Comparison of Crop Load Management Systems and Differential Regulated Deficit Irrigation (RDI) on Vegetative Compensation, Whole-Canopy Photosynthesis, and Vine Performance in Procumbent Vitis vinifera L. in a Warm Climate

A traditionally managed head-trained, cane-pruned Merlot/Freedom vineyard planted on a California sprawl trellis was converted either to a bi-lateral cordon spur pruned (HP) or single high-wire bi-lateral cordon mechanically pruned (SHMP) crop load management system. Two irrigation treatments were applied. Vineyard was irrigated as follows A control treatment of sustained deficit irrigation (SDI) at 0.8 of estimated ETc was applied from anthesis until harvest (EL Stage 38) with a mid-day leaf water potential (¥[1]) threshold of -1.2 MPa. A regulated deficit irrigation (RDI) treatment was applied at 0.8 ETc from anthesis to fruit set (EL Stage 28) with a ¥[1]  threshold of -1.2 MPa, 0.5 ETc from fruit set to veraison (EL stage 35) with a ¥[1]  threshold of -1.4 MPa and at 0.8 ETc from veraison until harvest with a ¥[1]  at -1.2 MPa. Irrigation treatments were not initiated until ¥l reached -1.0MPa for vines in the 0.8 Etc treatments. It took one season to convert and establish canopies that can be cropped. In 2014 the  vineyard was cropped. The SHMP treatment irrigated with the SDI irrigation method generated the largest canopy earlier and was the most efficient user of applied water to fix carbohydrates. Furthermore, this canopy also yielded the greatest with acceptable canopy architecture and microclimate variables for the warm climate. There were few statistically significant effects of crop load management treatments or irrigation methods applied on seed and skin flavonoids. The total berry skin anthocyanins were most affected by the HP and SDI treatments in the initial year of data collection. The preliminary results suggest that it would take one full growing season to convert traditional California sprawl canopies to a SHMP trellis. The resultant canopy is a more efficient user of applied water amounts to fix carbon with greater yields with similar berry skin phenolics. The study is providing important science-based information for California wine[i] grape growers on how best to manage traditional California sprawl canopies to a SHMP trellis. The resultant canopy is a more efficient user of applied water amounts to fix carbon with greater yields with similar berry skin phenolics. The study is providing important science-based information for California wine grape growers on how best to manage traditional vineyards in times declining resources such as labor and water.

Interactive Effects of Mechanical Leaf Removal Timing and Regulated Deficit Irrigation on Biosynthesis of Methoxypyrazines and Phenolics on a Procumbent Grapevine (Vitis vinifera cv. Merlot) in the San Joaquin Valley of California

An experiment was conducted in the San Joaquin Valley of California on Merlot to determine the interaction of mechanical leaf removal (control, pre-bloom, post-fruit set) and applied water amounts [sustained deficit irrigation (SDI) at (0.8) and regulated deficit irrigation (RDI) at 0.8 (bud break-fruit set) – 0.5 (fruit set-veraison) – 0.8 (veraison-leaf fall) of estimated vineyard evapotranspiration (ETc) on productivity and berry skin anthocyanin content, composition and its unit cost per hectare.  The pre-bloom leaf removal treatment consistently maintained at least 20%of photosynthetically active radiation in the fruit zone in both years of the study, while post-fruit set leaf removal was inconsistent across years.  The RDI treatments reduced berry mass, while the post-fruit set leaf removal treatment reduced berry skin mass. The pre-bloom treatment did not affect yield in either year.  Exposed leaf area and leaf area to fruit ratio (m2/kg) were reduced with leaf removal treatments.  The RDI treatment consistently advanced Brix in juice.  Anthocyanin concentration was improved with pre-bloom leaf removal in both years while irrigation treatments had no effect.  Proportion of acylated and hydroxylated anthocyanins were not affected by leaf removal treatments.  In both years SDI increased di-hydroxylated anthocyanins while RDI increased tri-hydroxylated anthocyanins.  Pre-bloom leaf removal when combined with RDI maximized total skin anthocyanins (TSA) per hectare while no leaf removal and SDI produced the least. The cost to produce one unit of TSA was reduced 35%with the combination of pre-bloom leaf removal and RDI treatments when compared to no leaf removal and SDI.  This study provides information to red wine grape growers in warm regions on how to manage fruit to enhance anthocyanin concentration and proportion of anthocyanin hydroxylation while reducing input costs through mechanization and reduced irrigation.

