Accumulation of potassium and calcium by ripening berries on field vines of Vitis vinifera (L) cv. Shiraz

Ripening berries of Vitis vinifera (L) cv. Shiraz can show pre-harvest weight loss at sub-optimal sugar content (shrinkage). This later-age decline in berry weight implies that water loss from mature berries has begun to exceed water inflow from the parent grapevine. Such decrease in net inflow has been attributed to a cessation of xylem flow subsequent to veraison, followed by a cessation of phloem flow into berries during later stages of ripening. We address this issue in this present paper, and show a continuing increase in berry content of both potassium and calcium throughout ripening. We measured changes in berry fresh weight and berry content of potassium (phloem mobile) and calcium (phloem immobile) in fruit on field vines sampled from set to harvest. Berry fresh weight reached a plateau between 81 and 95 days after flowering, then declined to 75% of maximum fresh weight by 115 days. Dry weight maximum occurred 14 days after the onset of the fresh weight plateau. Potassium accumulation was slow pre-veraison, increased 3.5-fold post-veraison, and continued during berry shrinkage. Calcium content per berry also showed a linear increase throughout fruit enlargement and ripening phases. Assuming both potassium and calcium were entering berries via vascular conduits, our results imply a continuing connection between parent grapevine and ripening berries. Moreover, an abrupt change (increase) in the ratio of potassium/calcium content per berry subsequent to veraison implies that phloem inflow has increased relative to xylem inflow during post-veraison enlargement.     

Dynamics of grape berry growth and physiology of ripening

Data from two experiments on development of grape berries is re-examined with emphasis on partitioning of berry weight into non-solutes per berry (largely water) and solutes per berry (largely sugar), using weight times juice °Brix. This approach is based on the thought that, since xylem flow is blocked after veraison, time curves of solutes per berry indicate the activity of phloem transport into the berry during ripening growth. Experiment 1: Measurements of Muscat Gordo Blanco berries from inflorescences with a spread of flowering times showed typical double-sigmoid volume/time curves but with divergent rates and amounts of volume increase. Despite this divergence, °Brix curves after veraison were almost coincident because, in each case, the rate of increase in solutes per berry was proportional to that of berry volume. These results indicate that sugar and water increments after veraison are linked and depend on the same source, namely, phloem sap. Experiment 2: An irrigation experiment on cv. Shiraz also showed divergent berry weight curves between treatments and years but with the difference that all berries shrank after a maximum berry weight was attained at 91 days after flowering (at about 20 °Brix). At this point, the curves of solutes per berry slowed then plateaued, indicating that inflow of phloem sap had become impeded. Prior to shrinkage these berries accumulated primary metabolites (mainly phloem sugar) but, during shrinkage, when berries were apparently isolated from vascular transport, non-anthocyanin glycosides accumulated. These results have implications for the study of berry flavour buildup and berry composition, and also for the understanding of sink competition within the vine, fresh and dried yield, and juice °Brix levels.     

Vascular function in berries of Vitis vinifera (L) cv. Shiraz

Anatomical studies on the movement of a xylem tracer dye were combined with functional studies on changes in grape berry volume during final stages of berry ripening to gauge xylem effectiveness. Movement of a xylem tracer dye into pre-veraison fruit was compared with movement into post-veraison fruit by feeding a solution of acid fuchsin to excised shoots with bunches still attached, and then sectioning fruit for photo-microscopy. Those comparisons confirmed published studies showing an apparent blockage to dye movement along major vessels within the brush tissue of post-veraison fruit. However, our functional approach yielded a different impression of vascular activity. A continuation of xylem transport in ripening fruit was inferred from comparisons of berry volume where pedicels were either girdled (phloem interrupted, but xylem intact) or excised (both phloem and xylem interrupted). Volume changes in manipulated berries were compared with immediately adjacent intact control berries within the same bunch. Control fruit lost volume subsequent to 78 days after flowering (DAF) while manipulated fruit lost volume from the first day of treatment at 67 DAF. By harvest time at 95 DAF, both control fruit and girdled fruit had fallen to 91% and excised fruit to 46% of maximum volumes recorded around 78 DAF. Berry volume loss in girdled fruit was further enhanced by deficit irrigation. We conclude that xylem flow into those Shiraz berries must have continued beyond veraison despite dye evidence of a vessel blockage within the brush region of analogous post-veraison fruit.     

