Evaluation of Ten Vitis vinifera cv. Pinot gris Clones in the San Joaquin Valley of California.

In June of 2017, 25 vines per Pinot gris clone from Foundation Plant Service, including FPS 01, 04, 05, 09, 10, 11, 52 and 08, grafted on Freedom rootstock as green potted vines, were planted at the commercial site located at Firebaugh, Fresno County, CA (36°45’22.2″N 120°28’12.6″W). Five vines of clone FPS 12, and ten vines, clone FPS 457, with the same rootstock were planted at the same date, due to lack of cuttings. Stakes with 24-inch horizontal cross arm and cordon wires, established to 54-inch height above vineyard floor, and irrigation tubing were installed after the planting. Irrigation and fertilization were carried out according to the vineyard cooperator based on the commercial industry standards for that area. Each experimental vine was flagged and labeled after the planting with the information of variety, rootstock, planting date and clone number on it. Vines were field checked regularly to assess the canopy growth, count the missing vines, and scout disease/pest. After the summer of 2017, extra vines with a total of 64 vines plus Freedom rootstocks have been ordered from Foundation Plant Service and cuttings will be collected in the dormant season of 2017. Cooperators from local nursery will help the grafting and prepare the green potted vines for replacing the missing vines in the field by the late spring of 2018.

In the fall of 2017, decision has been made to prune the vines back to two buds in the dormant period due to the non-uniform growth across vines. Therefore, vine trunk and cordon will be trained in 2018 and additional 64 vines will be planted to replace the missing vines in the late spring of 2018. The first harvest will be expected in 2019.

Determining the Impacts of Dormant Pruning Methods and Nitrogen Fertilization on Pinot Noir Bud Fruitfulness and Yield

This project is designed to provide scientifically tested information to growers about the impacts of two commercial management practices that can influence vineyard productivity: dormant pruning and nitrogen (N) fertilization. The Oregon industry uses primarily cane pruning for Pinot Noir, as they believe spur pruning will result in low yields (due to low bud fruitfulness) and reduce wine quality. Objective 1 of this study tests this question in a commercial vineyard, and we have been able to show with year 1 data that spur-pruned vines have fruitful basal buds, and that fruit composition and vine growth are equitable to that of cane-pruned vines. Although cluster size is smaller in spur-pruned vines, it was not enough to cause differences in whole vine yield. Results from our N-fertilization trial show little effect on bud and actual fruitfulness and yield after two seasons. Both experiments highlight the impact of vine vigor on bud fruitfulness, with greater fruitfulness observed with higher cane weights in the nitrogen trial and higher internode diameters in both pruning and fertilization trials. Additional years of this research will help determine the impacts of these management methods on yield potential over different seasons and vineyards to help growers adopt new pruning practices and/or enhance their vineyard N-management.

A Researcher-Industry Partnership to Understand the Yield-Quality Relationship in Cool Climate Pinot noir and Chardonnay Production

The long-term crop load study continued during 2017, the project’s sixth season. Eleven companies conducted the research on-site in 12 vineyards during 2017. Yields were the second highest in the six years of the study, second only to 2015. Average yield across all crop thinning treatments and sites was 1.13 lb/ft, which is higher than the 6-year mean of 0.93 lb/ft. Seasonal heat unit accumulation for 2017 was the lowest since 2012, and harvest was later than in recent years. However, fruit had sufficient ripening with total soluble solids (TSS) ranging from 21.0 – 25.0 °Brix. Analysis of harvest data across all sites in 2017 shows that fruit composition was affected by vineyard site and crop level. Treatment effects were tested within each vineyard site, and results show that only half of the sites (50%) had some treatment effect on fruit composition; however, the effects varied by site. There was no single fruit parameter that was affected by crop level at all sites, and the most common differences found by treatment were for TSS and pH in 2017. However, only 25% of vineyard sites had a difference in TSS with cluster thinning. Multiple regression analysis of data across the first five years (2012-2016) shows that crop load (yield: pruning weight, Y:PW) was related to TSS more than yield alone. Yield, however, was related to anthocyanin, pH and TA, with higher yields predicting lower pH, TA, anthocyanin, and tannin but higher TA. Fruit YAN was best predicted by pruning weights and Y:PW, not yield. Expert evaluation of wines from the 2012-2014 vintages show no yield effect on wine sensory perception, as wines did not group by yield level for descriptive analyses. According to industry collaborators surveyed, 43% had sufficient confidence in the study’s findings that they adopted higher yield targets in their vineyards beyond the research project, citing the ability to increase yield without compromising quality, and in recent warm years higher yields were preferred by winemakers.

