Onset Of Veraison Research Articles

Effects of Apical, Late-Season Leaf Removal on Vine Performance and Wine Properties in Sangiovese Grapevines (Vitis vinifera L.)

An urgent challenge posed by climate change in warm grapevine-growing areas is accelerated ripening, which leads to rapid sugar accumulation while phenolics and aroma traits lag behind. Techniques that enable selectively delaying the sugar accumulation process without affecting the accumulation of secondary metabolites are essential. This study aimed to evaluate the effects of apical-to-cluster defoliation, manually applied in 2019 at the onset of veraison (D1) or 20 days later (D2), which removed about 30–40% of the pending total leaf area without altering the cluster microclimate compared with a non-defoliated control (C). Ripening trends, vegetative growth, yield components, and the final grape and wine composition, as well as wine sensorial attributes, were assessed. Although both treatments significantly lowered the final leaf area-to-yield ratio (0.80–0.90 m2/kg) compared with the 1.35 m2/kg recorded in the C vines, only D1 reduced the final total soluble solids (TSS) at harvest (2 °Brix less than C). However, the total anthocyanins were similarly limited, and titratable acidity (TA) did not differ from the C vines. The D1 wine was deemed similar to that made from control plants. Conversely, D2 failed to delay ripening, yet the D2 wine was deemed superior in terms of olfactory intensity, body, fruitiness, balance, and overall preference. Although the study was conducted over a single season, the results are robust enough to conclude that the timing of defoliation—i.e., the level of TSS concurrently reached by the C treatment—is crucial to achieving specific effects. Early defoliation appears valid for postponing ripening into a cooler period, making it quite interesting in warm–hot areas with a very long growing season; a much later defoliation, likely due to the interaction between mean canopy age and more light filtering from above the cluster zone, can elevate the quality of and appreciation for the final wine.

Effect of Applied Shading During Fruit Ripening on Tannin Structure-Activity Relationships of Grape Skin Extracts.

Historically, the effect of wine grape shading on flavonoids have investigated the impact of light incidence on proanthocyanidin (PA), flavonol, or anthocyanin concentration. In addition to concentration, the current experiment was designed to look at changes in proanthocyanidin composition, size and tannin activity through ripening. Tannin activity is a methodology for assessing the impact of structure and size on the affinity of tannin towards a hydrophobic surface and is considered to be a proxy for predicted astringency descriptive quality. In 2016 a shade cloth study was imposed on Cabernet Sauvignon on Mt. Veeder, within the larger Napa Valley viticultural area. A control, which was unshaded, and two treatments consisting of 40% and 80% shade were applied at the onset of veraison. Results showed significant differences in the composition and concentration of anthocyanins throughout ripening. Compositional differences in proanthocyanidin were also observed, where shaded treatments had a significantly higher proportion of galloylated subunits. The molecular mass of the extracted tannin was significantly lower in the unshaded control than in the 80% shade treatment. These factors led to a lower measured tannin activity in extracts from exposed fruit. This work suggests that manipulation of canopy architecture, such as artificial shading, leads to changes in berry pigmentation, tannin composition and activity. These results show that astringency and mouthfeel characteristics of a wine may be altered by vineyard management practices. This article is protected by copyright. All rights reserved.

Grape berry transpiration influences ripening and must composition in cv. Tempranillo (Vitis vinifera L.).

The implications of grape berry transpiration for the ripening process and final grape composition were studied. An experiment was conducted, under controlled conditions, with fruit‐bearing cuttings of Vitis vinifera L. cv. Tempranillo. Three doses of the antitranspirant di‐1‐p‐menthene were applied directly to the bunch at the onset of veraison: 1%, 5%, and 10% (v/v) (D1, D5, and D10, respectively). A treatment with bunches sprayed with water (D0) was also included as a control. Grape and bunch transpiration, and total soluble solids (TSS) accumulation rate decreased as the dose of antitranspirant increased, thus resulting in the lengthening of the ripening period. Bunch transpiration rates were linearly correlated with the elapsed time between veraison and maturity, and with the TSS accumulation rate. The evolution of pH, malic acid and total skin anthocyanins during ripening did not show remarkable changes as a consequence of the artificially reduced bunch transpiration. However, a decoupling between TSS and anthocyanins was observed. At maturity, the bunches treated with D10 had significantly lower must acidity and higher pH and extractable anthocyanin levels, these differences being likely associated with the lengthening of the ripening period. The results show a clear implication of grape transpiration for the ripening process and final grape composition, and give new hints on the direct application of antitranspirants to the bunch as a way to regulate sugar accumulation while avoiding the concurrent delay of color development.