The majority of wine grapes grown in the San Joaquin Valley (SJV) of California are used for bulk wine production.  Fruit used to make red wines from this region are characterized by low anthocyanin accumulation, and receive the lowest price per ton compared to other growing regions in the state. Approximately 34%of the Merlot grapes crushed in the state were grown in the SJV with an average grower return of $ 443/ton compared to $753/ton state average (Cal. Dept. Food. Agric. 2013).  In recent years more efforts have been directed towards applying principles of canopy management with the aid of vineyard mechanization and deficit irrigation practices (Kurtural et al. 2013; Terry and Kurtural 2011; Wessner and Kurtural 2013; Williams et al. 2012) to improve berry composition and grower returns per ton through enhancing the color profile of red wine grapes grown in the region.

Anthocyanins are synthesized via the flavonoid pathway in grapevine cultivars that harbor the wild-type VvmybA1 transcription factor for the expression of UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT) (Kobayashi et al. 2004).  The encoded enzyme UFGT catalyzes the glycosylation of unstable anthocyanidin aglycones into pigmented anthocyanins.  Two primary anthocyanins (cyanidin, delphinidin) are synthesized in the cytosol of the berry epidermis.  Cyanidin has a B-ring, di-hydroxylated at the 3’ and 4’ positions and delphinidin has a tri-hydroxylated B-ring because of an additional hydroxyl group at the 5’ position.  Flavonoid precursors are initially recruited from the phenylpropanoid pathway by chalcone synthases (CHS1, CHS2, and CHS3) and enter the flavonoid pathway.  Two parallel pathways downstream of flavonoid 3’-hydroxylase (F3’H) and flavonoid 3’,5’-hydroxylase (F3’5’H) (Castellarin et al. 2007) produce either cyanidin or delphinidin.  The 3’ position of cyanidin and delphinidin and sequentially the 5’ position of delphinidin are methoxylated by o-methyl-transferase (OMT) that generates peonidin, petunidin and malvidin, respectively (Castellarin et al. 2007).

The concentration and relative abundance of single and total anthocyanins are variable among red winegrape cultivars due to genetic control and developmental regulation.  However, there is general agreement in literature that when amount of diffuse light is increased (Dokoozlian and Kliewer 1995) or when an amelioration of microclimate temperature is associated with a concomitant increase in diffuse light quantity (Spayd et al. 2002), beneficial effects on total skin anthocyanin content of red wine grapes grown in hot climates are observed. Conversely, exposure of clusters to direct sunlight (Berqvist et al. 2001) or low sunlight with concomitant increase in berry temperature (Tarara et al. 2008) was shown to decrease anthocyanin accumulation, increase the proportion of 3’4’ hydroxylated anthocyanidins, and decrease the acylated anthocyanins contributing to total skin anthocyanins.  Cortell and Kennedy (2006) also reported a reduction of tri-hydroxylated anthocyanins in shade grown Pinot noir.  Therefore, the effect of sun exposure results from the interaction of several factors that are hardly uncoupled under vineyard conditions.

