Geraldine Diverres | Danielle Fox | James Harbertson | Manoj Karkee | Markus Keller

Response of Riesling Grapes to Temporally and Spatially Heterogeneous Soil Water Availability

Geraldine Diverres, Danielle Fox, James Harbertson, Manoj Karkee, and Markus Keller*
*Washington State University, 24106 N Bunn Road, Prosser, WA, 99350 (mkeller@wsu.edu)

Regulated deficit irrigation (RDI) and partial rootzone drying (PRD) have produced diverse viticultural and enological outcomes when implemented in vineyard settings around the world. Most research on deficit irrigation strategies has focused on red wine grape cultivars, optimizing attributes important for red wine production, which differ from white winemaking. A three-year field trial was conducted in southeastern Washington with Riesling winegrapes to compare the effect of RDI and PRD with a no-stress control and test their suitability for premium white wine grape production in arid climates. Irrigation scheduling was based on soil moisture thresholds according to vine phenological stage, rather than adhering to specific time intervals. Irrigation water supply, soil and plant water status, canopy size, yield components, and fruit and wine composition data were collected. Midday leaf water potential (Ψleaf) remained stable near -0.7 MPa until the extractable soil water content declined to ~35% (field capacity is at 100%). Beyond this point, Ψleaf declined as soil moisture decreased further, dropping to values as low as -1.5 MPa. Both RDI and PRD conserved irrigation water compared to the control, but both deficit practices also reduced yield. Seasonal variation had a more pronounced effect on basic fruit composition than irrigation practices. Preveraison water deficit, even if slight, reduced canopy size and yield while significantly affecting the volatile composition of the resulting wines. The wine phenolic composition was affected to a lesser extent by irrigation. This research confirms the power of small differences in preveraison water status to manipulate wine style in the vineyard and explores the relationship between the available soil water content and vine water status, using Riesling as a model.

Funding Support: USDA-NIFA Cyber-Physical Systems Program, Washington State Grape and, Wine Research Program, Chateau Ste. Michelle Distinguished Professorship.

Karine Pedneault | Karine Delorme | Frédéric Pitre | Paméla Nicolle

Metabolomic Response of Vitis vinifera and Interspecific Hybrids to Water Deficit and Heat Stress

Karine Pedneault,* Karine Delorme, Frédéric Pitre, and Paméla Nicolle
*Université du Québec en Outaouais, 78 rue Principale, Canada 
(karine.pedneault@uqo.ca)

Recent projections of increased temperatures linked to greenhouse gas emissions suggest an increased incidence of heat waves in Canada by 2100. In this context, vineyards will likely face more heat stress along with drier conditions, causing water deficit at critical periods of their development, including when new plots are established.

Interspecific hybrids varieties are issued from complex breeding programs involving Vitis vinifera and other Vitis species such as Vitis riparia and Vitis labrusca. In the context of global changes, interspecific hybrids bred for challenging environments such as cold climates are often expected to show greater resilience to stress than V. vinifera varieties. However, this assumption has been little studied. To fill this gap, we compared the metabolic response of young V. vinifera cv. Cabernet franc and Riesling and interspecific Vitis spp. Marquette and Vidal to heat stress, mild water stress, their combination, and a control under unstressed conditions over 21 days. Leaves were sampled, extracted, and analyzed by liquid chromatography-mass spectrometry-Orbitrap.

Over 200 metabolites were detected, including amino acids, phenolic compounds, and sugars. Depending on the variety, between 50 and 70 metabolites increased significantly in plants subjected to heat, water deficit, or combined stress treatments. Heat stress generated the strongest response, but combined stress provided mixed results among varieties. For instance, most metabolites upregulated by heat stress in Cabernet franc increased further when plants were exposed to combined stress. In Marquette and Vidal, most upregulated metabolites showed a lower response during combined stress. These results suggest that the stress mitigation mobilized fewer metabolic resources in Marquette and Vidal than in Cabernet franc, which could relate to a higher resilience in these varieties.

Funding Support: NSERC; AAFC; CGCN

Pietro Previtali | Thomas Giagou | Luis Sanchez | Nick Dokoozlian

Effect of Irrigation Timing and Intensity for Heatwave Mitigation in Cabernet Sauvignon Grapes and Wines

Pietro Previtali,* Thomas Giagou, Luis Sanchez, and Nick Dokoozlian
*E. & J. Gallo Winery, 1541 Cummins Drive, Modesto, CA, 95358 (pietro.previtali@ejgallo.com)