Is weight loss in ripening grape berries cv. Shiraz caused by impeded phloem transport?

Berry shrinkage in ripening grapes cv. Shiraz is systemic within a given grapevine and coincident between grapevines in any given season. In this present study on weight loss in ripening berries, ripening curves of non-solutes per berry (largely water) were similar to curves for berry weight (as a function of time). Both sets of curves were equivalent with respect to timing of maximum weights and subsequent rates of weight loss. However, curves of solutes per berry (largely sugar) increased steeply up to the time of maximum berry weight, then slowed and plateau-ed. We suggest that phloem sap is the sole source for water and solutes that enter grape berries subsequent to veraison, and accumulate until maximum berry weight. We further suggest that phloem flow becomes impeded at maximum berry weight.
As berry ripening proceeds, continuation of berry transpiration leads to berry shrinkage and a concentration of solutes; i.e. any increase in juice Brix depends on shrinkage. One implication is that assimilates enter a berry up to the onset of shrinkage, whereafter accumulation of non-anthocyanin glycosides (including glycosides of flavour compounds) depends upon their synthesis in situ.     

Synthesis of flavonols and expression of flavonol synthase genes in the developing grape berries of Shiraz and Chardonnay (Vitis vinifera L.)

Flavonols were determined in Shiraz and Chardonnay grapes throughout berry development. The predominant flavonols were quercetin-3-glycosides with trace amounts of kaempferol-3-glycosides detected in Shiraz flowers but not in developing berries. Flavonols were present in the skin of ripening grapes but were not detected in seeds or flesh. Flavonols were also present in buds, tendrils, inflorescences, anthers and leaves. The concentration of flavonols in flowers (mg/g fresh weight) was high and decreased between flowering and berry set then remained relatively constant through berry development. The total amount of flavonols in berries (mg/berry) was low until pre-veraison then increased during berry development, particularly before veraison, the onset of ripening, in Chardonnay and during ripening in Shiraz. Two cDNA fragments with homology to genes encoding the enzyme flavonol synthase (FLS) were isolated from Shiraz flowers. In the overlapping region of the two cDNAs, they had 80% sequence identity at the nucleotide level and both had high homology to FLS genes from other plants. VvFLS1 was expressed in leaves, tendrils, pedicels, buds and inflorescences as well as in developing grapes. Expression was highest between flowering and fruit set then declined, increasing again during ripening coincident with the increase in flavonols per berry. Expression of VvFLS2 was much lower than for VvFLS1 and did not change during berry development. The results indicate that two distinct periods of flavonol synthesis occur in grapes, the first around flowering and the second during ripening of the developing berries.     

Survival and growth of Aspergillus carbonarius on wine grapes before harvest

Aspergillus carbonarius, the primary OTA-producing species in Australia, was inoculated onto the surface of Chardonnay and Shiraz bunches at pre-bunch closure, veraison and pre-harvest during the 2002-03 and 2003-04 seasons. Mean A. carbonarius counts decreased between pre-bunch closure and veraison, and increased between veraison and pre-harvest. Increases in A. carbonarius counts from veraison onwards were most marked in Chardonnay bunches during 2003-04; such bunches comprised more berries and were heavier than in 2002-03. Bunches with no berry damage yielded low A. carbonarius counts at pre-harvest and harvest. Exposure to direct sunlight over several days reduced viability of A. carbonarius spores supported on filter membranes by 10(5), despite the spores having thick, heavily melanised walls. The estimated cumulative UV exposure for that period was 10 mWh. Thus, UV radiation may be a contributory factor to the decline of A. carbonarius spores on berry surfaces, particularly in the early stages of berry development.     