Leaf removal is a practice that can improve light transmittance into fruiting zone of the canopy (Diago et al. 2012; Poni et al. 2006; Wessner and Kurtural 2013; Williams 2012).  When leaf removal was applied pre-bloom it was shown to decrease berry set and hence grapevine yield, but improved total skin anthocyanin concentration of red wine grapes (Diago et al. 2012).  The results were used as a means of crop control with the increase in relative skin mass and reduction in yield per cluster being interpreted as the causal increase in anthocyanin concentration.  Therefore, since growers in SJV are paid in tons produced per hectare, previous work in the hot climate of SJV focused on post-fruit set, but was conducted pre-veraison in order to not adversely affect yield (Wessner and Kurtural 2013; Williams 2012). The leaf removal studies conducted in SJV resulted in improved photosynthetically active radiation exposure to canopy interior but no physiological gain for the cultivars studied, some deleterious effects were noted due to overexposure of clusters to direct solar radiation or vegetative compensation response (Geller and Kurtural 2012; Kurtural et al. 2013; Williams 2012).Water deficits were shown to consistently promote higher concentrations of anthocyanins in red wine grapes (Kennedy et al. 2002; Romero et al. 2010; Terry and Kurtural 2011).  However, there were conflicting results as to whether or not there were any direct effects on berry metabolism other than inhibition of berry growth.  It remained unclear if water deficits altered the biosynthetic pathway or if high anthocyanin concentrations resulted from elevated sensitivity of berry growth to water deficits.  Matthews and Anderson (1989) reported that growth of berries was inhibited more and concentrations of anthocyanin in berry skin and wine increased when water deficits were imposed before veraison rather than after veraison.  Similarly, Terry and Kurtural (2011) reported water deficits imposed one-week post-fruit set until veraison resulted in a 25%amelioration of total skin anthocyanins in central SJV.  Based on the observation of similar anthocyanin content per berry, Kennedy et al. (2002) and Terry and Kurtural (2011) concluded that post-veraison water deficits only inhibited fruit growth.

Gene expression studies investigating the regulation of anthocyanin biosynthesis in the grapevine concluded that both pre and post-veraison water deficits increased anthocyanin accumulation.  What is more, water deficits can progressively modify the canopy microclimate by defoliating the basal leaves subtending the fruiting zone, with greater exposure to solar radiation (Terry and Kurtural 2011; Williams 2012).  However, the increase in anthocyanin concentration observed in Merlot grapevines exposed to water deficits was determined not to be due to basal leaf defoliation and exposed solar radiation but was the direct result of water deficit.  Castellarin et al. (2007) reported that the increase in anthocyanin concentration in Merlot was not due to overexpression of FLS1 gene that is strongly correlated with cluster light exposure for flavonoid biosynthesis in the grapevine, but was due to up-regulation of flavonoid synthesis genes, in particular UFGT, CHS2, CHS3, and F3H.While canopy and crop load management studies (Geller and Kurtural 2012, Kurtural 2013; Terry and Kurtural 2011, Wessner and Kurtural 2013) and irrigation studies, particularly those implementing deficit irrigation, have been conducted in the coastal grape growing regions of California (Matthews and Anderson 1988; Williams 2010; 2014), no such studies have combined both factors on wine grapes cultivated in the hot climate of the SJV of California. The overachieving objective of this trial was to quantitatively increase the concentration of total skin anthocyanins of Merlot by investigating the interactive effects of manipulating solar radiation and water amounts applied in this hot climate. The specific objectives of the trial were to improve the light microclimate without adversely affecting yield components while simultaneously reducing applied water amounts to quantitatively and qualitatively improve the skin anthocyanin composition of Merlot in a resource limited environment.

The experiment was a three (leaf removal) × two (deficit irrigation) factorial with a split-plot design with four replicated blocks.  Three rows of 190 vines each comprised one block and four guard rows separated each block.  The three leaf removal treatments were randomly applied as main plot to three rows each.  Each main plot of three rows was split into two deficit irrigation treatments as sub-plot at random, in the geographic middle on the East-West axis of the vineyard.  Each experimental unit consisted of 285 vines of which 48 were sampled from an equi-distant grid per treatment-replicate.