Extreme heat and drought events are becoming increasingly frequent and constitute a threat to grape production. Heatwaves are defined as two or more days with maximum temperature >38°C, and are known to negatively affect vine performance, yield, and wine quality. We conducted a meta-analysis to link historic climate, yield, and grape composition data across five ranches in the Napa region to approximate heatwave effects at the commercial scale. Cultural practices are needed to effectively mitigate heatwaves in the vineyard; in this case, increased irrigation during heatwaves was studied in Cabernet Sauvignon. Irrigation intensity (50% or 100% more than the control) and timing (zero, one, or two days prior to the heatwave) were evaluated. Experimental treatments were compared to the control: deficit-irrigated at 80% crop evapotranspiration through the heatwave. The trial was conducted in California at two sites, Lodi and Sonoma. The 2022 season was characterized by two postveraison heatwaves, one in mid August (four to five days, Tmax = 40.2°C) and one in early September (six to nine days, Tmax = 46.5°C). Across the two sites, additional irrigation effectively improved plant water status and physiological activity. Berry dehydration rates were significantly decreased by the most irrigation (9%) compared to the control (up to 22%), resulting in larger yields at harvest. Additional irrigation mitigated rapid total soluble solids increases observed in the control (up to 6 Brix/week). Incremental increases in irrigation levels during heatwaves resulted in wines with reduced levels of heat damage. The concentration of negative aroma compounds was greater in heat-affected wines, and that of positive fruity esters was less. Phenolic compounds were greatly affected by heat, which translated directly into lower color intensity, higher hue, and lower concentration of mouthfeel-related phenolics.

Funding Support: E. & J. Gallo Winery

Megan Bartlett | Alexander Ritter-Jenkins | Argimiro Sergio Serrano Parra | Nikita Kodjak | Dario Cantu | Andrew McElrone | Thorsten Knipfer | Ken Shackel

Precisely-Timed Irrigation Pulses can Reduce Berry Cell Death and Late-Season Dehydration

Megan Bartlett,* Alexander Ritter-Jenkins, Argimiro Sergio Serrano Parra, Nikita Kodjak, Dario Cantu, Andrew McElrone, Thorsten Knipfer, and Ken Shackel
*University of California, Davis, 595 Hilgard Ln, Davis, CA, 95616 (mkbartlett@ucdavis.edu)

Hot, dry conditions can exacerbate late-season berry dehydration, reducing yield and altering berry sensory properties. Late-season dehydration occurs when the berries undergo cell death in the mesocarp and the water released from the ruptured cells evaporates through the skin or is drawn from the fruit to the canopy by a water potential gradient (backflow). Here, we tested whether short pulses of increased irrigation would be a water-use efficient strategy to reduce late-season dehydration by interrupting stress-induced signals for berry cell death. We compared three irrigation treatments: conventional (following standard commercial practices) and an early- and a late-pulse treatment, where irrigation was increased by 40% in the two weeks immediately before or after the expected onset of cell death. We measured mature Cabernet Sauvignon vines grafted to 101-14 in an experimental vineyard at UC Davis in summer 2022 and 2023. We monitored vine water stress, berry cell death and shrivel, reactive oxygen species (H2O2) concentrations, and markers for cell oxidative damage (malonyldialdehyde, MDA). The late-pulse treatment significantly reduced the rate of cell death and the magnitude of berry shrivel at harvest over the conventional treatment. However, the early-pulse treatment did not significantly affect the rate or date of onset for cell death or shrivel. Concentrations of the reactive oxygen species H2O2 and markers for oxidative damage to cell membranes (MDA) increased at the same time as cell death, consistent with a role in programmed cell death, but were not significantly different among treatments, indicating that other mechanisms regulate irrigation effects on berry cell death. Overall, these findings show that the onset of cell death is not affected by water status, but a short pulse of irrigation soon after onset can slow the rate of cell death and reduce berry shrivel at harvest.

Funding Support: American Vineyard Foundation

Charles Obiero | Markus Keller

Extreme Drought Depresses Vine Growth and Yield Regardless of Fruit Removal

Charles Obiero* and Markus Keller
*Washington State University, 24106 N Bunn Rd, Prosser, WA, 99350 (charles.obiero@wsu.edu)

Frequent drought episodes during fruit development threaten sustainable production of premium winegrapes in the western United States. During an extreme drought event, the irrigation water supply to vineyards may be shut off and growers often remove fruit to ensure vine survival. This study investigated the idea that fruit removal during drought enhances vine survival in Cabernet Sauvignon and Riesling. In 2022 and 2023, irrigation water was shut off either at fruit set or at veraison, and 0, 50, or 100% fruit was removed at the start of each drought period. The outcomes were compared with standard regulated deficit irrigation (RDI), with and without fruit removal. Drought from fruit set or veraison lowered the vines’ water status alike, and the effect was greater in vines with no fruit removed in both cultivars. Canopies of vines exposed to drought stress from fruit set were up to 5.6°C warmer than the RDI vines. Drought starting at fruit set depressed yield more than drought starting at veraison in both cultivars. Vines exposed to drought from fruit set had more than 45% (Riesling) or 60% (Cabernet Sauvignon) less yield than RDI vines. Drought and fruit removal had no clear influence on fruit composition. Compared to the RDI vines, there was more than a one-third reduction in early-season shoot growth and a 40 to 50% drop in the number of flowers in vines exposed to drought stress the previous year, even if fruit had been removed from those vines. Our findings demonstrate that extreme drought will have a long-lasting effect on vine growth and productivity, regardless of fruit removal.

Funding Support: USDA Northwest Center for Small Fruits Research