Assessing Rootstock Biology and Water Uptake through Proximal Sensing under Different Wetting/Drying Conditions

Considering the importance of the water status as a driver of the whole plant physiology at the vineyard scale, developing new technologies for the space-time measurement of roots distribution and water uptake is crucial for the development of efficient precision viticulture practices. This project (2017-2022) is devoted to the development of a non-invasive technique (electrical resistivity tomography, ERT), as a tool to compare dynamic changes in root growth and water uptake patterns, and to apply this technique to the study of several commercially available rootstocks under varied irrigation delivery methods (drippers, micro-sprinklers) and water regimes (sustained deficit irrigation, rain fed, fully watered). The project was conducted in a vineyard at UC Davis specifically planted for the study of the response of rootstocks to watering systems. According to the timetable of the funded proposal the first year consisted of two parallel objectives: i) the calibration of ERT to soil water and roots distribution iii) the physiological monitoring of different rootstocks under different water amounts and delivery methods.

In a vineyard planted to Chardonnay on different rootstocks representing the most common parentage classes in a randomized complete block design, six soil pits were dug for the description of the soil profile, the sampling of the soil for chemical-physical analysis and the installation of TDR probes for the monitoring of soil moisture. The pits were then refilled, and the soil allowed to resettle for several months before the measurements commenced. The section of the field used for calibration purposes was not irrigated throughout the season in order to cover a full range of moisture levels for that soil (from 24% to 8% vol.). In close correspondence of these pits, at the soil surface 300 stainless steel electrodes were installed at a distance of 0.62 m (2 feet) for the ERT monitoring. A single ERT measurement was able to cover 2 plants on 2 different rootstock, which represented an experimental unit. The water status of the plants within the experimental units was monitored using infrared thermography and pressure chamber measurements. Photosynthesis and stomatal conductance were monitored through a pressure bomb. The electrical resistivity was calibrated to the soil water content obtained by TDR measurements, and two different pedoelectrical models were fitted to the data: Archie, in a canonical and linearized form, and Waxman and Smits models. Their performances were tested on 20% of the data from the whole dataset that were excluded from the model fitting and then used as a test set of unobserved data. The three modeling approaches gave similar results on the test set, with a slight decrease in performance from the log-log linearization (RMSE = 1.22% vol., R2 = 0.73) and the Archie law (1.22 %vol., R2 = 0.73), to the Waxman-Smits model (RMSE = 1.23% vol., R2 = 0.73). The Archie law was then chosen, and confirmed to be well adapted to predominantly sandy soils such as the experiment site. This calibration was used to transform the ERT images from soil resistivity to soil moisture maps under different rootstocks in 2D and 3D. This is the first report in the world that 3D images of soil moisture were developed in a vineyard, and the first time that this technique was used to compare rootstock physiology in general. Great differences were found between contiguous rootstocks in their spatial use of water. The presented data show how lateral heterogeneity in soil moisture could reduce the efficiency of spot measurements, as those obtained with soil probes, and soil moisture sensors in determining irrigation needs.