 

 

 

 

Interaction of Rootstock, Mechanical Crop Load Management Systems and Differential Regulated Deficit Irrigation on Mineral Nutrient Requirements of Wine Grapes in Southern San Joaquin Valley

Grapevine leafroll disease causes non-uniform maturation of fruit in Vitis vinifera, including poor color development in red grape varieties. The disease causes losses of as much as 20-40%, with delays of 3 weeks to a month in fruit maturation. To date 5 different viruses, namely Grapevine leafroll associated virus (GLRaV) types -1 through -4, and -7, have been conclusively shown to be associated with leafroll disease. In the case of GLRaV-4, several distinct leafroll disease-associated virus strains have been identified within the virus species. This project was planned as a detailed study of the effects of these viruses on cultivar Cabernet Franc grapevines. This grapevine produces a readily scored foliar response to leafroll virus infection. The analysis includes challenges with each agromonically significant GLRaV species, including types -1 and -2 (2 isolates each), -3 (3 isolates), -4, -5, -7 and -9 (one isolate each). Also, pairwise combinations of GLRaVs -1, -2, -3, -5 and -7 are being tested. The test vines are grafted onto a broad selection of different rootstock varieties. Nine different rootstocks are involved in the test, including AXR #1, Mgt 101-14, 110R, 3309C, 5BB, 420A, Freedom, St.

George 15 and St. George 18. 15 replicates for each treatment are divided into three separate blocks each (5 replicate per treatment per block). The project has thus-far revealed a spectrum of differences in infection symptoms attributable to the different virus species, and to different combinations of these viruses and the grapevine varieties they infected. For example, it was observed that leaf symptoms produced by GLRaV-3 were more severe than those produced by GLRaV-4. In another example, it was found that GLRaV-2 induced more severe reactions on vines propagated specifically on rootstocks Freedom and 5BB. Those test vines exhibited red leaf symptoms, short internodes, and a near-lethal decline in vigor. Detailed analysis of these and other specific aspects of leafroll disease are on-going. In 2014, the vine performances were evaluated by measuring the trunk diameter, cane length, pruning weight, yield and fruit composition.

Trunk diameter analysis did not show much differences on each rootstock treated with different GLRaVs and virus isolates. For cane length measurements, the data showed that St. George 15 and St. George 18 rootstocks were not affected by different treatments. However, the two different isolates of GLRaV-2 (2B and 2C) had significant impact on cane length of plants propagated on rootstocks 101-14, 3309C, 5BB and Freedom. The yield did not show any significant difference between different treatments on rootstocks 110R, 420A, 5BB, AXR, Freedom, St. George 15 and -18. Pruning weight analysis did not show any differences between different treatments and rootstocks 110R, 420A, St. George 15 and -18. However, significant differences were observed between different treatments and the rootstocks 101-14, 3309C, 5BB and Freedom. Rootstock AXR was less affected. The analysis also showed that both GLRaV-2 isolates (2B and 2C) in general have been more severely affected the plants on panel of rootstocks.

Defining Crop Load Metrics for Quality Pinot Noir Production in Oregon

A three year study began in 2013 to determine the impact of varying crop levels on vine growth and balance. The project involves two components: 1) a large grower collaborator crop load study and 2) a study that monitors vine growth, nutrition and physiology measures within four sites from the larger study. A total of 13 vineyard and winery collaborators have participated in the research and completed two full growing seasons of data collection and wine production for the study in 2013 and 2014. The 2013 season results from the large grower collaborative study indicates few differences in vine size (pruning weight), vine nutrient status, or fruit composition at harvest. Data from for the 2014 season are still being gathered from collaborators and will be analyzed statistically in spring/summer 2015. Data obtained from the four detail sites during 2013 and 2014 show no difference in vine nutrition at bloom or véraison, vine photoassimilation rates, nor differences in vine growth and leaf area when comparing full crop (non-thinned vines) with those cluster-thinned to one cluster/shoot. Despite very high yields in 2014, cluster thinning did not drastically change ripeness parameters measured. The differences in vine productivity among sites within the two projects are valuable in understanding how crop load may be influencing fruit composition and quality in vineyards with different yield capacity. The data obtained from the first two years of this research suggests that the Pinot noir vines in the Willamette Valley of Oregon may reach vine balance on their own and do not require cluster thinning to adjust for fruit ripeness or to maintain vine growth. Further seasons of research are required to better understand the role of vine balance.

