Cultural Practices to Modify Berry Physical Properties and Susceptibility to Cracking

Ethrel sprays, irrigation regimes, and girdling all had a significant influence on Flame Seedless cracking in the 2010 field trials at Arvin, CA. Among the 64 treatment combinations of these factors, ethrel sprays had the largest effects, particularly the first ethrel spray, which increased cracking rate by six-fold compared to plots with no spray. This suggests that the dose and timing of the ethrel spray may be a key issue in balancing the advantages for color development with disadvantages of cracking. The four irrigation treatments, 0.6X, 1X (grower standard), 1.7X and 2.3X, caused clear differences in plant water status as measured by stem water potential (SWP), with berries from the higher irrigation treatments having significantly increased berry size, but also increased cracking, and berries from the lowest irrigation having decreased size, firmness, and cracking. Cell turgor was also well correlated with berry firmness. The correlation between irrigation and cracking justifies the prospect of future usage of SWP and other linked berry properties to monitor and minimize cracking, and we will continue research to resolve these factors in order to provide growers with information about threshold values for cracking. Girdling also significantly increased cracking with the late girdle having higher effects than the early girdle. Late girdle may not be as necessary for this field considering its negative impact on cracking but minor effects on color development.

Tracking of individual berry growth showed that berries at around veraison expanded with an average rate of about 2.5% per day, but most of the expansion occurred at night. A peak short-term rate equivalent to 6.4-8.5% per day was exhibited at 7-8am, but the monitored berries that showed these rates did not crack. Skin mechanical properties in the standard and frequent irrigation treatments were tested with custom equipment (berry balloon system, BBS), and in both treatments, pressure, stress and skin strain at failure (cracking) progressively decreased over berry development, indicating, as expected, that cracking susceptibility increases over time. In the scanning electron microscope (SEM) the surfaces of field-cracked, soaking-cracked, and BBS-cracked berries all showed clear evidence of failure by cell wall breaking and not cell separation, contrary to current scientific thinking. The BBS also detected varietal differences (Flame seedless vs Syrah) in skin mechanical properties, and given the strong impacts of ethrel spray on cracking, it will be important to quantify skin properties with BBS for the different ethrel treatments in 2011. Flame seedless berries were soaked in water with only the stylar end or the longitudinal side immersed, and berries cracked at the stylar end in the former case but remained intact in the latter. Soaking of entire flame seedless berries in water confirmed that berries crack at a fairly low strain (<5%). These results and our SEM images showing broken cell walls, indicate that cracking is most likely a local event that is initiated by failure of a few cells rather than a consequence of an overall expansion of the flesh, as previously believed.

The Determination of Crop Coefficients for Central Coast Vineyards

This project has further developed and applied a novel method for determining the site-specific irrigation crop coefficient, based on measurements of the midday canopy shaded areas using large solar panels. The canopy shaded areas were measured at eight vineyards throughout the growing season in San Luis Obispo County, and converted to crop coefficients. Together with local reference evapotranspiration and irrigation application data, the irrigation applications were expressed as a percentage of the full potential vine water use.

This technique makes it truly practical to fully utilize the equation developed by Williams and Ayers, which correlates the midday canopy shaded area to the irrigation crop coefficient. Prior to the development of this solar-panel method, the use of this equation was largely limited to research purposes, as the effort required for measuring the canopy shaded area using the existing manual or photographic techniques was impractical for commercial operations. The site-specific crop coefficients that a grower can collect with this method will allow one to apply climate-based irrigation scheduling with more confidence, less risk, and more consistency season after season. The large differences between the crop coefficients measured at sites that had similar trellis systems indicate that there is a value in measuring these coefficients locally.

With accurate crop coefficients it becomes possible to perform detailed evaluations of irrigation management at a given site, quantifying the season?s irrigation applications as percentages of the full potential vine water use. These results show, likely for the first time, just what degree of irrigation deficit the test plot vines were subjected to during the growing season.

Inception, Diagnosis, and Consequences of the Berry Shrivel Disorder

Berry shrivel (BS) is a disorder of unknown cause and sporadic appearance that has been increasingly observed in vineyards in Napa and Sonoma Counties. BS is commonly misdiagnosed as bunch stem necrosis (BSN), but we have found that the disorders can be clearly distinguished based on the presence of a healthy, green rachis in BS compared to a necrotic rachis in BSN-affected clusters, and the fact that BSN berries have normal to high Brix whereas BS berries have much lower Brix than normal berries. This was the second year of our study of BS development, and the first in which BS was prevalent enough to obtain a representative sample of BS berries over time. In order to determine whether BS is a berry, cluster, or vine level phenomenon, a substantial amount of over-sampling was required, and hence not all the 2005 samples of berry composition have been analyzed to date.