At the end of the season, the soil was sampled with an auger at different locations in the middle between contiguous ERT electrodes. The soil was sampled every 0.1 m, brought to the laboratory and oven-dried. Roots were physically separated from the soil, and their presence was assessed in a gravimetrically (mg of roots per g of soil). The presence of roots was negatively correlated to soil moisture obtained through ERT (r = 0.45), i.e. greater the amount of roots, lower the amount of water at the end of a dry period. This relations was then used to map the roots using ERT as ancillary variable for the spatialization, therefore developing the first electrical image of root distribution in a vineyard.

The Impacts of Cluster-Thinning and Cluster-Zone Leaf Removal on the Hormone Content of Pinot Noir Grape Berries

During the third year, we confirmed that the relative developmental stage of a berry was not fully a function of the flowering time, but was more associated with seed development. Therefore, our study reinforced the use of a new seed index (SI), also named SB or seed weight-to berry weight ratio to describe berry developmental stage. We have identified and optimized a selection method for selecting individual fruits of cluster at discrete stages using multivariate statistical tools in order to minimize inherent biological variability existing within a grape cluster. The analysis of bioactive forms of auxin, abscisic acid, cytokinin, brassinosteroid, gibberellin, jasmonic acid, and salicylic acid revealed a clear spatial and temporal distribution for most of them during the major critical steps of berry development.

Indeed, we were able to correlate the accumulation dynamics of most of them with major physiological events occurring during berry development. We were also successful in quantifying the effects of two common viticulture practices, cluster-thinning and cluster-zone leaf removal, on two major plant hormones responsible for the ripening initiation (ABA and Auxin). The analysis of the conjugate forms, precursors of, and catabolites of those bioactive analytes revealed specific regulatory pathways. These observations will lead to develop new working hypothesis to explain their mode of regulation in a tissue and developmental context. Based on our results, we will investigate in a near future other layers of biological information including gene expression. Encouraging results during the second year showing a peak ethylene during the ripening will need further investigation in order to prove the real contribution of endogenous ethylene production during grape berry development. From this study, we expect to have at least two peer-reviewed papers published as a result of this funded research and we will propose the results for oral presentation at the next conference of the American Society of Enology and Viticulture.

Evaluation of the Viticultural Performance of Newly Released Nematode Resistant Rootstocks in San Joaquin Valley Wine Grape Vineyards

As microscopic plant parasites, nematodes can cause extensive damage to grape vineyards. As the nematodes feed on and damage root cells, vine health, vigor, and productivity will decline. Nematodes affect many regions of California, but vineyards within the San Joaquin Valley (SJV) are particularly vulnerable to nematode damage due to typically sandy soil profiles and the wide range of parasitic nematode species found within the region, coupled with many soils being in agricultural production for decades. Traditionally, fumigation has been a viable method to provide relief from nematode pressur, but the California Department of Pesticide Regulation continues to regulate the volatile organic compound (VOC) emissions from field fumigants and fumigation is increasingly unavailable to growers with properties near schools or housing. Grape growers must begin to consider ways to reduce or eliminate the need to fumigate in order to keep up with regulations, but still ensure that nematode damage does not diminish the economic viability of their grape production. Rootstocks can provide a non-chemical alternative to resist soil pests like nematodes and maintain vine productivity. In recent years, several rootstocks have been released for commercial production including two USDA-ARS selections developed by David Ramming and Michael McKenry, RS-3 and RS-9, and the “GRN” series by Andrew Walker. Extensive work has examined nematode parasitism and sources of grape rootstock resistance, but how these rootstocks will perform with regards to viticultural characteristics in commercial plantings is still largely unknown. To promote the use of these new nematode resistant releases and see grape growers benefit from the years of research that went into developing these rootstocks, as well as be protected from increasing VOC emission regulation and economically damaging nematode pressure over time, field-based data on how these recent nematode resistant rootstock releases effect vine growth, yields, and fruit characteristics in commercial scale production is needed. In this study, on established trial site in a commercial high-wire, mechanically pruned Petit Verdot vineyard has consistently shown that Freedom generated the highest yields, but GRN4 also produces high yields. Freedom and the GRN selections generated significantly more growth than the comparatively weak performance of RS3, RS9, and 1103P at this site. 1103P was also under-ripe at the time of harvest, compared to the other selections. Seeing that several of the GRN selections were able to produce similar yields and fruit chemistry to Freedom, this indicates they may be a valuable tool for SJV grape growers to use when nematodes are a concern when planting. A second large-scale trial testing the GRN and RS selections was planted with Malbec in 2016, and will be evaluated as it matures. By using these two sites with a history of nematode pressure and managed under commercial growing conditions in non-fumigated fields, grape growers from around the SJV and all of California can benefit from the better understanding of how these rootstocks may effect vine vigor and berry maturation, and accordingly make the best choices to remain economically viable while using the best rootstocks available to resist nematodes.

