Summary The increasing incidence of wildfires in grape growing regions of California and the West Coast has highlighted the need for enhanced understanding of the levels of volatile phenols and their non-volatile glycoside precursors that contribute to smoke taint off-flavors in grapes and wines. In this project, we measured ten volatile phenols in non-smoke exposed grapes to begin to understand baseline levels of these compounds in red and white grape varieties. Free and total levels of guaiacol, 4-methylguaiacol (creosol), phenol, 4-ethylguiacol, o-, m-, p-cresol, 4- ethylphenol, 4-methylsyringol, and syringol were measured in grapes from different regions of California. Air quality data for these regions is also presented. The data show a high degree of variability across varieties, regions, and years indicating that it will be important to have large databases to assess the impacts of smoke exposure on free and total volatile phenol composition. We have submitted a proposal to continue this work in 2022-23
Summary: Vineyards face climate change, increasing temperatures, and drought affecting vine water status. Water deficit affects plant physiology and can ultimately decrease yield and grape quality when it is not well managed. Monitoring vine water status and irrigation can help growers better manage their vineyards. However, when field measurements, such as stem water potentials (SWP), can be precise, they are time-consuming. In addition, they do not allow for easy assessment of spatial variability, which is a critical factor for water status management. Remote sensing tools can help map plant water status in space and time and streamline data acquisition over whole vineyards several times during the season. In this project, we monitored a variably irrigated vineyard several times during the season with a hyperspectral NIR/SWIR camera mounted on a UAV. We worked in a Cabernet Sauvignon vineyard in the San Joaquin Valley of California equipped with an automated irrigation system. We created forty-eight independent watering zones and applied twelve different amounts of water replicated four times in a randomized block scheme. Water amounts were fractions of the grower allocation and applied as sustained and regulated deficit irrigation strategies. Hyperspectral images in 112 bands from 900 nm to 1700 nm were collected using a UAV every two weeks from June to harvest. Contemporarily, we measured vine water status through SWP, stomatal conductance (gs) and net assimilation (AN). For the analysis, the images were segmented to extract the canopy signal and converted to reflectance, then used to predict the field water status measurements using machine learning models. Models were evaluated using coefficients of determination (R2 ), and root mean square error (RMSE). Feature importance was also computed to determine the importance of each band in the model. Field measurements of stem water potential ranged from -2.0 to -1.14 MPa. The canopy signal was segmented from the soil background using a classifier with an accuracy of 99.7%. We tested random forest, gradient boosting machine, and support vector machine algorithms in a preliminary analysis to predict SWP values. The most performant model was the random forest, and it was able to predict SWP values with an R2 of 0.6 and an RMSE of 0.1 MPa as assessed in a 5-fold crossvalidation procedure. The most important bands for model prediction were 1146 nm, 1153 nm, 1321 nm, 1363 nm, and 1434 nm, all situated in water absorption domains. These promising results demonstrate that SWIR images can monitor the field’s vine water status and inform irrigation management with high resolution. Besides the work on remote sensing, we took advantage of the irrigation trial to determine the primary effects of sustained and regulated deficit irrigation on plant water status, berry composition, gas exchange, and yield components. There was little to no effect of irrigation treatment on plant performance and overall quality. The results of this study did follow the general trends for grapevines in semi-arid environments, although continued data acquisition is needed to assess the carry-over effect of water reduction on plants. As the drought conditions become more familiar to California grapevine growers, the need for effective water management solutions has heightened. Understanding the physiological responses of the plant at various intensities and timings can still provide great context for more advanced developments.
