Identifying the Potential to Use Vineyard Water Status to Alter Anthocyanins and Other Phenolic Compounds in Red Winegrapes

The first of two main objectives in this project is the separation and analysis of the phenolics present in approximately 300 fruit samples of Cabernet Sauvignon that were obtained from vines grown near Lodi and subjected to various irrigation regimes. The major phenolic compounds that change in concentration during ripening were identified by HPLC and comparison to standards. We identified approximately 20 compounds in skin extracts and juice samples that are of potential interest because of significant responses to changes in vine water status. These are categorized into phenolic classes, cinnamates, flavonols, and anthocyanins on the basis of their absorption spectra. For those compounds identified as present in significant concentrations, the seasonal pattern, the relationship of the concentration to the accumulation of sugars in the berry, and changes in these patterns caused well-defined differences in vine water status that were imposed before and after veraison were analyzed. The second specific objective was the establishment of a new field trial in a commercial Cabernet Sauvignon vineyard located in the North Coast. A field trial was established in a mature, uniform vineyard in Knight’s Valley on a light soil in which five irrigation regimes can be imposed that create early season water deficits and varying degrees of late season water deficits. The late ripening at the site will facilitate extended seasonal analysis of phenolic responses to vine water status.

Influence of Vine Trellis Training Systems on Growth, Yield, Fruit

The 1995 season represents the fourth season of this study. The experiment being conducted is a long term investigation of the influence of trellis/training systems on vine performance and the incidence of Eutypa dieback in a Cabernet Sauvignon vineyard. The goal of this experiment is to develop cultural practices which will reduce vine losses from Eutypa and reduce production costs without a reduction in yield or fruit quality. Results obtained in 1995 differed somewhat from results in the 1992-1994 seasons. This was in part due to the unusual environmental conditions which occurred during the 1995 growing season. Heavy spring rains and cool temperatures contributed to reduced early season growth and delayed canopy development. Unseasonable temperatures and wide fluctuations in temperature were experienced through most of the season. Minimally-pruned vines were skirted in June to reduce the crop level and facilitate cultural practices. Due to environmental conditions and crop level, harvest occurred much later (November 4) than in previous seasons. Yield was higher in 1995 than during 1992-1994 for hand-pruned treatments. As a result, there were no significant yield differences between the treatments. Significant differences were observed for components of yield. Vines which were minimally-pruned or machine-pruned had more clusters than hand-pruned vines. Berry weight, cluster weight, and berries/cluster displayed an inverse relationship with clusters/vine. Hand-pruned vines exhibited higher berry weight, cluster weight, and berries/cluster than minimally-pruned or machine-pruned vines. Trellis/training system had little effect on fruit composition in 1995. Vines which were minimally-pruned had more shoots per vine than vines receiving the other treatments. However, total vegetative growth was greatest for control (bilateral cordon) vines and was the lowest for minimally-pruned vines (mature nodes/vine). Symptoms of Eutypa infection were not observed in the plot during 1995. This result is not surprising in that symptoms of Eutypa usually first appear approximately 6-8 years after vineyard establishment. Therefore, treatment effects on Eutypa incidence should become evident in the next few years.