Determine the Role of Auxin-Response Factor 4 in the Timing of Ripening Initiation in Vitis vinifera

Auxin-Response Factors (ARFs) together with Aux/IAA proteins mediate auxin responses including, floral development, fertilization, fruit set and development, and ripening process1. Among them, from our past research, the auxin response factor 4, VviARF4 a likely “key genetic regulator” during the onset of ripening2. The research project is proposed 1) to characterize the function of VviARF4 through genetic engineering, and to identify potential regulatory protein partners of ARF4* (see comments at the end of the document), 2) to determine the ripening-related genes targeted by VviARF4 during the onset of ripening, and 3) to evaluate the impact of altered expression of VviARF4 on the final fruit composition.

Since the commencement of the project in June 2016, significant efforts were made towards the objective 1. We first finalized the agreement for shipping the microvine lines with the USDA (See supplemental data). The signature of the Material Transfer Agreement is on its way between OSU and the CSIRO. Meanwhile, we concluded the logistics of the complex cloning strategies and finalized several vector constructs to transform the microvines designed to either turn on or turn off the activity of VviARF4 specifically during the fruit maturation stage. In the preliminary experiments, we are testing the gene silencing strategy in strawberry (Fragaria ananasa), which shows similar developmental pattern of ARF4 expression during the ripening initiation stage. The plasmid vectors designed to silence the endogenous FaARF4 and to over express the ARF4 from grapevine will into an aggressive Agrobacterium bacterium strain (EHA105).  We plan the transient transformation experiments in strawberry within three weeks from now. This will help to establish the role of ARF4 in another non-climacteric fruit model and will enable us to optimize our cloning strategy for the microvines.

The second part of the objective 1 is to find the regulatory protein partners of VviARF4 for which, we initiated the Yeast Two Hybrid Screens (Y2H). Through this approach, we expect to identify potential protein partners of VviARF4, which could have major regulatory role in VviARF4 gene function during the ripening initiation stage. We concluded the experiments to estimate the efficiency of library transformation in yeast and obtained satisfactory results. We are now preparing the final library in order to find the protein candidates that interact with ARF4.

Finally, as part of the objective 3, we are currently building our library of primary and secondary metabolites that will be analyzed when the microvines are transformed during the second year. The shipping of the microvines is expected by mid-February. Meanwhile, we are preparing the various media necessary to maintain the microvine calluses, to induce embryogenesis, to promote the regeneration, and to propagate the transformed materials. We anticipate being ready with the gene constructs cloned in to the Plant Gene Switch Vector to over-and under-express ARF4 before the microvine materials from CISRO, Australia arrive. The post-doctoral researcher is scheduled to fly to Australia in late March to get trained for the critical steps of the microvine transformation in collaboration with Dr. Thomas.