Impact of Vine Vigor, Nitrogen, and Carbohydrate Status on Fruitfulness of Pinot Noir

The first year of a two-year research project was completed in 2014. The project involves three components, all analyzed within main plot vines managed with different vineyard floor management practices and different levels of vine vigor and nitrogen status. Preliminary results show that bud fruitfulness is not reduced at basal nodes for canes assessed within any of the vineyard floor treatments. Vines grown with cultivated alleyways (Tilled) were the most vigorous with the greatest leaf area and lowest light infiltration compared to vines with grass alleyways (Grass). Dormant buds collected in winter 2014 from Tilled treatment vines had the highest fruitfulness at several nodes along the cane. Primary bud necrosis was rarely found and did not differ between Tilled and Grass treatments. Grass vines had less leaf area, lower yields and higher fruit total soluble solids at harvest as was found in prior years of research in this block. Vine tissue N and carbohydrate analysis are still pending as of this reporting. The differences in nitrogen (%N) and total non-structural carbohydrates of bud, cane, shoot, trunk and root samples will be compared to bud fruitfulness data to understand the dynamic role of N and carbohydrates on bud development and fruitfulness. Within the main plot vineyard floor management study, two experiments were conducted within sub-plots to evaluate the effect of canopy management practices on bud fruitfulness, including lateral removal and cluster zone leaf removal. Both included a time course study of lateral and leaf removal.

Lateral shoot removal treatments were imposed during one of three different time points (fruit set, pea-size and bunch closure) in 2014 and compared to a no lateral removal treatment. Timing of lateral removal did not increase light exposure to the upper canopy where laterals were removed, indicating that any differences in bud fruitfulness within apical sections of dormant canes may be due to internal differences such as nitrogen or carbohydrates rather than light or temperature effects. The main differences in canopy light were due to the main plot effect (Grass, Alternate and Tilled). There were no differences in photoassimilation rates of primary leaves with or without a lateral. Data collected from these experiments will be compared with bud fruitfulness that is currently being assessed for winter 2015. Cluster zone leaf removal was applied to vines during one of three different time points during 2014 (bloom, fruit set, and pea-size), and these were compared to a no leaf removal treatment. Leaf removal increased light exposure to the buds in the fruit zone where leaves were pulled. Within the Grass vines, yields were higher with no leaf removal compared to those with leaf removal. Grass vines had lower total vine leaf area than Alternate and Tilled vines, and removal of leaves early season could have affected fruit set. Fruit set data are still being analyzed. Data collected from these experiments will be compared with bud fruitfulness that is currently being assessed for winter 2015.

Mitigation of Vineyard Greenhouse Gas Production Using Organic Floor Management

Since April 2013, this study has closely monitored the effects of organic floor fertility strategies (leguminous cover crops, grape pomace composted with manure) in concert with soil carbon storage techniques (biochar and grape pomace compost) Gathered annually are a number of soil, vine, and grape metrics at the University of California Oakville Station. Preliminary effects of these treatments on soil greenhouse gas emissions (nitrous oxide, carbon dioxide, and methane), plant available nitrogen (ammonium and nitrate), soil moisture, vine vigor, and berry quality were discerned. Perhaps the most important results acquired thus far are the monthly trends and magnitude of soil nitrous oxide (N2O) emissions and mineral N availability. Nitrous oxide is a GHG with 300 times the global warming potential of carbon dioxide (CO2), therefore causing significant potential carbon offsets, and limited N fertility was found to severely restrict harvest yields during the decade preceding this investigation. Periods of large N2O production were largely initiated by substantial rain events. When cover cropped or compost supplemented soils were amended with biochar, significant reductions in N2O were observed compared to organically fertilized controls during individual rain periods. However, when organic N fertilizer was not present, biochar-only plots emitted significantly more N2O than conventional controls. There was little difference throughout the year in plant available nitrogen as ammonium (NH4-N) among all treatments, yet a striking contrast in plant available nitrogen as nitrate (NO3-N). Yields have been restored to ca 4+ tons per acre and although yields for the non-conventional treatments were significantly higher in 2013, they did not differ from conventionally fertilized plots in 2014. Thus, this study demonstrates that organic ground fertilizations used in concert with biochar amendments can increase NO3-N provisions while maintaining NH4-N and decreasing vineyard scale N2O emissions.