Interaction of Rootstock With Crop Load, Trellis System and Planting

This project proposed to investigate the interactions of rootstocks with cultural decisions such as pruning severity, trellis selection and spacing of vines within rows. The project was comprised of three experiments bearing on the interaction of rootstock with cultural practices. The three experiments were: Part A. Interaction of rootstock with crop load in Cabernet Sauvignon at the Oakville Experimental Vineyard. Part B. Interaction of rootstock with vine spacing on six trellis systems in Cabernet Sauvignon at the Oakville Experimental Vineyard. Part C. Interaction of rootstock with planting density in Chardonnay at the Beringer Hudson Ranch Vineyard. Data from Part A indicated that rootstocks reacted differentially to increasing bud number (cropping severity) at pruning. 039-16 was unable to ripen heavier crop loads as well as the other rootstocks. Increasing crop load for all rootstocks decreased all measures of growth. Data from Part B indicated that crop increased with canopy division whether that division was vertical (SH or TK2T) or horizontal (GDC, U and V), and that crop yield per acre increased as spacing between vines narrowed from 3 m to 2m to lm. Increase in yield for both factors was due to greater shoot numbers and cluster numbers per unit length row. In this case, 11 OR rootstock outyielded 039-16 by one ton per acre due primarily to greater numbers of shoots and clusters. Data from Part C indicated that the nine stocks could be divided into four vigor groups based on the amount of shoot growth as measured by shoot length, lateral and primary leaf areas and pruning weight. 039-16 and 420A were in classes by themselves as the highest and lowest vigor stocks, respectively. Between the two extremes, 1202, 110R, 5-C, 5BB, AXR exhibited intermediate growth while 3309 and 1616 tended toward low vigor. Shoot numbers did not vary, reflecting a constant bud number retained at pruning time but yields differed based on numbers of clusters/shoot. While crop loads per vine increased at wider spacing (due to more berries per cluster), the crop per acre was greatest at the higher planting density afforded by the 6 ft. Rows. Readers are encouraged to consult the Final Report for a complete analysis of the data.

New Parameters to Measure Ripeness

The HPLC method has not been used in a routine analytical fashion. This method uses cacao bean tannin extract for the determination of grape seed tannin molecular weight. Cacao bean extract contains procyanidin polymers consisting solely of epicatechin subunits which results in well separated, easily identifiable molecular weight markers. Since grape based tannins contain the same class of subunit, their retention characteristics are similar to cacao bean tannins. Quantification was achieved by comparing the peak areas of the grape extracts with that of an epicatechin standard. In order to apply this method in a routine fashion, additional method validation was performed and the reproducibility was determined. Based on the cacao bean extract, this method is capable of achieving a reproducibility of between 3.4%and 10%in the molecular weight range of 300-2100. Using this method, grape seed extracts have been analyzed. This method has the ability to quantify phenolics over a large molecular weight range, from 290 molecular weight units to about 3800 molecular weight units. This translates to a vast amount of information that can be obtained from extracts. From the vineyards studied this year, several trends can be seen in the extracts. First, the overall extractibility of the seeds decreases over time in both vineyards. Second, the amount of monomeric material extracted into solution decreased over time. Finally, the proportion of the extract which is made up of polymeric material (material having >6 subunits) increases as the grapes mature. Information on sample reproducibility was obtained using data gathered on all samples. In general, it was determined that the reproducibility was very good using the sampling technique used. In the worst case, berry weight and sugar reproducibility was 8.8%and 1.4%respectively. The reproducibility of grape seed extracts was determined also, and ranged form 3.9%for monomeric material to 27%for the polymeric material. Sensory analysis of wines made this year indicated that there was a significant increase (p=0.05) in astringency in both vineyards as the maturity of the grapes increased. When these wines were analyzed by HPLC, polymer concentration increased as astringency perception increased. Bitterness also increased in the wines as the grapes matured although the differences were much less significant. These results are inconsistent with the grape seed data, where the extractability of the seeds decreased as grapes matured. One possible explanation is that the high sugar levels in the grapes result in a higher alcohol concentration which can extract more tannin material from the seeds. Additional work is needed to study this possible relationship.

Optimal Viticultural Systems Comparison

The 1995 season represents the initial year of data collection for this project. Viticulture production system treatments continue to be established. Treatments included in the study are conventional, biologically intensive, and organic production systems. Production systems are being evaluated for effects on soil microbiology, viticultural and enological performance, populations of destructive and beneficial arthropods, and economic performance. Experimental protocols for sampling and analysis of soil microbiology in the study were developed during 1995. Soil samples collected in August and in October 1995 were analyzed for physical properties (water content, dry mass, and water holding capacity) as well as for chemical parameters (pH and total nitrogen). In the realm of microbiology, samples were analyzed for soil dehydrogenase activity, actinomycete enumeration, and microbial biomass. In addition, soil samples from all treatment plots were analyzed for plant parasitic nematodes. Soil microbiological analysis suggested high activity in the conventional treatment, intermediate activity in the conventional treatment, and low activity in the biologically intensive plots. It should be noted that this data is the result of the first season of data collection and is only preliminary. Plant parasitic nematode populations were quite low and did not appear to be influenced by production system. Nutritional status of vines was adequate and was not influenced by production system. Initial yield, fruit composition, wine quality and dormant pruning weight data will be collected during the 1997 season. Population patterns of important arthropods were monitored at approximately two week intervals from June through October. Population densities were low due to the fairly sparse canopy in the young vineyard. However, the following beneficial insect predators were detected; lady beetles (Coleoptera: Coccinellidae), green lacewings (Neuroptera: Chrysopidae), minute pirate bugs (Hemiptera. Anthocoridae), rove beetles (Coleoptera: Staphylinidae), and hover flies (Diptera: Syrphidae). These data are preliminary and continued development of the vineyard will enhance our ability to detect treatment differences.