Evaluation of New Winegrape Varieties for Warm Climate Viticulture in the San Joaquin Valley

Fifty six different red and white wine grape selections are being evaluated at the Kearney Agricultural Center, in Parlier, CA. These varieties were originally selected because they originate from warm-climate Mediterranean regions, and/or were believed to have traits that would be desirable in a warm climate wine region, like the San Joaquin Valley. Most of the selections were recently released to the industry from Foundation Plant Services and had not been previously evaluated in San Joaquin Valley or California. All vines are on 1103P rootstock, trained to bilateral cordons, and most were spur pruned. Beginning in 2013, certain varieties have also been subjected to simulated mechanical pruning. In 2016, the effect of not shoot-thinning some select varieties was evaluated. Grapes were harvested according sugar accumulation, with the harvest target for white varieties at 22° Brix, and reds at 25° Brix. At harvest, yield components, rot incidence, and basic juice chemistry were determined for all 56 varieties. The first harvest was on August 3, 2016 for whites (Petit Manseng) and August 12, 2016 for the reds (Ederena, spur and mechanical pruning). Harvest dates were similar or slightly later than the historically early 2014 and 2015 seasons. Total yields were lower than previous years for almost every variety. Yields for the spur pruned, shoot-thinned standard treatment ranged from 6.54 kg/vine (Carmenere) to 32.14 kg/vine (St. Emillion). Given the repeatedly delayed ripening, poor color accumulation, and lack of adaptability to mechanical pruning, Caladoc, Corvina Veronese, and Counoise are not recommended for the SJV. Segalin, a darkly pigmented variety that looks promising, responded well when not shoot thinned in the spring, while the white varieties had a range of responses to the lack of shoot thinning. These differences in response to more minimal canopy management offer insight into how these varieties may need to be managed in a commercial setting. For the mimicked mechanical pruning selections, yields were only sometimes greater than their hand pruned counterparts, since the greater, smaller clusters also tended to exhibit worse raisining and have smaller berries that reduce yields. Red and white varieties varied widely with respect to harvest date, pH, and titratable acidity. Petit Manseng is the most acidic, which consistently measures >10g/L titratable acidity in this trial every year, but other high acid white varieties include Arinto, Falanghina, and Fiano. Clonal selections of Charbono and Teroldego were grafted in 2014 and used to make wine in 2016. Differences in rot incidence, and ripening are more predominate in the Charbono selections, whereas the Teroldego clones are more similar to one another. Among the reds, these clonal selections, Morastell, Sagrantino, and Segalin consistently produces reasonable yields under deficit irrigation while producing high levels of desirable color and flavor compounds. From the work done in previous years, the most promising varieties continue to be narrowed down and some were made into wine at Constellation Brand’s experimental winery and the UC Davis teaching winery, which provides enological information and valuable extension opportunities in the future. The final juice chemistry and finished wines will be evaluated and presented during 2017. Four new selections were grafted over into more-promising selections at the start of 2016 (Assyrtiko, Nero d’Avola, Grand Noir, and Petit Bouschet). Extensive extension and outreach efforts have been made to promote this work, including being published in trade magazines and local newspapers, giving extensions, and hosting an educational wine tasting and field day.

Comparing Nitrogen Fertilization in the Vineyard versus Supplementation in the Winery on Quality of Pinot noir and Chardonnay Wines and Productivity in the Vineyard

The overall goal of this project is to understand how nitrogen fertilization in the vineyard as compared to nitrogen supplementation in the winery affects wine properties in both a red and white cultivar. To achieve this goal, we are working in 2 vineyard blocks (Pinot noir and Chardonnay) each with a history of low nitrogen status, so that nitrogen can be added in the vineyard (to boost native must YAN) and also in the winery (to boost either ammonium-N or organic-N components of native YAN). Each variety trial has 4 treatments being evaluated using 4 replicates from the vineyard. The treatments are:

  • A) No N in vineyard + No N added in winery,
  • B) No N in vineyard + DAP in winery,
  • C) No N in vineyard + ORG-N in winery,
  • D) N Fertilized in vineyard.