Calcium and Potassium Accumulation during the Growing Season in Cabernet Sauvignon and Merlot Grape Varieties.

The evolution of calcium (Ca) and potassium (K) accumulation in grape berries during the growing season provided information on the productivity and quality of grape crops, considering that both elements have numerous physiological effects. The aim of the study was to determine and compare Ca and K accumulation in berries from ‘Cabernet Sauvignon’ and ‘Merlot’ grape varieties influenced by the number of days after flowering (DAF) over three consecutive growing seasons (2019–2021) in Recaş vineyards, from Banat Region in Western Romania. Results showed that Ca accumulation in the berries continued at slow rates after veraison when water was available for both varieties; accumulation was observed mainly in the skin, suggesting translocation from the flesh. Regression analysis showed a strong dependence on the interval of 65–75 DAF for Ca accumulation in the skin. K accumulation increased after the onset of veraison until 70 to 90 DAF in both varieties, with higher accumulation in the flesh than in the skin. No significant differences were found among varieties regarding the Ca and K content during the study period. In both varieties, the relationship between sugar accumulation and the Ca/K content was highly significant. Given the importance of both elements, new data may contribute to establishing the optimum grape ripeness in relation to the sugar concentration in the berries.

Forever Young? Late Shoot Pruning Affects Phenological Development, Physiology, Yield and Wine Quality of Vitis vinifera cv. Malbec

‘Malbec’ grapevines commonly have high yield, thus intermittently negatively affecting wine quality parameters. Here, we describe the use of late shoot pruning (LSP) practice applied for wine quality improvement. We examined the effect of timing of LSP on ‘Malbec’ vines grown in Mediterranean conditions during three consecutive seasons (2016–2018) in Israel. The timing of LSP treatment applications (applied one, two and three weeks after bud break) were compared with cluster-thinned, winter-pruned vines (WP + T) and standard winter pruning (WP). The LSP practice postponed bud break of target buds but did not have a temporal effect on the onset of veraison. Midday stem water potential was less negative and stomatal conductance and net CO2 assimilation rate were higher in the LSP vines. This practice led to a substantial reduction in the number of clusters and crop yield. Finally, wine quality was positively affected by applying LSP treatment. Performing the inexpensive LSP treatment at the precise timing after bud burst was found to save labor, decrease crop yield and improve grape and wine parameters. LSP application should be considered in adequate varieties as a significant tool for the enhanced effectiveness of vine growing in warm regions.

Changes of anthocyanins and residual ethylene of table grapes with color promotants treated

Different color-promoting treatments were tested on table grape cv. “Flame Seedlees” to evaluate changes on flavonoids such as anthocyanins and the residual ethylene produced. Treatments were spray-applied at the onset of veraison. The control was Ethrel at 250 ppm (ETH), Salicylic Acid at 100 ppm (AS), Melatonin at 25 ppm (MEL) and 1:1 mixtures of ETH+AS, ETH+MEL and AS+MEL. The trials were conducted in triplicate after harvest, measuring Total Soluble Solids (% TSS), total acidity (% tartaric acid), pH, residual ethylene (ppm) and anthocyanin content (mg∙cm-2). It was found that treatments ETH, AS, MEL and ETH+AS reached 16% TSS, standing out with lower values ETH +MEL (14.27%) and AS+MEL (15.17%) (p ≤ 0.05). ETH reached 0.83 ppm of residual ethylene, while a sum effect was appreciated in ETH+AS (0.5 ppm) and ETH+MEL (0.35 ppm), but not beneficial as it did not reflect quality characteristics. Only differences (p ≤ 0.05) in anthocyanin content were recorded between ETH (0.019 mg∙cm-2) and AS+MEL (0.003 mg∙cm-2). The subjective color of the grape bunches in the field made it possible to relate it to the objective results of the analyses performed. This research provides commercially important information on the substitution of Ethrel by natural compounds such as AS and MEL, as they show similar effects on the quality of “Flame Seedless” table grapes. In addition, these compounds do not have an ethylene residual greater than 0.2 mg/kg.