Response of Chardonnay Grapevines to Windbreaks in the Salinas Valley

A five year (1991-1995) study examined the effects of windbreaks on the vegetative and reproductive growth of Chardonnay grapevines grown in the Salinas Valley of California. Vines enclosed in open-top chambers constructed of 50%density shade cloth were compared to vines grown under ambient conditions. Treatments were replicated eight times using seven vine plots. Wind speed within the shelters was reduced approximately 50%compared to ambient wind, while the temperature, relative humidity, and light environment of sheltered and non-sheltered were similar. Marked differences in vine growth and productivity were observed between the treatments. Sheltered vines had significantly larger primary and lateral leaves, greater total leaf area, and increased pruning weights compared to control vines. During periods of high velocity winds, sheltered vines had lower midday leaf water potentials, and greater stomatal conductances and net C02 assimilation rates, than control vines. Over the five year period, wind shelters increased vine yield 15%compared to the control. Yield improvements were due to increased cluster numbers per vine, as well as greater cluster weights as a result of more berries per cluster. Despite greater crop loads, fruit from sheltered vines reached maturity on the same time or slightly ahead of fruit from control vines. Treatments were harvested at similar soluble solids levels, however, fruit from sheltered vines had lower titratable acidity and higher pH compared to the control. Sensory analyses performed on wines produced in 1991 and 1992 indicated no preference between the treatments.

Water Use and Effects of Deficit Irrigation on Chardonnay

A study is being conducted to determine the water use or vineyard evapotranspiration (ET) of Chardonnay grapevines subsequent to vineyard establishment. ET is the combined loss of water by evaporation from the soil and transpiration by the vine. The experimental vineyard is located in the Carneros District of Napa Valley. In addition, the vines are grafted onto two different rootstocks (110R and 5C) to determine if there are differences in water use between them. Lastly, five irrigation treatments were imposed to determine the effects of both under- and over-irrigation on vine physiology and growth and wine quality. Vine water use is determined by measuring soil water depletion and the addition of water during an irrigation. Soil water content is being measured with a neutron probe at eight sites throughout the vineyard, four sites per rootstock. Vineyard water use in 1994 and 1995 at full ET (i.e. water applications equal to vine water use) were approximately 470 mm (18.5 inches). Deficit irrigation of vines resulted in the depletion of soil water, the amount dependent upon water application amounts. To date there has been no difference in water use between the two rootstocks. Water applications less than full ET result in more negative leaf water potentials and lower stomatal conductance and photosynthesis. The percent reduction is a function of the amount of water applied. There are highly significant correlations between the grapevine’s water status and soil water content when measured on the same day. There were significant reductions in berry size for vines that were deficit irrigated in 1994 but not in 1995. The difference between the years was due to an irrigation event in 1995 at berry set that resulted in no stress among treatments for a period of approximately three weeks. There has been no differences among irrigation treatments with regard to juice pH. Titratable acidity increased with increasing water applications both years. There were minor differences in berry composition among the rootstocks in 1995, however, there were no significant interactions among rootstocks and irrigation treatments. Experimental wines made in 1994 and 1995 are currently being analyzed. Preliminary results indicate a preference for wines made from the 75%and full ET irrigation treatments.