Summary: Warm, dry conditions can exacerbate late-season berry shrivel, reducing yield and altering berry sensory properties. Late-season shrivel occurs when the berries undergo programmed cell death, and the water released from the ruptured cells is drawn from the fruit to the canopy by a water potential gradient. The goal of our project was to test whether we could reduce shrivel by interrupting these processes. First, we tested whether short (2 week) pulses of increased irrigation before or at the expected onset of cell death would reduce water stress induced oxidative damage and delay or reduce the rate of programmed cell death, reducing shrivel at harvest. Second, we tested whether blocking the petiole water transport tissue (xylem) would reduce shrinkage by impeding water transport to the canopy. We implemented conventional (following standard commercial practices), early-pulse (before expected onset), and late-pulse (at expected onset) irrigation treatments on mature Cabernet Sauvignon vines in an experimental vineyard at UC Davis. We monitored vine water stress, berry cell death and shrivel, reactive oxygen species concentrations, markers for cell oxidative damage, and berry gene expression. We also used glue to partially block the pedicle for berries in the conventional irrigation treatment and compared diameter shrinkage to undamaged berries. The late irrigation treatment significantly reduced the rate of cell death and the magnitude of berry shrivel at harvest compared to the conventional treatment. However, the early irrigation treatment did not significantly impact cell death or shrivel. Concentrations of the reactive oxygen species H2O2 increased at the same time as cell death, consistent with a role in programmed cell death, but were not significantly different among treatments. We are still analyzing oxidative cell damage and berry transcriptomics, which we expect to provide more insight into the drivers of the treatment differences. Blocking the pedicle xylem did not significantly reduce shrinkage. Overall, these findings show that the time of onset of cell death is not impacted by water stress but using a short pulse of irrigation near the onset of cell death can slow the rate of cell death and reduce berry shrinkage at harvest.
Vine growth, yield, and fruit composition of Pinot noir grafted to 19 rootstocks and own-rooted vines were quantified during 2021. The vineyard was 24-years-old, and we hypothesized cumulative impacts of the rootstock on vine growth would be distinguished by rootstock. Specifically, we hypothesized that Riparia Gloire and other vigor-reducing rootstocks such as 101-14, 3309C, and 420A would have reduced canopy growth compared to other rootstocks not commonly planted in Oregon due to high vigor potential, such as 110R, 140R, 1103P, and 161- 49. Results show that the majority of rootstocks performed similarly for vine canopy growth and fruit production. However, there were some key differences noted. Dormant pruning weights in early 2021 indicate that Riparia Gloire, 44-53, and 3309C had the lowest pruning weights, indicating low vigor vines, and 161-49 and 1616 had the highest pruning weights, indicating high vigor vines. These differences carried into spring with differences in shoot growth from early may through bloom, with 3309C and Riparia Gloire having the least amount of shoot growth leading up to bloom, and 1616, 5BB, 140R, 5BB, 5CTE, and 420A having the most growth. There were some differences in fruitfulness, with SO4 having the greatest fruitfulness of 1.7 inflorescences/shoot while Riparia Gloire and own-rooted had only 1.4 inflorescences/shoot. There were yield differences by harvest, with 420A having higher yields than Riparia Gloire, 1616, and own-rooted. The impact on yield is mostly explained by differences in cluster weight. Pinot noir grafted to 1616, had the smallest clusters that were sparse due to poor set. This could be a result of high vigor of these vines early in the season. Berry ripeness did not differ for most rootstocks. However, Schwarzmann and Böerner had higher total soluble solids than 125AA. Schwarzmann also had the highest pH and lowest TA. The remaining rootstocks were all within commercially acceptable ripeness (TSS = 23.6, pH 3.2, and TA=8.6 g/L). We anticipated that variations in canopy size created by rootstock vigor may impact berry phenolics through vine stress and/or differences in canopy microclimate. However, there were no rootstock differences in total anthocyanin, phenolic, or tannin content. Similarly, there were no differences in berry phenolic concentrations in 2020. This second year of data analysis suggests that rootstock has the greatest impact on vegetative growth and yield, thereby causing some differences in vine balance. There is less impact on Pinot noir phenology advancement, fruit ripeness, or berry phenolic concentration at harvest.