The Pinot noir block was used for this trial beginning in 2015, but 2016 was the first year for Chardonnay. Unfortunately, the Pinot noir block was mistakenly tilled (alternate alleyways) by the vineyard crew in early April of 2016. We therefore, quickly replanted a grass cover crop in those alleyways, but the establishment was rather poor. The N fertilized treatment for both vineyards received 3 additions of 20 pounds per acre N, for a total of 60 pounds in 2016. We will likely reduce this to 40 pounds total in 2017, depending on results. The vineyard N addition in 2016 increased vine N status in both blocks, but the Chardonnay block responded faster and had a larger change than the Pinot noir block. The resulting must YAN levels were increased in N-fertilized vines by 38{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} in Pinot noir (from 176 to 243 NOPA YAN) and by 90{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} in Chardonnay (from 99 to 189 NOPA YAN). The vineyard N addition did not influence growth or yield of Pinot noir, nor growth of Chardonnay. The unfertilized treatment that was slated to receive organic N supplementation in the winery (treatment C) did have lower yield than the N-fertilized treatment in Chardonnay, but the other 2 treatments did not differ from the N-fertilized. Fruit solar exposure and vine water status were not altered by N fertilization in either variety in 2016. After winery additions to treatment B (+DAP) and C (+ORG-N), the N-fertilized and winery supplemented N treatments (B, C and D) had higher YAN than the Control (A) in Pinot noir. In Chardonnay, the + DAP (B) and N-fertilized (D) had the highest YAN, the + ORG-N (C) was lower than those 2 treatments, and the Control was lower still in YAN. The Pinot noir musts from N-fertilized vines fermented 1 day faster (significant at P < 0.05) than all other musts, even though YAN was just as high in the +DAP and +ORG-N musts. In Chardonnay, the Control musts with lowest YAN took about 2.5 more days to complete ferment than all other treatments, but this was not significant (P > 0.05). The sensory analysis of the 2016 wines will begin this summer.

Statewide Crop Load Project: A Researcher-Industry Partnership to Understand the Yield-Quality Relationship in Cool Climate Pinot noir and Chardonnay Production

The Statewide Crop Load project was conducted in 13 vineyard sites in 2016, including 12 Pinot noir vineyards and 1 Chardonnay vineyard. Results of the Pinot noir vineyards are reported here for data obtained as of this reporting and data are still pending from the Chardonnay vineyard. Yields during 2016 were down from 2014 and 2015, the highest yielding years of the project and were similar to yields obtained in 2013. Average yield across all crop thinning treatments and sites was 0.85 lb/ft in 2016 compared to the 5-year mean of 0.89 lb/ft. Heat units (GDD50) in 2016 were also lower than in 2014 and 2015, but harvest was earlier than the past four years with all harvest completed by the end of September. Fruit composition data indicates advanced ripening with total soluble solids ranging from 24.3 – 25.6°Brix for 2016. Analysis of fruit composition data across all sites in 2016 revealed that vineyard site, not crop level, led to differences in fruit composition. Treatment effects were tested within each vineyard site, and results show that the majority of sites (82{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}) had some treatment effect on fruit composition; however, the effects varied by site. No one fruit composition parameter was affected by crop level at all sites, and the most common differences found by treatment were for pH, titratable adidity, tartaric acid, and tannin in 2016. However, this effect was found at approximately one-third of vineyard sites. Furthermore, few crop level effects were found for anthocyanin content in 2016 while 15-28{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of sites from 2013-2015 had higher anthocyanin with lower crop levels. Further data analysis of vine growth, fruit composition and wine sensory is underway. Sensory evaluation has been expanded to include new in-house wine evaluation methods that were developed in 2016 for implementation in 2017. To capture industry-collaborator observations from the study to be used to enhance data interpretation and to develop yield management metrics, survey and interview tools were developed in 2016 and will be conducted in 2017. Updates on this project will be provided in future grant reports and outreach to the industry.