Transcriptomic analysis of temporal shifts in berry development between two grapevine cultivars of the Pinot family reveals potential genes controlling ripening time

BackgroundGrapevine cultivars of the Pinot family represent clonally propagated mutants with major phenotypic and physiological differences, such as different colour or shifted ripening time, as well as changes in important viticultural traits. Specifically, the cultivars ‘Pinot Noir’ (PN) and ‘Pinot Noir Precoce’ (PNP, early ripening) flower at the same time, but vary in the beginning of berry ripening (veraison) and, consequently, harvest time. In addition to genotype, seasonal climatic conditions (i.e. high temperatures) also affect ripening times. To reveal possible regulatory genes that affect the timing of veraison onset, we investigated differences in gene expression profiles between PN and PNP throughout berry development with a closely meshed time series and over two separate years.ResultsThe difference in the duration of berry formation between PN and PNP was quantified to be approximately two weeks under the growth conditions applied, using plant material with a proven PN and PNP clonal relationship. Clusters of co-expressed genes and differentially expressed genes (DEGs) were detected which reflect the shift in the timing of veraison onset. Functional annotation of these DEGs fit to observed phenotypic and physiological changes during berry development. In total, we observed 3,342 DEGs in 2014 and 2,745 DEGs in 2017 between PN and PNP, with 1,923 DEGs across both years. Among these, 388 DEGs were identified as veraison-specific and 12 were considered as berry ripening time regulatory candidates. The expression profiles revealed two candidate genes for ripening time control which we designated VviRTIC1 and VviRTIC2 (VIT_210s0071g01145 and VIT_200s0366g00020, respectively). These genes likely contribute the phenotypic differences observed between PN and PNP.ConclusionsMany of the 1,923 DEGs show highly similar expression profiles in both cultivars if the patterns are aligned according to developmental stage. In our work, putative genes differentially expressed between PNP and PN which could control ripening time as well as veraison-specific genes were identified. We point out connections of these genes to molecular events during berry development and discuss potential candidate genes which may control ripening time. Two of these candidates were observed to be differentially expressed in the early berry development phase. Several down-regulated genes during berry ripening are annotated as auxin response factors / ARFs. Conceivably, general changes in auxin signaling may cause the earlier ripening phenotype of PNP.

Influence of attenuated reflected solar radiation from the vineyard floor on volatile compounds in Cabernet Sauvignon grapes and wines of the north foot of Mt. Tianshan

In this study, fruit-zone microclimate was modified by three treatments, including inter-row mulch (M), the combination of leaf removal applied at the onset of veraison and inter-row mulch (MLR-BV), and the combination of leaf removal applied at complete veraison and inter-row mulch (MLR-EV), in a semi-arid climate in three consecutive years (2015–2017). M decreased fruit-zone reflected solar radiation from vineyard floor and low temperature (10–20 °C) duration, whereas it increased soil temperature and high temperature (> 30 °C) duration. MLR-BV and MLR-EV increased fruit-zone incident photosynthetically active radiation while decreased the duration of 20–25 °C compared to M. Notably, M significantly decreased grape total norisoprenoid concentrations in 2015–2017, and total terpenoid concentrations in 2015–2016. Applying leaf removal applied at the onset of veraison could compensate the decreases of total norisoprenoids and terpenoids caused by M when two treatments were applied together. Besides, M significantly increased grape total C6/C9 compound concentrations, besides, (Z)-3-hexen-1-ol concentrations were significantly higher in grapes of M than those of MLR-BV in 2015–2017. Light exposure and high temperature duration after veraison had strong positive correlations with total norisoprenoids and terpenoids, besides, low temperature duration was positively correlated with total norisoprenoids. In addition, light exposure after veraison had strong negative correlations with total C6/C9 compounds. With respect to the volatile compounds in wines, M significantly decreased the concentrations of isopentanol and ethyl acetate, and the concentrations of ethyl cinnamate, phenylacetaldehyde, phenylethyl alcohol and 3-methylthio-1-propanol were significantly lower in MLR-BV and MLR-EV than in M. The outcome of this study can assist winegrowers to properly adjust vineyard managements to optimize the concentrations of desired volatile compounds in grapes and wines.