This project reports the first six months of activity for this project. The goals are to develop predictive models to assess grape composition (total soluble solids, titratable acidity, anthocyanins) from hyperspectral imaging of berries and identify the most important wavelengths to foster the development of simplified sensors specifically adapted to monitor grapes in the field with reduced complexity and cost. It also plans to develop methods to deploy the sensors in the field, map grape composition on the go, and inform variable rate strategies to improve grape composition with spatially tailored canopy management techniques. We used the varietal collection at Fresno State to develop a spectral library of grape berries, including all commodities, wine grapes, table grapes, juice grapes, and raisins. We collected 496 samples from 77 black, red, and white varieties and nine sampling dates throughout the ripening. We imaged them with a VIS-NIR hyperspectral camera in controlled light conditions in the laboratory. We analyzed samples to measure °Brix, pH, titratable acidity, and the anthocyanin profile through HPLC. As planned, we are now developing machine-learning models to predict the sample composition. To field-test the system, we have identified two vineyards located in Madera and Fresno county and easy to reach from our campus. The vineyards show variability in grape composition at a short scale. We have been characterizing this variability with a randomized sampling based on the yield map at harvest. We have acquired imagery in the field and can segment clusters from grape canopies; we are now optimizing the sensing support system to obtain high-quality hyperspectral images in the field.
Adoption of sustainable soil management practices is becoming common in winegrape production in response to an increased awareness of the value of soil health to maintain environmental quality. Soil health is characterized by the functions it provides to the vineyard (i.e water retention, nutrient supply, carbon sequestration etc.) and is often impacted by vineyard floor management practices such as compost application, no till or the use of cover crops. However, the magnitude of the effect of healthy soil practices on soil organic matter and other soil health indicators is difficult to predict. A major impediment for the diagnosis and establishment of target values of soil health in vineyards is the large diversity of soils and physiographic conditions across and within growing regions. In this project, we carried out semi-structured interviews to growers paired with ongoing sampling efforts across 32 vineyards in Napa Valley to (i) establish a baseline of soil health indicators within the various Napa Valley soil types; and (ii) examine grower perception and comprehension of these indicators and the desired qualities of a healthy soil relative to production goals. Activities in this project were carried out though a collaboration between researchers, extension specialists and the Napa Valley Grapegrower Association. The data gathered so far shows that most grape growers consider soil health to be important for wine grape production due to perceived benefits to reduce soil erosion, improve vine health and grape quality. Through grower input, researchers were able to extract the soil properties that are the most important for these beneficial outcomes, namely a balanced soil structure and nutrient supply. Finally, data collected in the interviews revealed a strong grower knowledge of how the physical and chemical aspects of soil health are related to beneficial agronomic outcomes, as well as strong grower interest in understanding the role of soil organic matter and the soil biome on these outcomes. The research team is currently collecting soil samples to assess the variability and establish benchmarks for those soil health indicators that are desired for winegrape production. Furthermore, we will assess the role of soil organic matter and the soil microbiome with these indicators of soil health.
Proper management of salt accumulation in soils is crucial to prevent long-term reductions in productivity, especially where irrigation water is saline or sodic. Reclamation of saline-sodic soils requires the removal of most of the exchangeable Na+ and the replacement by Ca2+ in the root zone. One of the most effective practices to achieve this result is the use of chemical amendments containing calcium, such as calcium sulfate (CaSO4).
This project started in 2019 intending to compare different forms and doses of calcium sulfate and their effect on the physiology of grapevine growing in a sodic soil located in the southern San Joaquin Valley. The first year was devoted to locate the experimental site, perform a baseline of soil and plant conditions, and applying the treatments over 17 acres in a randomized complete block design with 6 treatments and 4 replications. In the second year, we monitored the soil conditions, plant physiology, and soil composition both on the ground and with the aid of satellite imagery and started to observe the first effects of the treatments.