Influence of shriveling on berry composition and antioxidant activity of Cabernet Sauvignon grapes from Shanxi vineyards

BACKGROUND: Berry shrivel (BS), a berry development disorder, appears soon after veraison. It occurs worldwide and affects the quality of grape berries and wine. However, it had not been reported in China until recently. This study aimed to investigate the changes in berry composition and antioxidant activity of Cabernet Sauvignon grapes from Xiangning Valley, Shanxi Province, China, during BS. RESULTS: Shrinkage contributed to an increase in the concentration of basic grape ingredients such as sugar and acid. An appropriate degree of shrinkage was apparently helpful in improving the phenolic content and increasing the antioxidant activity, but the berries that continued to shrivel showed a low antioxidant activity. Further, the results indicated distinct differences between the berries harvested from the southern side of the canopy and those harvested from the northern side, presumably due to variations in sunlight exposure. CONCLUSION: Moderate BS was beneficial since it increased berry quality and antioxidant activity of Cabernet Sauvignon grapes from Shanxi vineyards. Copyright © 2011 Society of Chemical Industry     

Rootstock and salinity effects on rates of berry maturation, ion accumulation and colour development in Shiraz grapes

Shiraz grapevines on either their own roots, or on the rootstocks Ramsey, 1103 Paulsen, 140 Ruggeri or 101–14, were grown at two separate sites within the Murray‐Darling viticultural region with similar irrigation regimes but with an irrigation water salinity of either 0.43 dS/m (low salinity site) or 2.3 dS/m (high salinity site). Rootstock effects on grape berry development, ion concentrations, soluble solids and acidity were followed during one season. Wines were also made and compared using spectral analysis and sensory evaluation. Rootstock effects that were common across both sites were (1) a close relationship between K+and soluble solids accumulation in developing grape berries which commenced at the onset of veraison and was indicative of a link between K+and sucrose transport in the phloem, and (2), higher wine K+, pH and colour hue for all rootstocks with one exception, namely 101–14 at high salinity where 101–14 responded similarly to own roots. Juice K+, pH and loss of K+from juice during winemaking were highest for grapes from the high salinity site. Mean berry weight was smaller and the range in berry size across rootstocks was narrower at the saline site. The narrower range in berry sizes may have contributed to fewer rootstock effects on wine spectral characteristics at high salinity. There was no effect of rootstock on CO₂ assimilation rate or stomatal conductance at either site, although intrinsic leaf‐based water‐use efficiency measured as A/g was 50% higher at the saline site. All treatments exhibited berry shrivel at maturity, but the extent was smaller at high salinity. Slower development of berry colour during veraison was observed on some rootstocks, for example 101–14, and while unrelated to canopy size per se, a higher leaf‐to‐fruit ratio for 101–14 may have been a factor. Slower berry colour development during veraison had no bearing on the colour density of wine made from the harvested grapes.     

Variation in Shiraz berry size originates before fruitset but harvest is a point of resynchronisation for berry development after flowering

Background and Aims:  Asynchronous berry development results in variation in berry size and berry composition. Variation in berry size affects vineyard yield, wine quantity and berry composition, while variation in berry composition affects fruit flavour and wine quality. The objective of this study is to identify when variation in berry size begins.
Methods and Results:  Shiraz bunches were sampled at seven stages throughout the growing season and the development of individual berries was characterised by measurements of weight, volume, surface area, deformability, seed number and seed weight. Coefficients of variation with respect to berry weight, volume and surface area were elevated throughout the post-flowering period but declined as the berries approached harvest ripeness.
Conclusions:  Variation in berry size originates prior to berry set, most probably during differentiation in the floral primordium at budburst. Harvest represents a point of resynchronisation in berry development when a number of physiological changes become synchronised between berries and within the bunch.
Significance of the Study:  Variation in berry size is presumed by the wine industry to have a negative impact on crop level, fruit composition and wine quality. Much of this presumption is scientifically unsubstantiated. The findings of this paper should encourage grapegrowers and winemakers to modify the timing of the harvest to coincide with a reduction in variation in berry size.     