Foliar Application of an Amino Acid-Enriched Urea Fertilizer on 'Greco' Grapevines at Full Veraison Increases Berry Yeast-Assimilable Nitrogen Content.

Reaching a sufficient yeast assimilable nitrogen (YAN) content in berries at harvest is considered a main viticultural goal for wine-making, because low YANs can slow down must fermentation and have negative effects on wine sensory attributes. For this reason, many attempts have been made to define correct fertilization strategies to stimulate YAN accumulation in the berries. Foliar application of amino acid-enriched urea fertilizer is considered a promising environmentally friendly strategy for improving the yield and nutrient efficiency of plants. The aim of this two-year research was to study the effects of two fertilizers based on urea enriched with amino acids applied at low doses in diverse phenological stages on berry YAN concentration in ‘Greco’ grapevines. The results of this study indicate that amino acid-enriched urea fertilizers induced an increase in YANs in the ‘Greco’ berries at harvest, but only when the application was undertaken at full veraison. Foliar applications applied at veraison onset or post-veraison appeared to be ineffective. In addition, the fertilizers enhanced YAN accumulation in the berry without modifying the other composition parameters measured in this study (total soluble solids, titratable acidity, pH and malic acid). Therefore, the results of our study suggest that foliar application of urea fertilizers enriched with amino acids is an effective strategy to increase yeast-assimilable nitrogen concentration in grapevine berries at harvest.

Vegetative, Yield, and Berry Quality Response of Aglianico to Shoot-Trimming Applied at Three Stages of Berry Ripening

The rise in air temperature due to climate change is causing an increase in the sugar accumulation rate in grape berries, resulting in increased wine alcohol concentrations. Postveraison leaf area removal (defoliation, shoot-trimming) is a suitable canopy management strategy to slow carbohydrate accumulation in the berries. However, in late-ripening cultivars, the phenological stage between veraison onset and harvest can be very long. Therefore, it can be hypothesized that the specific timing when leaf area removal is applied during the phenological stage can affect carbohydrate accumulation in the berries and berry composition. A two-year experiment was designed to compare the responses of Aglianico grapevines, a late-maturing cultivar, to shoot-trimming applied at three different stages of berry ripening. The experimental design included: (a) three trimming treatments applied at total soluble solids of 6, 12, and 18 Brix, respectively; and (b) a control treatment (untrimmed vines). Independent of the application timing, shoot-trimming decreased berry total soluble solids at harvest below that of control vines, but the later the shoot-trimming was applied, the lower berry total soluble solids was at harvest. Shoot-trimming did not affect other berry parameters. These results confirm that, at least for late-maturing cultivars, the timing of application of late shoot-trimming plays a key role in modulating the intensity of the effects of this management practice on berry composition.

Changes in global aroma profiles of Cabernet Sauvignon in response to cluster thinning.

Cluster thinning (CT) is a common practice to prevent overcropping in viticulture. CT affects vine balance between vegetative and productive growth and further modifies grape composition. This study investigated the effects of cluster thinning treatments applied at pea-size stage (CT-AF) and the onset of veraison (CT-V), respectively, on volatile compounds of Cabernet Sauvignon in two seasons (2013-2014). The experimental vineyard was located in the north-west of China with semi-arid and monsoon climate. CT exhibited limited effects on the evolutions of volatile compounds. CT-AF exhibited an inhibition on 6-methyl-5-heptene-2-one accumulation. There were no differences in terpene concentrations between CT-treated and control grapes regardless of CT time. Regarding C6/C9 compounds and their derivatives, CT-AF decreased nonanal concentration whilst CT-V increased (Z)-3-hexen-1-ol concentration. Additionally, there were increases in nonanal, (E)-2-hexen-1-ol, (Z)-2-hexen-1-ol and (Z)-3-hexen-1-ol concentrations in grapes with delayed CT. Among benzene derivatives, earlier CT resulted in lower phenol concentrations.