(Year 1) Vine growth, yield, and fruit composition of Pinot noir grafted to 19 rootstocks and own-rooted vines were quantified during 2020. The vineyard was 23-years-old, and we hypothesized cumulative impacts of the rootstock on vine growth would be distinguished by rootstock. Specifically, we hypothesized that Riparia Gloire and other vigor-reducing rootstocks such as 101-14, 3309C, and 420A would have reduced canopy growth compared to other rootstocks not commonly planted in Oregon due to high vigor potential, such as 110R, 140R, 1103P, and 161- 49. Results show that the majority of rootstocks performed similarly for vine canopy growth and fruit production. However, there were some key differences noted in this first year of evaluation. Dormant pruning weights in early 2020 indicate that Riparia Gloire, 44-53, and 3309C had the lowest pruning weights, indicating low vigor vines, and 161-49 and 1616 had the highest pruning weights, indicating highly vigorous vines. Despite vigor differences noted during pruning, there were few to no differences in growth stage advancement at bud break, bloom, or fruit set. By the start of véraison Riparia Gloire and SO4 had the most advanced color development while 101- 14, 3309C, and own-rooted were the least advanced. However, within a 6 d window, the rootstocks became less different in percent of berries colored, and 3309C had the highest rate of color change. There were no differences in rootstock yield except for Riparia Gloire and SO4, which had the lowest and highest yields, respectively. Berry ripeness did not differ for most rootstocks. However, Schawarzmann had higher Brix than 420A, 5BB, 125AA, own-rooted, 5CTE and 99R. There were few differences in pH and variable differences in titratable acidity. We anticipated that variations in canopy size created by rootstock vigor may impact berry phenolics through vine stress and/or differences in canopy microclimate. However, there were no rootstock differences in total anthocyanin or phenolic content. There were minor differences in total tannins. We also anticipated that vine vigor conferred by rootstock may affect berry nitrogen, but there were few differences in juice primary amino N except for 1616 and 5BB that had more than double the primary amino N than 44-53 and own-rooted vines. This first year of data analysis suggests that rootstock has the greatest impact on vegetative growth and yield, thereby causing some differences in vine balance. There is less impact on Pinot noir phenological advancement, fruit ripeness, berry N or phenolics at harvest.
Soil moisture, weather data, and vine growth response were measured in 2020 in one vineyard location that had Pinot noir of the same vine age, clone and rootstock growing in three soil types, including volcanic soils (Saum), sedimentary soils (Dupee), and marine sediment soils (Willamette Woodburn). Soil sensors measured soil moisture, soil temperature, and electrical conductivity for each soil type. Soil probes were installed to a depth of 18 and 36 inches undervine and in the middle of the alley between rows. Soil moisture remained relatively consistent through much of spring, with the start of soil moisture decline beginning in mid-June. This occurred shortly after bloom, and continued throughout the rest of summer, when there was little to no precipitation. Vine growth measures of leaf area and lateral count did not vary in-season, but dormant season pruning weights show that the most vigorous vines grew in the WillametteWoodburn soil. Vine vegetative vigor was similar for Dupee and Saum. Soil moisture decline was greatest at the 18” depth and varied less at the 36” depth, and the greatest decline occurred with Willamette-Woodburn, suggesting that the higher vigor vines required more water from the soil profile than vines in the other two soil types. Leaf water potential did not show clear differences in vine water stress of the three soil types. Berry weight lagged slightly for Willamette-Woodburn, but there were no differences in the overall growth curve through development. By harvest, yields were similar from each soil type. However, the Willamette Woodburn had lower Brix and sugar per berry compared to the other two soil types. Data analysis from the 2020 season continues as of this reporting. This research will continue through two additional growing seasons (2021 and 2022).
Field trial, consisting of seven rootstocks, replicated in 3 times with 5 vines per experimental unit, was planted in 2015 at west side of Fresno County, and the scion variety of Pinot gris was field grafted in the spring of 2016. Data including soil/irrigation water salinity, tissue nutrients, yield components, harvest berry composition, and pruning weight were collected for the first (2017), the second (2018) and the third harvest (2019). Preliminary results from the three harvests have shown some interesting results among the rootstocks. Previously regarded salt-tolerant rootstocks for Cl, e.g., 1103P, 140Ru, Ramsey, performed as expected and our data were largely in line with previous results.
So far, rootstocks in our study had significant impact on plant nutrition, yield component and pruning weight, however, minimal effect on harvest fruit chemistry. Instead, vintage, especially irrigation water sources, played a crucial role in it. Interestingly, GRN 2 and 3 rootstocks which accumulated the most Cl, had the highest accumulative yields and pruning weight, although petiole Cl didn’t exceed the critical value. and this trial is still ongoing to collect more data to confirm the long-term impact. As for boron tolerance, GRN 3 rootstock showed the least amount of B uptake across three years. Correlation between juice Na and pH, berry size and B, have been found and it further validated the importance of rootstock selection, since rootstock might largely affect the fruit/wine chemical composition and yield.