water status down to the individual grapevine.

The idea is to map the water distribution under the grapevines in three dimensions using the electrical conductivity of the soil. This is then combined with other methodologies like physiological measurements, laboratory of analysis of primary metabolites (anything required for growth and maintenance of the grapevine itself) and secondary metabolites (everything else), and geostatistical data, to build not-quite real-time map vine water status. These data should allow a better idea as to the available water on a finer scale than the individual vineyard block, perhaps down to the individual grapevine.

Kurtural also discussed the measurement of the δ13C. In short, carbon naturally has three isotopes. A stable isotope with a nucleus of 6 protons and 6 neutrons known as 12 C, a stable isotope with a nucleus of 6 protons and 7 neutrons known as 13C , and an unstable isotope with 6 protons and 8 neutrons known as 14C . The amount of each isotope in the atmosphere is 98.93% 12C and 1.07% 13C with only traces of 14C.

Plants fix CO2 from the atmosphere using an enzyme, Ribulose-1,5-bisphosphate carboxylase/oxygenase, or Rubisco for short. Under ordinary photosynthesis the catalysis kinetics of rubisco use 12C more readily than 13C. This means that all the organic molecules (organic means containing carbon) produced by the plant tend to have less 13C than the atmosphere. However, when the plant closes its stomata, due to water stress for example, the rubisco enzyme uses all the available CO2. This means that the sugars produced have more 13C than they would under normal circumstances.

Kurtural demonstrated that measuring the δ13C gave grapevine water status gives results that correlate well with plant physiological methods which provides a way to double check, or validate, the data from other sensing tools. If Kurtural’s work lives up to its promise, and proves to be something that can be used in a commercial vineyard, it should yield a tool that can be applied to most, if not all, vineyards. This gives viticulturists another tool to make sure that they are neither over watering or under watering their vineyards.

Kurtural's third goal about rootstocks, comparing rootstocks performances under different irrigation amounts and delivery methods, dovetailed with the presentations given by Ron Runnebaum, who discussed the current and future research at UC Davis into sustainable winemaking, and Andy Walker’s discussion about the current and future objectives of the rootstock breeding program at UCD. I have too much to say about the subjects raised by Runnebaum to discuss them this month, but since we’ve already noted the bulk of the viticulture topics discussed at RAVE I should probably mention Andy Walker’s talk.

UCD Viticultural and Enology Makes Grapevine Heat Tolerance and Drought Resistance a Priority
Andy Walker discussed the current and future objective of the UCD grape breeding program. About a decade ago, and after something like 15 years of prior work, UCD started releasing the Walker lab’s GRN (Grape Rootstock for Nematode resistance) series of rootstocks. As the acronym suggests, the primary, or at least the initial, objective of these rootstocks was to increase the number of available rootstocks that had robust resistance to the multiple types of nematodes, including dagger nematodes, root knot nematodes, ring nematodes and lesion nematodes. Of course these rootstocks also have to have resistance to Pierce’s disease and phylloxera or they aren’t going to do the industry too much good.

Having reached these goals, the Walker lab is now looking to:

• Add salt and drought resistance to the GRN rootstocks
• Add ring nematode resistance from V. rotundifolia
• Add virus tolerance and vigor control
• Genetic mapping to allow MAS (Marker Assisted Selection) and stacking / combining traits
• Campus rootstock trials comparing GRN rootstocks with 101-14 and 1103P standards
• Field trials (in collaboration with farm advisors/growers) and pre-release to Foundation Plant Services (FPS)

Adding drought resistance and salt tolerance to the GRN rootstocks, along with Kurtural’s work and the two recent hires, clearly demonstrates that the UCD Viticulture and Enology department is making water use a research priority on par with phylloxera, nematode, PD, and virus resistance or tolerance. Historically, we haven’t made drought tolerance a priority. If vines needed more water, we pumped more water. If the soil got salty, we pumped more water to push the salt down beneath the root-zone.

A cynical observer would be mistaken to dismiss this research emphasis as something that only for the big wineries in the Central Valley. While big wineries still produce something like 80 percent of the wine in the US, all of the premium winegrowing regions in North America west of the Rockies, from the Santa Guadalupe valley up to the Okanagan valley are experiencing conditions that would benefit from the use of more drought-tolerant rootstock. I for one am glad to see that this work is being done.

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