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.

Coupling Surface Renewal, The VSIM Model, Infrared Thermometry and Plant Water Stress Indicators to Optimize Water Application in Vineyards

Grape growers are in need of improved precision irrigation management tools that are cost effective and low labor intensive to manage both irrigation amount and timing of their crops. Multiple experiments were carried out to find alternative methods to measure grape water stress that could be couple with water use estimates obtained from surface renewal stations. These methods ranged from using single point IRT temperature measurements to fully automated station that measured surface temperature in real time. The primary objective of this year’s experiments was to determine if stress indices derived from less labor intensive methods such using VSIM and IRT models could be used as a replacement to the more costly and labor intensive commonly used by growers at this time.

Experiments were carried out in three locations. Ten surface renewal stations measured grape water use and water stress in J. Lohr vineyards located in Paso Robles. Leaf water potential measurements were made along with single point IRT canopy temperature measurements using a handheld IRT sensor. Stress indices derived from the handheld IRT temperature values had inconsistent degrees of relationship strength from one site to the next, when compared to leaf water potential values. There was no single stress index, IRT or surface renewal derived, that performed consistently better than the others across all sites. Two stationary stations measured continuous canopy temperature measurements on J. Lohr sites 11-2 and 1-2. Micrometeorological data was collected from reference evapotranspiration stations set up nearby. Stress indices derived from these two stations had strong relationships with the leaf water potential values that were measured.

Two more stationary stations making continual IRT surface temperature measurements were set up in collaboration with Terlato Wine Group over vineyards in the Napa and Pope valleys. Micrometeorological data collected from nearby weather stations were used along with the IRT surface temperatures to calculate stress indices. These stress indices had strong relationships with leaf water potential measurements.

A weather station was set up in the UC Davis Tyree teaching vineyard equipped with sensors to measure canopy temperature, windspeed, air temperature, incoming solar radiation, and relative humidity. Sensible heat flux values calculated using IRT surface temperatures and the surface renewal method had a strong relationship with sensible heat flux values calculated from eddy covariance. Canopy stomatal conductance calculated using IRT canopy temperature measurements had a strong relationship with leaf stomatal conductance values measured with a porometer and stress indices also showed high correlation with leaf water potential measurements made on the Cabernet grape vines.

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.

An Integrated Approach to Understanding How Grapevine Root Systems Respond To and Recover From Drought Stress

With our first year of funding from CGRIC, we made significant progress on this project and exciting new discoveries about grapevine fine root responses to drought that shed light on the differences among genotypes/rootstocks. The start date of the project was delayed by ~12months while we waited for the funds to become available, thus we couldn’t justify submitting a renewal in January 2016 for additional funds. We are now submitting a renewal to continue these efforts, which will cover the costs for the second year of the project. Our labs are continuing to work together closely on this and other related projects. In addition to the experimental results described below, we have collected and begun analyzing suberin responses using flurol yellow staining for the following 16 rootstocks/genotypes from a drought experiment run by Dr. Kevin Fort (Walker Lab)

Evaluation of New Winegrape Varieties for 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 tested were relatively recently released to the industry from Foundation Plant Services and had not been previously evaluated in California. All vines are on 1103P rootstock, trained to bilateral cordons, and most were spur pruned, leaving 8 to 10 two-bud spurs per meter of cordon. However, beginning in 2013, certain varieties have also been subjected to simulated mechanical pruning. Grapes were harvested according sugar accumulation, with the harvest target for white varieties at 22° Brix, and reds at 25° Brix. A few select varieties were picked at higher or lower Brix depending on a number of factors, including the desired wine style. At harvest, yield components, rot incidence, and basic juice chemistry were determined for all 56 varieties. As was typical in the region for 2015 and similar to 2014, the early ripening varieties were harvested earlier than in previous years. The first harvest occurred on 28 July 2015, and included Erbaluce, Petit Manseng, and Picolit. Fiano, typically the earliest variety harvested, followed soon after on 30 July 2015. Having failed to meet the desired Brix threshold for harvest, hand-pruned Parellada, Vernaccia Nera, and Counoise, and mechanically pruned Counoise, Caladoc, and Corvina Veronese, were harvested at the end of the season in early November. Total yields (inclusive of rot) ranged from 5.53 kg/vine (Carmenere) to 26.75 kg/vine (hand pruned Counoise). For the simulated mechanical pruning selections, yields were generally similar or greater than their hand pruned counterparts, with the exception of Counoise. Mechanical pruning either did not affect or reduced rot incidence for varieties harvested before October. But for the late ripening varieties, the late harvest required, probably due to overcropping in the mechanically pruned treatment, increased rot incidence in Corvina Veronese and Caladoc. Red and white varieties varied widely with respect to harvest date, pH, and titratable acidity. Twelve varieties which performed very poorly in the first two years of the trial were topworked to new selections in 2014 and used to make wine in 2015. From the work done in previous years, the most promising varieties were identified and, combined with the newly grafted varieties, a total of 23 selections were made into wine at Constellation Brand’s experimental winery and the finished wines will be evaluated and presented in the coming year. A selection of varieties that have been consistently poor performers with regards to rot and late ripening have been identified and are good candidates to be grafted over into more-promising selections in the future of this variety trial.