In both 2004 and 2005, around the time of veraison, and prior to any appearance of BS symptoms, BS berries were firmer than control berries, but the decline in firmness at veraison was faster in BS than in control berries, so that for most of the post-veraison period, BS berries were softer than controls. In 2004, BS fruit skin had a slightly increased mass of cell wall material compared to the skin of control berries, and a slightly reduced amount of cell wall material in the mesocarp, indicating that the disorder may be related to metabolic aberrations in cell wall metabolism in the mesocarp. In 2005, with a larger sample size, this was not the case. It is also unclear to what extent BS is associated with water stress. In Oakville, vines which historically have exhibited BS have been consistently less stressed than controls, but the opposite trend was observed in Sonoma County, and in nether location was the degree of BS associated with the level of water stress, as measured by leaf water potential.

In both 2004 and 2005, visual symptoms of shriveling, whether caused by BS, cluster girdling, or cluster excision, were always associated with a loss in mesocarp cell viability (as indicated by a fluorescent vital stain), and hence we can attribute the shriveling to cell death, rather than simply to berry desiccation. In both years there has been no apparent difference between BS and control berries in the xylem connection between the berry and the pedicle. For the 2005 berry composition data that is available, BS berries were similar to berries on girdled clusters, in that they both accumulated less soluble solids and had a lower pH than control berries. One key result from 2005 is that there is also evidence that BS symptoms, as measured by essentially all of the major indicators of berry development (Brix, pH, dry weight), are progressive over the season and are also expressed at the whole-vine level. Berries that show early symptoms of BS are the most affected, but lesser degrees of symptoms also occur in berries that are affected late, and still lesser, but measurable, symptoms occur on apparently healthy berries from affected vines. These results strongly suggest that, for a vineyard that is affected by the BS disorder, the effects of the disorder may not be limited only to clusters exhibiting shriveled berries.

Our current hypothesis is that BS is not a disorder related to xylem function and vine water relations, as thought previously, but rather a disorder either of phloem function and/or of vine photosynthesis. Wines were made from commercial Cabernet fruit (BV vineyard in Rutherford) that was either free from BS, or had varying levels of BS (5, 10, or 15%by weight), or BSN (40%by weight) fruit. In all cases, fermentation proceeded normally, and these wines will be subject to sensory and chemical analysis.

Effects of Berry Size and Crop Yield on Wine Composition and Sensory Quality

The effects of vine irrigation and crop yield on sensory quality of Cabernet Sauvignon wine from the 2000 harvest were investigated using descriptive analysis with a trained panel, quality ratings by members of the wine industry and tannin assays.Wines produced from vines with low irrigation regimes were rated highest in dried fruit/raisin, jam, and red/black berry aromas, fruity by mouth, and acidity and lowest in brown color. The high irrigation wines were rated lowest in bitterness, ethanol, body, and darkness. The medium irrigation wines were ranked highest in veggie aroma, astringency, brown, dark, body, ethanol, and bitterness and were ranked lowest in cherry aroma. Low irrigation wines received slightly higher quality ratings from members of the wine industry than high irrigation wines, but the difference was not significant, possibly because of differences among wine replicates.Lower crop yields tended to produce wines with high bell pepper and black pepper aromas, high astringency and bitterness, and high ethanol and veggie by mouth flavors, whereas the higher yields tended to result in wines with higher red/black berry, jam, and cherry aromas, red color, fruity by mouth, and acidic characters. Tannin concentration was significantly higher in the wines produced from low crop yields, consistent with the higher bitterness and astringency ratings given to those wines by descriptive analysis.We continued our investigation of the effects of crop yield on wine sensory quality using pruning and thinning trials on Cabernet Sauvignon grapes harvested in 2001.In the pruning trial, six treatments that left 12 to 48 buds/vine at pruning were imposed for the second consecutive season on the same vines. Vines were pruned to variations of 1 to 4 bud spurs and shoot thinned accordingly. These treatments resulted in 24 to 60 clusters/vine and produced yields that varied almost 2.5 times from lowest (3 tons/acre) to highest (8 tons/acre). In addition to yield components, a number of vegetative growth parameters were measured including budbreak, shoot diameter, and shoot length. There was only a slight decrease in shoot diameter, but shoot length was a strong inverse function of bud number, varying about 100%from highest to lowest bud number per vine. The cluster weight did not differ significantly among treatments. Although berry size was not constant among treatments, the differences were not greater than about 10%and did not show any clear relationship to the crop loads.In the thinning trial, vines were pruned to 2 or 4 bud spurs that were then cluster thinned at veraison to create 8 different crop load treatments. Crop load in this cluster thinning experiment was well distributed among the 8 thinning treatments, varying about 4-fold from 4 to over 16 lbs. per vine. These crop loads correspond to yields that vary from about 2 tons/acre to about 8 tons/acre. Thus, we were more successful in accomplishing low yield by cluster thinning than by severe pruning. There were 14 replicated yield treatments, six for the second year and eight for the first time in 2001. Wines were made from each treatment, and they are ready for bottling and subsequent sensory and chemical analysis this spring.