Wine Grape Canopy Management Practices in the San Joaquin Valley

This report concludes a study conducted in the San Joaquin Valley toward determining the most effective vine training and pruning system for fruit composition, quality, and yield while being cost-efficient and adaptable to mechanization. Previous work was conducted on training system and trellis designs and the effects of fruit exposure on yield and fruit composition. The current study compared pruning systems which can be mechanized and are much different in crop level, vegetative development, and canopy configuration. Six systems involving bilateral and quadrilateral cordon training and hand, machine-hedge, and minimal pruning were compared with French Colombard and Barbera. 1995 was the third year of a 3-year study. The treatments included: bilateral (Bilat) and quadrilateral (Quad) cordon training under both hand (Hand) and machine (Mach) pruning; and minimal pruning (Minimal Pruning/Cordon Training = MPCT) is also being compared with and without hedging to adjust crop load after fruit set (MPCT-Adjust). Generally, the treatments with the lowest pruning severity (MPCT, followed by MPCT-Adjust, Quad Mach, Bilat Mach, Quad Hand, and Bilat Hand) produced the most clusters of least weight. Thus, the vines tended to adjust crop loads with smaller clusters and berries. This resulted in comparable yields from all treatments except for lower fruit weights form the bilateral cordon pruning treatments and MPCT Adj. in French Colombard and the hand pruning treatments in Barbera. Thus, the most restrictive pruning level (hand) and vine canopy training (bilateral cordon) systems still tend to be the most limiting to yield. Fruit composition effects from treatment in French Colombard were minimal except for a 2-week or more delay in harvest from MPCT. The bilateral cordon systems, whether hand or machine pruned, were restrictive in overall yield potential. Also, there were no advantages in the MPCT system over quadrilateral training or machine pruning. Adjusting crop load after fruit set in MPCT did not respond favorably; it reduced yield while not improving fruit composition. Overall, the data indicate the greatest advantages with quadrilateral cordon training in this vigorous cultivar. Machine pruning also showed benefit in increasing yields in some years with no adverse effects on fruit ripening or composition. 38 Barbera was most responsive to machine pruning, with large yield increases over hand pruning. While there was some delay in fruit ripening (10-15 days) from machine pruning the berries reached comparable fruit composition on their respective harvest dates. MPCT pruning showed no improved yields over machine pruning and ripened later with lower berry skin anthocyanin. Additionally, MPCT Adj. did not show any benefits from crop load adjustment after fruit set. The hand-pruned systems produced some trade-off effects. While there was higher anthocyanin in Quad Hand fruit Bilat Hand resulted in the most bunch rot. Overall, quadrilateral cordon training was the most favorable system for French Colombard and with the advantage that it could be machine pruned without affecting fruit composition. Barbera responded favorably to quadrilateral training when hand pruned but the greatest yield increase was from machine pruning, although with some delayed fruit ripening (2 out of 3 years). The MPCT treatments have been disappointing. While they may reduce or eliminate pruning costs, fruit ripening was delayed by two weeks or more and with lower fruit anthocyanin (Barbera). Adjusting crop load in MPCT after fruit set is not producing favorable crop thinning effects. This is not surprising, as the supportive shoots and leaf canopy are removed with the clusters.