Relative proportions of seed, skin and flesh, in ripe berries from Cabernet Sauvignon grapevines grown in a vineyard either well irrigated or under water deficit

Relationships between the fresh mass of seed, skin (exocarp), and flesh (mesocarp) in six different berry size categories, were assessed on ripe fruit from Cabernet Sauvignon grapevines exposed to either High (H), Control (C) or Low (L) water status during post‐veraison berry growth in a vineyard. Berries harvested from each treatment were segregated into six mass categories in order to distinguish between changes in fresh mass components associated with general variation in berry size (on well‐watered grapevines), and those associated with berry size differences due to water stress. Berry fresh mass across all treatments ranged from about 0.4 to 2.0 g. Fresh mass components for both H and C berries comprised approximately 5% seed, 15% skin, and 80% flesh, regardless of variation in berry size, although there was some increase in seed mass relative to whole‐berry fresh mass in larger berries. Berry growth (as inferred from fresh mass at harvest) was much less sensitive to water deficit than published reports for grapevine shoot growth. Midday leaf water potentials around –1.20 MPa (Control) were not sufficient to inhibit berry growth. However, midday water potentials around –1.50 MPa (Low water status) inhibited berry growth by 13–18% of that attained by grapevines grown at high water status (i.e. treatment H where midday leaf water potentials remained around –1.00 MPa). Inhibition of berry growth by water deficit was attributed almost exclusively to reduced growth of mesocarp tissues (for most berry size categories). Water deficit thus increased the proportion of whole‐berry fresh mass represented by seeds and skin (for most berry size categories). Changes in those proportions due to irrigation treatments exceeded differences associated with general (non‐stress) variation in whole‐berry fresh mass. Excluding adverse environmental impacts on whole‐berry fresh mass, our results point to a limited role for variation in berry size per se as a factor determining the solute concentration of juice or wine derived from different sized fruit. By implication, and for all categories of whole‐berry fresh mass represented here, late season water deficit can result in ripe fruit with more skin and seed tissues (relative to whole‐berry fresh mass) compared with well‐watered control fruit.     

Shiraz berry size in relation to seed number and implications for juice and wine composition

This study was conducted over three seasons on irrigated Shiraz grapevines growing in a warm climate. We addressed the question of whether differences in berry size (within a population of berries from minimally pruned, own‐rooted or Ramsey‐grafted vines), would lead to differences in juice composition, wine composition or wine sensory score. Predictably, berry mass was found to increase with seed number, but berries in the smallest mass categories (0.3–0.7 g) still had similar juice soluble solids and pH; and similar concentrations of K+, tartaric acid and malic acid, compared with larger berries (1.4–2.0 g). Only for the very smallest mass category (0.3–0.55 g) was there any indication of better colour density (both for own‐rooted and Ramsey‐grafted vines) or higher anthocyanin concentration (for own‐rooted vines) compared with larger berries (1.4–2.0 g). Concentrations of tartaric acid and K+ in berry skins were highest in the smallest berry mass categories (0.3–0.7 g) and decreased with increasing berry mass (up to 1.4–2.0 g). A strong correlation (R²= 0.85) between skin tartaric acid and K+ concentrations was observed across that range. Small‐scale wine lots based on small berries (0.8–0.9 g) versus large berries (1.2–1.3 g) showed no differences in measures such as soluble solids, total acids or pH of juice; nor any differences in pH, total acids, K+, tartrate, malate, spectral characteristics or sensory score of corresponding wines. Moreover, small berries had a similar skin to fruit ratio, and a similar juice yield, compared to large berries. However, when measured post‐fermentation, the ratio of seed weight to skin weight was higher for small berries. The mass range of berries used here for small‐scale winemaking (i.e. from 0.8–0.9 g up to 1.2–1.3 g), covered the range of Shiraz berry mass typically found in irrigated vineyards (from 0.8 to 1.5 g), and thus confirms the relevance of present outcomes to practical winemaking. Finally, our data for variation in juice and wine composition as a function of berry size, showed consistent trends for all seasons, and thus implies that reported instances of improved wine quality from small berries (often associated with certain pruning treatments or deficit irrigation strategies), are more likely due to treatment effects that lead to small fruit, rather than to intrinsic developmental differences between large and small berries.     