Melatonin promotes ripening of grape berry via increasing the levels of ABA, H2O2, and particularly ethylene

The role of melatonin in the regulation of fruit ripening and the mechanism involved remain largely unknown. In “Moldova” grape berries, melatonin accumulated rapidly from onset of veraison, reached the maximum at 94 days after bloom (DAB) and then exhibited low levels at late stages of berry ripening. By contrast, abscisic acid (ABA) and hydrogen peroxide (H2O2) exhibited different accumulation patterns, and ethylene was primarily produced immediately before veraison. Further experiments demonstrated that 10 and particularly 100 µM melatonin treatments increased the levels of ABA, H2O2, and ethylene production and promoted berry ripening compared with the control treatment, whereas 0.1 and 1.0 µM melatonin did not lead to clear effects. Additionally, the application of inhibitors indicated that ABA, H2O2, and ethylene participated in the regulation of berry ripening induced by melatonin, and the suppression of ethylene biosynthesis produced the greatest inhibitory effects on melatonin-induced berry ripening compared with those of ABA and H2O2. Melatonin also promoted ethylene production via ABA. In summary, 10 and particularly 100 µM melatonin treatments promoted berry ripening, which was accomplished, at least partially, via the other signaling molecules of ABA, H2O2, and particularly ethylene. This research provides insight into melatonin signaling during berry ripening and may advance the application of melatonin to accelerate berry ripening.

Exogenous Applications of Brassinosteroids Improve Color of Red Table Grape (Vitis vinifera L. Cv. "Redglobe") Berries.

Color and other quality parameters of “Redglobe” grape (Vitis vinifera L.) berries were evaluated after treatment with brassinosteroid (BR) analogs. Three BRs analogs (24-epibrassinolide, Triol, or Lactone) were applied at three concentrations (0.0, 0.4, or 0.8 mg⋅L-1), at the onset of veraison. A commercial formulation (B-2000®) was also applied, at a recommended rate of 0.06 mg⋅L-1. The tested BR analogs were effective improving berry color (evaluated as color index for red grapes, CIRG), increasing the levels of soluble solids and anthocyanins, and changing the types of anthocyanins present without altering other quality and yield parameters. The effects of BR analogs on color enhancement could be explained by an increase in soluble solids content and/or anthocyanin content. Treatment with 24-epibrassinolide (at 0.4 mg⋅L-1) or the commercial formulation tended to favor the production of dihydroxylated anthocyanins, which are responsible for the red and pink colors of grape berries. Results indicate that the use of BRs constitutes a potential tool in the production of table grapes. This is the first report of this enhancement effect in a productive context.

Exogenous 24-Epibrassinolide Interacts with Light to Regulate Anthocyanin and Proanthocyanidin Biosynthesis in Cabernet Sauvignon (Vitis vinifera L.).

Anthocyanins and proanthocyanidins (PAs) are crucial factors that affect the quality of grapes and the making of wine, which were stimulated by various stimuli and environment factors (sugar, hormones, light, and temperature). The aim of the study was to investigate the influence of exogenous 24-Epibrassinolide (EBR) and light on the mechanism of anthocyanins and PAs accumulation in grape berries. Grape clusters were sprayed with EBR (0.4 mg/L) under light and darkness conditions (EBR + L, EBR + D), or sprayed with deionized water under light and darkness conditions as controls (L, D), at the onset of veraison. A large amount of anthocyanins accumulated in the grape skins and was measured under EBR + L and L treatments, whereas EBR + D and D treatments severely suppressed anthocyanin accumulation. This indicated that EBR treatment could produce overlay effects under light, in comparison to that in dark. Real-time quantitative PCR analysis indicated that EBR application up-regulated the expression of genes (VvCHI1, VvCHS2, VvCHS3, VvDFR, VvLDOX, VvMYBA1) under light conditions. Under darkness conditions, only early biosynthetic genes of anthocyanin biosynthesis responded to EBR. Furthermore, we also analyzed the expression levels of the BR-regulated transcription factor VvBZR1 (Brassinazole-resistant 1) and light-regulated transcription factor VvHY5 (Elongated hypocotyl 5). Our results suggested that EBR and light had synergistic effects on the expression of genes in the anthocyanin biosynthesis pathway.