Wine Grape Canopy Management Practices in the San Joaquin Valley

This work is a continuation of studies conducted in the San Joaquin Valley toward determining the most effective canopy management practices for fruit composition, quality, and yield while being cost-efficient and adaptable to mechanization. Previous work was conducted on training system and trellis designs and the effects of fruit exposure on yield and fruit composition. The current study compares pruning systems which can be mechanized and are much different in crop level, vegetative development, and canopy configuration. Six systems involving bilateral and quadrilateral cordon training and hand, machine-hedge, and minimal pruning are being compared with French Colombard and Barbera. 1994 was the second year of a 3-year study. The treatments include: bilateral (Bilat) and quadrilateral (Quad) cordon training under both hand (Hand) and machine (Mach) pruning; and minimal pruning (Minimal Pruning/Cordon Training = MPCT) is also being compared with and without hedging to adjust crop load after fruit set. Generally, the treatments with the lowest pruning severity (MPCT, followed by MPCT-Adjust, Quad Mach, Bilat Mach, Quad Hand, and Bilat Hand) produced the most clusters of least weight. Thus, the vines tended to adjust crop loads with smaller clusters and berries. This resulted in comparable yields from all treatments except for lower fruit weights from the bilateral cordon pruning treatments and MPCT Adj. in French Colombard and the hand pruning treatments in Barbera. Thus, the most restrictive pruning level (hand) and vine canopy training (bilateral cordon) systems still tend to be the most limiting to yield and without any improvements in fruit maturation and composition. Fruit composition was not affected in French Colombard except for a 2-week or more delay in harvest from MPCT. The bilateral cordon systems, whether hand or machine pruned, have been restrictive in overall yield potential while there was no advantage in the MPCT over machine pruning. Adjusting crop load after fruit set in MPCT has not responded favorably; it reduces yield while not improving fruit composition. Overall, this second year of data indicates the greatest advantages with quadrilateral cordon training in this vigorous cultivar, especially with machine pruning. Barbera is responding favorably to machine pruning in the-second year of treatment by producing maximum yields with comparable fruit composition to the hand-pruned systems. Overall, the two machine pruning treatments « Bilat. Mach and Quad Mach ~ produced the highest yields with favorable fruit composition. MPCT pruning showed no improved yields over machine pruning and ripened later with lower berry skin anthocyanin. Additionally, MPCT Adj did not show any benefits from crop load adjustment after fruit set. The hand-pruned systems produced a trade-off, ie. higher anthocyanin in Quad Hand but higher bunch rot in Bilat Hand. To date, quadrilateral cordon training with machine pruning is most favorable for French Colombard. Barbera showed some delay in fruit maturation from machine pruning in the first year; machine pruning is now producing maximum yields without delayed ripening. The MPCT treatments have been disappointing. While they may reduce or eliminate pruning costs, fruit ripening is delayed by two weeks or more and with lower fruit anthocyanin (Barbera). Adjusting crop load in MPCT after fruit set is not producing favorable crop thinning effects. This is not surprising, as the supportive shoots and leaf canopy are removed with the clusters.

The Effect of Application and Timing of Cryolite on Fluoride Levels in Red and White Wines

The purpose of this experiment was to determine the level of fluoride in red and white wines from grapes sprayed with Cryolite at specific rates and application times. A five-year study conducted by CSU Fresno has conclusively shown that applications of Cryolite increase fluoride levels in red and white wines. From 1990 to 1994, different rates and timing combinations were tried in an effort to clarify the role of Cryolite in wine fluoride. In 1994, confirmation of a 6-pound full bloom rate was the basis for an application and timing trial tested on seven different vineyards in the northern, central, and southern San Joaquin Valley. Zinfandel, Barbera, Chardonnay, French Colombard, Muscat Canelli, and Thompson Seedless varieties were studied (Table 1). At CSU Fresno, a replicated experiment was performed on Thompson Seedless, Zinfandel, and French Colombard. The treatment schedule is listed in Table 2. Treatments were applied at each site using grower-supplied equipment. At Simpson Vineyards, because of a change in cultural practices, vines were sprayed with a backpack sprayer. At CSU Fresno, applications were made with a single row over-the-vine boom sprayer. Application dates for each site are shown in Table 3. Insect populations were monitored frequently during the growing season. No plots received applications of other non-fluoride containing products, but all other normal cultural practices were performed. Soil and water samples were taken from each site at the start of the experiment, and water samples were taken just prior to each application, to analyze for fluoride. Samples were analyzed by the Ion Selective Electrode (ISE) method. At harvest, grapes from each treatment were crushed, some juice kept aside, and the remainder made into wine. Grape juice was analyzed for fluoride by ISE., The wines were bottled and analyzed for fluoride by ISE. The water and soil fluoride levels are listed in Table 4. Water fluoride levels ranged from 0.04 to 0.48 ppm. Soil levels ranged from 0.59 to 1.73 ppm. Soil and water do not greatly influence the fluoride levels found in wines made from grapes sprayed with Cryolite, because the levels of fluoride in wines were not consistently higher to correspond with these water and soil levels. Both untreated control (Tl) juice and wine samples had less than 1 ppm fluoride. Wine and juice samples that received 6 pounds at bloom or pre-bloom (T3 or T4) had between 0.27 and 1.94 ppm fluoride. Applications at shatter (T5) had the highest fluoride levels, leading to the conclusion that later applications cause increased fluoride levels. Results of juice fluoride samples are listed in Table 5 and wine fluoride samples are listed in Table 6.