Effect of short-term temperature and shading on fruit-set, seed and berry development in model vines of V. vinifera, cvs Chardonnay and Shiraz

Small Chardonnay and Shiraz vines were grown under controlled environment conditions at 25/20°C and 400 μE/(m².s) radiant energy. These conditions were interrupted for some plants for one week, at two periods near flowering, by imposing reduced temperatures (17°/14°C or 12°/9°C) and shading (8, 40 or 72% light reduction), in factorial combinations. Fruit-set was reduced by exposure to the lower temperature regime in both cultivars (confirming the results of a previous experiment) and tended also to decrease with increasing intensity of shading. Seed characteristics were examined only in Chardonnay where total number of seeds per berry was not affected by any of the treatments. However, pre-flowering exposure to 12°/9°C resulted in fewer berries with one or two sinker seeds and more berries with floater seeds and, overall, in a greater proportions of seeds being floaters. Shading had little effect on seed development. Berries on vines exposed to 12°/9°C, at both stages of development, had lower pericarp and seed weights compared with those treated with 17°/14°C or 25°/20°C. At harvest, pericarp weight and seed weight per berry were positively correlated; the linear regression for berries exposed to the higher temperature regimes had a significantly steeper slope than that for berries exposed to the lowest temperature regime. It is concluded that differences in pericarp weight were due to differing cell numbers. These differences may have developed firstly in the ovary due to a direct effect of exposure to varying temperature regimes, and secondly in the developing berry after fruit-set because of variation in the stimulatory activity of the seeds, caused by residual effects of pre-flowering temperature conditions on ovule and seed development.     

Weight loss from ripening berries of Shiraz grapevines (Vitis vinifera L. cv. Shiraz)

Environmental and phenological correlatives associated with the onset of weight loss during ripening in Vitis vinifera cv. Shiraz berries were examined. An irrigation experiment concerned with transient water deficit effects on berry growth over four consecutive seasons provided source data. Timing of maximum berry weight was more closely correlated with the number of days after flowering than with temperature summation. Prior to maximum berry weight, Brix was more closely correlated with days after flowering than with temperature summation, while the number of days from flowering to 10 and 15Brix was remarkably uniform despite contrasting seasons. Driving variables for weight loss during advanced ripening remain a matter of conjecture, but loss of berry water under highly evaporative conditions of late summer is a likely contributor.     

Auxin treatment of pre‐veraison grape (Vitis vinifera L.) berries both delays ripening and increases the synchronicity of sugar accumulation