Implications of the Presence of Maturing Fruit on Carbohydrate and Nitrogen Distribution in Grapevines under Postveraison Water Constraints

Grapevine (Vitis vinifera) berries are sugar and nitrogen (N) sinks between veraison and fruit maturity. Limited photoassimilation, often caused by water constraints, induces reserve total nonstructural carbohydrate (TNC) remobilization, contributing to berry sugar accumulation, while fruit N accumulation can be affected by vine water supply. Although postveraison root carbohydrate remobilization toward the fruit has been identified through 14C tracing studies, it is still unclear when this remobilization occurs during the two phases of berry sugar accumulation (rapid and slow). Similarly, although postveraison N reserve mobilization toward the fruit has been reported, the impact of water constraints during berry N accumulation on its translocation from the different grapevine organs requires clarification. Potted grapevines were grown with or without fruit from the onset of veraison. Vines were irrigated to sustain water constraints, and fortnightly root, trunk, shoot, and leaf structural biomass, starch, soluble sugar, total N, and amino N concentrations were determined. The fruit sugar and N accumulation was also assessed. Root starch depletion coincided with root sucrose and hexose accumulation during peak berry sugar accumulation. Defruiting at veraison resulted in continuous root growth, earlier starch storage, and root hexose accumulation. Leaf N depletion coincided with fruit N accumulation, while the roots of defruited vines accumulated N reserves. Root growth, starch, and N reserve accumulation were affected by maturing fruit during water constraints. Root starch is an alternative source to support fruit sugar accumulation, resulting in reserve starch depletion during rapid fruit sugar accumulation, while root starch refills during slow berry sugar accumulation. On the other hand, leaf N is a source toward postveraison fruit N accumulation, and the fruit N accumulation prevents root N storage.

Early Leaf Removal has a Larger Effect than Cluster Thinning on Grape Phenolic Composition in cv. Teran

This study aimed to assess the effects of early leaf removal (ELR) and cluster thinning (CT) on vegetative growth, yield components, and berry composition of Teran (Vitis vinifera L.) grown in the Istria region of Croatia. Both treatments were compared with an untreated control (UC) during the 2012 and 2013 growing seasons. ELR involved the removal of six basal leaves at the preflowering stage, while in CT, 35% of clusters were removed at the onset of veraison. Both ELR and CT resulted in lower yield per vine compared to UC (22 and 37% less, respectively), and in greater Brix at harvest (+1.3 and +1.0, respectively). The concentration of total phenolics in grapes increased by 19% in ELR and by 6% in CT compared to UC, while total anthocyanin concentrations increased only in ELR (+20% versus UC). Despite greater yield and a lower leaf area-to-yield ratio compared to CT, ELR achieved higher total anthocyanin and phenolic concentration, suggesting that ELR is more suitable than CT for the production of high-quality Teran grapes.

Effects of Irrigation and Cluster Thinning on Tempranillo Grape and Wine Composition

With the aim of understanding the effects of water stress and cluster load on berry composition and wine quality, a four-year field test was conducted in a cv. Tempranillo vineyard in Extremadura (Spain). When the first berries appeared to be changing colour (onset of veraison), grapevines were subjected to two different irrigation regimes, one supplying 100% of crop evapotranspiration, and the other 25%. In addition, two cluster load levels were tested for each irrigation regime: seven to nine and four to five clusters/m2 planting area. Both irrigation and thinning had an impact on most of the parameters analysed in the grapes and the wines, although the thinning effect was in general higher than the irrigation effect. Thus, deficit irrigation reduced malic acid and the titratable acidity of Tempranillo grape juice, while cluster thinning increased all parameters analysed, except potassium concentrations. Similarly, the wine composition was also affected differently by irrigation and by cluster thinning. Deficit irrigation reduced pH and increased titratable acidity, total phenol index and colour parameters, while cluster thinning increased alcohol content, anthocyanin and colour intensity, and reduced pH and colour. The effect of the cluster thinning technique was independent of the irrigation regime in most of the wine parameters analysed, except for total phenol index, where the effect of deficit irrigation (DI) was more pronounced in grapevines also subjected to the cluster thinning treatment.