No significant changes in carbon leaving the soil as CO2 or methane (CH4), were detected on an annual basis. In yearly assessments of total carbon, we were able to determine that both biochar and grape pomace compost did appreciably increase soil carbon content compared to conventional controls upon application. However, we found that the effect of these treatments on annual increases in carbon were negligible but the study will need to continue over years to discern long-term effects.

Vineyard Air Temperature Profiles and Their Implications for Vine Training Decisions

This project evaluated how air temperatures vary with height above the ground surface throughout the growing season at various vineyard areas representative of the diverse Central Coast region. The purpose of this project was to identify if useful stratification in temperatures occurred at the study sites, and to quantify the potential benefits that could be attained by using alternative vine training heights to reduce potential frost risk and/or to avoid excessive summertime temperatures. The fundamental hypothesis of this effort has been that taller vine training heights may bring useful benefits in some areas, and that this type of detailed temperature analysis will help identify those areas and help to predict what benefits may be obtained with any changes in vine training height.

The 2013 season measurements at seven sites in San Luis Obispo and Santa Barbara Counties proceeded as planned, however with an equipment malfunction resulting in only partial season data at one site in Shandon. Temperatures were measured at one-foot intervals above the ground surface between 1 ft. and 8 ft. heights, using precision data loggers taking high-frequency measurements. Some sites demonstrated useful increases in temperature with increasing height above the ground surface on cold spring nights, but this pattern was not observed everywhere. In the most extreme example, the temperature gain at 8 ft. elevation was 9 °F warmer than at 1 ft. elevation; such stratification would have very positive benefits for frost protection. Other sites showed little similar stratification, likely due to air movement during the night.

At all sites the cumulative degree days over the April 1 – October 31 growing period tended to decrease with increasing height above the ground. This indicates the potential that taller vine training heights may have for addressing some of the gradual increases in degree days that have been occurring in recent decades, and which are forecast to continue increasing with climate change.

In 2014, detailed measurements are being conducted with multiple stations at two properties, to determine how variable the temperature profile characteristics can be at individual sites. The assessment of temperature profiles over different ground cover conditions was not conducted as planned due to insufficient cover crop conditions; this will be addressed at a later date.

Evaluation of new Winegrape Varieties for the San Joaquin Valley

A wine grape variety trial was established in 2008 at the Kearney Research and Extension Center, a warm climate region. The trial consists of 55 16-vine plots, each planted to a different red or white wine grape selection originating from warm-climate Mediterranean regions, and/or believed to have traits that would be desirable in a warm climate wine region. Most of the selections tested were recently released to the industry from Foundation Plant Services so, in many cases, certified selections have never been evaluated in California. All vines are on 1103P rootstock and in 2011 and 2012, the first two cropping years, all vines were spur pruned, leaving 8 or 9 two-bud spurs per meter of cordon; in 2013, certain varieties were subjected to simulated machine pruning, or cane pruning.

In general, we attempted to harvest all white varieties at 22 Brix, and reds at 24 Brix, but certain selections 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 chemistry were determined and wine lots were made at Constellation Brand’s experimental winery. The varieties were harvested across a wide range of dates starting with a white cultivar, Fiano, in early August, and ending with about a half dozen red and white varieties that were harvested on the last day of October. Yields ranged from less than 6 kg per vine for Prieto Picudo to more than 50 kg of fruit per vine from the machine-pruned Tocai fruliano, a white cultivar. Red and white varieties varied widely with respect to harvest date, pH, and titratable acidity. Berries from red varieties also varied widely in their content of anthocyanins, tannins, and other phenolic compounds.