Effects of Berry Size and Crop Yield on Wine Composition and Sensory Quality

We draw these conclusions about the dependence of composition on size and irrigation:

  1. Imposing significant water deficits can decrease berry size and increase skin: juice ratio by approximately 25%compared to conventional irrigation regimes. From two separate yield experiments, it appears that smaller berries are not produced when yields are increased from 3.5 to over 10 tons/acre by leaving longer spurs at pruning.
  2. Berry size is highly correlated with seed mass/berry. However, berry growth did not keep pace with seed growth such that the amount of seed per unit berry mass increased with berry size. Low irrigation had less effect on seed growth than on mesocarp growth for any size of berry. Hence, Low irrigated fruit had greater relative seed mass, implying a greater concentration of seed tannin in the resultant wines.
  3. The mass of skin tissue bore a constant relation to berry size, i.e. the mass of skin per unit berry mass was relatively constant over the 3-fold range of berry sizes encountered. Low irrigated fruit had greater relative skin mass per berry. Low irrigation inhibited mesocarp growth more than skin growth such that the relative amount of skin per unit berry mass was always greater than for Control and High irrigated fruit.
  4. The amount of skin tannin per berry was a fairly constant fraction of berry size. Thus, the concentration of skin tannin in must was only slightly lower for large fruit than for small fruit (approximately 10%). However, the concentration of skin tannin was significantly greater in Low irrigation fruit of any size (approximately 30%greater in Low fruit).
  5. The amount of anthocyanin per berry increased with berry size, but was a slightly decreasing fraction of berry size. The resulting anthocyanin concentration was approximately 20%less from the largest fruit compared to small fruit. Again, the concentration was significantly greater (approximately 30%) in Low irrigated fruit for all fruit sizes.

These results show that the amount of each skin solute is not a constant that is diluted to varying degrees dependent upon fruit growth. Accumulation of skin solute is coordinated with growth. Accordingly, oft observed changes in fruit composition caused by water deficits are not attributable simply to differences in berry growth. There is an independent effect of deficit irrigation on composition. Because deficit irrigation produces lower yield, it is important to evaluate whether there is an independent effect of yield on these quality parameters.

The fruit size and irrigation differences in fruit composition were carried through to the resulting wines.

The differences in wine composition were slightly less dependent upon fruit size than the juice composition, suggesting a possible difference in “extractability”. And, both fruit and wine composition were much less sensitive to fruit size than the theoretical dependence that is predicted from differences in surface: volume of the berries. A preliminary investigation found differences among the low, control and high irrigation wines in the intensities of green beans aroma, red fruit by mouth, bitterness and astringency as shown below. When wines were made from different sized berries that were irrigated similarly, small berry wines were more astringent than large berry wines.

PDF: Effects of Berry Size and Crop Yield on Wine Composition and Sensory Quality

Determination and Consequences of Berry Size in Winegrape Production

A series of field experiments were conducted with Cabernet Sauvignon to investigate means of creating differences in berry size and the consequences thereof for winemaking. The primary focus was the hypothesis that irrigation alters wine composition primarily by changing berry size and the “dilution” of compounds of sensory significance. Additional questions included testing whether pruning to a high initial crop load and subsequent thinning could be used to manipulate berry size; attempting to make wine from berries of different size; and evaluating berry size distribution in clusters and on vines. Putting on a heavy crop load and thinning later was ineffective as a means of realizing smaller berries. Cluster thinning prior to veraison created four-fold differences in crop load, the highest being about 11 tons/acre. Yet the results clearly showed no differences in final berry size or color extracted from skins. This somewhat surprising result implies that even larger crop loads are required before berry growth becomes limited. It is in part for this reason that we propose to impose a wider range of crop loads and to investigate the consequences of crop load differences for wine chemical and sensory attributes in the coming season. When vines were differentially irrigated, mean berry volume was 17% greater with High irrigation (2x normal) compared to Low irrigation (minimal water applied). The predicted differences in must and wine composition would be of similar magnitude if there were no effects of vine water status on the amount of skin or seed solutes per berry. However, both anthocyanin and skin tannin per berry were greater in Low irrigated fruit than in the other treatments. Thus, irrigation regimes altered fruit composition by means other than simply berry expansion. Accordingly, the wine of Low irrigated fruit had 28%greater tannin concentration than the High irrigated wine (vs. the theoretical 17%). Seed tannin per berry (and seed mass) did not differ among irrigation treatments for any berry size class. In order to test the feasibility of sorting berry size for winemaking, hand harvested clusters were carefully destemmed, fruit sorted according to size, and made to wine. The tannin concentration was 13%greater in the small berry wine than in the other treatments; less than predicted on size alone. The results were promising in terms of the feasibility of developing technology to create small berry wines post harvest. However, it is not yet clear how important sorting might be to wine flavor, which is what we propose to address in the next funding cycle. Our informal bench tasting indicated treatment differences among irrigation and berry size treatments, the latter apparently differing in vegetative character. This report is limited to the data that have been analyzed to date with some limited interpretation of the implications of the data. However, the major tests were accomplished. We found that irrigation affected wine composition more than predicted by berry size alone and that sorting berry size had less than the hyothetical effect on wine tannin. Large differences in yield had no effect on berry size. We hope to pursue the sensory consequences of differences in yield, berry size, and irrigation.