Phenologic and growth responses to early and late season water deficits in Cabernet franc

Phenologic and ontogenic responses to seasonal water deficits were investigated in the wine grape variety, Cabernet franc, in a California hillside vineyard. Water deficits were imposed by withholding irrigation water before or after the onset of veraison. In continually irrigated vines, midday leaf water potential (Ψ) declined from - 0.4 MPa to approximately -1.1 MPa between budbreak and veraison despite weekly irrigation at a rate which was 2 x the normal production practice for that commercial vineyard. Hence, water deficits may be a common component of grape production in hillside vineyards of California. When water was withheld until veraison, midday Ψ declined more rapidly and reached - 1.4 MPa at the time water was resupplied. For these vines, water status slowly recovered to the level of the continually irrigated vines. The water status of late deficit vines, (water withheld after veraison), decreased rapidly after veraison, reaching a minimum of - 1.6 MPa at harvest. These differences in vine water status had no effect on the major phenological indicators, i. e„ the timing (on basis of time or accumulation of degree days) of bloom, veraison, and harvest. However, early season deficits shortened the period of shoot elongation and node production, decreased the maximum rate of shoot elongation and node production, and accelerated periderm development on current season shoots. Possible ecological implications of accelerated periderm development are discussed. Shoot length and the number of nodes/shoot was reduced approximately 25 % by the early season water deficits. Radial shoot growth was also inhibited by early deficits but much less than axial shoot growth. Shoot growth had essentially ceased in all vines before late season deficits developed. The characteristic double-sigmoid growth pattern of berries was observed regardless of seasonal water deficits. Most fruit growth occurred during the first growth phase in all treatments. The rate of fruit growth was inhibited by early and late season water deficits. Yield was decreased more by early deficits than by late deficits.

Impact of light exposure on fruit composition of white 'Riesling' grape berries (Vitis vinifera L.)

Microclimate and irradiation have long been known to influence winegrape (Vitis vinifera) quality. However, microclimate influence on white grape quality has remained understudied, as most research efforts have focused on red varieties and their anthocyanin content. In this study, we investigated microclimatic effects on the phenolic and amino acid composition of white 'Riesling' grapes using bunch shading and leaf removal to manipulate grape microclimate. Both treatments were applied directly after fruit set (modified E‑L 27; (Coombe 1995)) as well as at the onset of veraison (E-L 34), and compared to a non-manipulated control. The concentration of malic acid, amino acids and total nitrogen were decreased by illumination during the berry growth, while content and concentration of phenolics were significantly increased by illumination. Strong negative correlations were observed between accumulation of amino acids and flavonols. Although accumulation of flavonols occurred throughout berry development, the most important phase of accumulation was post-veraison.

Berry development of grapevines: Relations between the growth of berries and their DNA content indicate cell multiplication and enlargement

DNA of berries (cv. Shiraz) was extracted and quantified to determine, indirectly, the rate of cell division and enlargement in the grape pericarp. The increase of total DNA in the pericarp begins at anthesis in the ovary of grapevine flowers (day 0, 100 % of flowers at full bloom). This increase in DNA continues during the herbaceous growth period until 35 d after anthesis (day 35, 19 d before the onset of veraison). Total DNA per berry pericarp does not increase linearly during this growth period since 75 % of the DNA has already accumulated before day 20. We determined a cell enlargement index (CEI), to estimate the mean cellular volume. The pericarp cell size increases 16-fold during the whole growth of berries. Volume increase is nearly linear from berry set to the beginning of veraison and thereafter until maturity. The importance of determination of cell division and enlargement of berry pericarp based on the DNA content and its possible application in studies on the influence of environmental factors on berry growth is discussed.