Most varieties had slightly higher anthocyanin content in 2013 than they did in 2012, and Bonarda and Segalin noir have consistently had the highest anthocyanin content of the varieties tested. Wines from the trial will be made available for tasting and analysis in 2014, as they have been in each of the past several years. Twelve varieties which performed very poorly in 2011 and 2012 were topworked to new selections in 2013, and some varieties were subjected to different canopy management practices to determine if yield and rot problems could be ameliorated. Shoot tucking generally had little if any affect on fruit quality or rot, but simulated machine pruning greatly increased yields and reduced rot of most varieties subjected to this practice. Additional years of data are needed to determine if the high yields of machine-pruned vines are sustainable and whether or not they adversely affect fruit or wine quality.

Defining Crop Load Metrics for Quality Pinot Noir Production in Oregon

A three year study began in 2013 to determine the impact of varying crop levels on vine growth and vine balance. The project involves two components: 1) development of a large grower collaborator crop load study and 2) monitoring of vine growth, nutrition and physiology measures within four sites from the larger study. During 2013, the project included a total of 13 vineyard and winery businesses from across six AVAs in the Willamette Valley of Oregon. Collaborators successfully completed their first season of data collection as of this reporting, and results are being compiled and analyzed in winter 2014. The additional data from the four sites within the study are being analyzed in winter 2014, but preliminary data that shows no difference in vine photosynethetic assimilation or vine nutrition at bloom or véraison when comparing full crop (non-thinned vines) with those thinned to one cluster/shoot.

Water Footprint, Productivity and Drought Responses of Seventeen Wine grape Cultivars in the San Joaquin Valley

This research focuses on the adaptation and drought responses in yield and fruit and wine quality of seventeen, red wine grape cultivars. The project exploits an established variety trial in which the cultivars were selected for potential adaptation to San Joaquin Valley conditions and by doing so extend the information derived from the previous investment to establish this experimental vineyard – used by Dr. Jim Wolpert from 2006 to 2010. Reducing the plant-available water (by restricting irrigation) can be expected to reduce yield, but to also increase water use efficiency and fruit quality of red wine grapes. The timing of water deficits affects many of the vine responses to stress and the resulting wine sensory characteristics. For example, early(preveraison) deficits have a greater effect on tannins than late deficits, whereas for anthocyanins(color) it is the reverse. The studies that have established these phenomena were conducted in moderate (North Coast) climates and with common cultivars such as Merlot, Cabernet Sauvignon and Cabernet franc. This study will test whether those observations hold in the warmer San Joaquin Valley across numerous cultivars.

Estimated ETc from budbreak to average date of harvest across cultivars and irrigation treatments (end of August) was 619 mm (24.4 in). Applied water to vines irrigated at full ET from budbreak  to veraison after which the irrigation was terminated (I ? Ni treatment), applied water at 50%of estimated ETc season long (0.5 ETc treatment) and no applied water up to veraison and then applications thereafter at 50%of ETc (Ni ? 0.5) were 397, 347 – 453 and 173 – 293 mm,  respectively. The effect of irrigation treatment on vine water status (midday leaf water potential) similarly affected all cultivars.

Early water deficits (no applied water up to veraison; Ni ? 0.5 treatment) greatly reduced berry weight at veraison and harvest compared to the other two irrigation treatments across cultivars. The no applied water after veraison treatment (I ? Ni) reduced berry weight of 13 cultivars at harvest compared to their veraison berry weight. Titratable acidity (TA) in the berries of 15 of the cultivars at harvest was greater for the I ? Ni treatment compared to the other two irrigation treatments (the exceptions were Tinta Amarella and Tinta Madeira). The greatest TA values across irrigation treatments were for Durif, Cabernet Sauvignon and Tannat. Berries and the wines made last year are currently being analyzed for color, phenols and tannins.