Background and Aims: Pre‐veraison auxin treatments can delay grape berry ripening, but there is little information about their effects on berry development and wine composition. The aim of this study was to further investigate these effects and explore the practical implications of delaying ripening. Methods and Results: Treatment of pre‐veraison Vitis vinifera L. cv. Shiraz berries with 1‐naphthaleneacetic acid (NAA) significantly delayed ripening as measured by the accumulation of total soluble solids (TSS) and anthocyanins. The onset of the post‐veraison phase of berry size increase was delayed in NAA‐treated fruit, but these fruit were significantly larger than Control fruit at harvest. NAA‐treatments significantly increased the synchronicity of berry sugar accumulation. GC‐MS analysis of wine headspace volatiles showed significant, but largely small, differences in the concentration of 19 compounds. No significant difference in sensory properties was found between replicate small‐scale wine lots made from Control and NAA‐treated fruit. Conclusions: Auxin treatment delayed berry ripening, increased the synchronicity of sugar accumulation between berries, increased berry size and changed the levels of some volatile compounds, but did not affect wine sensory properties. Significance of the Study: We propose that NAA sprays might be used to delay grape berry ripening and increase the synchronicity of sugar accumulation, and therefore ripening, without deleterious effects on wine quality. This may be useful in controlling winery intake and fruit composition.     

Effect of pre‐ and post‐veraison water deficit on proanthocyanidin and anthocyanin accumulation during Shiraz berry development

Background and Aims: Water deficit is known to influence berry development as well as flavonoid metabolism. The aim of this study was to investigate the influence of pre‐ and post‐veraison water stress on the proanthocyanidin and anthocyanin accumulation on berry samples selected at comparable physiological maturity, especially after veraison while avoiding sugar influence. Methods and Results: Three irrigation treatments were applied by a drip irrigation system on three rows of 30 vines from an experimental Shiraz vineyard. Pre‐veraison water stress had no effect on total proanthocyanidin accumulation but increased accumulation of all anthocyanins except malvidin and p‐coumaroylated derivatives, whereas post‐veraison water stress enhanced the overall anthocyanin biosynthesis, particularly malvidin and p‐coumaroylated derivatives. Conclusions: Pre‐ and post‐veraison water stress affected the anthocyanin composition differently, suggesting a differential regulation of the genes involved in the last steps of anthocyanin biosynthesis pathway. Significance of the Study: The study identifies the effect of pre‐ and post‐veraison water stress while avoiding sugar influence on anthocyanin accumulation which could be maximised since both stresses differently impacted hydroxylation and methylation of anthocyanins.     

Developmental variation in sensitivity of Vitis vinifera L. (Shiraz) berries to soil water deficit

A large-scale, long-term irrigation experiment was established near Waikerie in the South Australian Riverland to investigate the feasibility of controlling berry size and ripening at the vineyard scale with modern irrigation systems. Irrigation treatments were devised to impose water stress, by withholding irrigation, during four periods of berry development after flowering of Vitis vinifera (variety Shiraz). Varying water deficits were achieved during each period and between the four seasons, which were climatically diverse. In one season water deficit during the period after flowering resulted in the greatest reduction in berry weight compared with that of well-watered vines, however, in another, water deficit during this period had no effect on berry weight. By comparison, berries appeared to be insensitive to water deficit during the month before harvest in all four seasons. A soil water deficit index was derived to compare the varying levels of water deficit between treatments and seasons on berry development. Deficit effects on berry development were assessed using either comparative growth rate or berry weight near harvest. Regression analysis of berry development against soil water deficit indicated that berries were most sensitive to water stress during the post flowering period.     

Fruit-set on small Chardonnay and Shiraz vines grown under varying temperature regimes between budburst and flowering

Small Chardonnay and Shiraz vines were grown under controlled conditions at 25°/20°C day/night temperatures but transferred for one week to 17°/14°C or 12°/9°C at four stages of growth between budburst and flowering. In Chardonnay, half the vines were given supplementary pollination with pollen produced under favourable conditions. Per cent fruit-set and berry number per bunch of Chardonnay were reduced by about one third to one half by 12°/9°C, applied just before and at the early stage of flowering. At these stages, and with this low-temperature treatment, supplementary pollination had significant positive effects. Total seed number per berry was not affected by treatment, but the proportion of hollow seeds increased in the treatments which suffered reduced set. This resulted in a positive relation between the number of functional seeds per berry and the number of berries per bunch. In Shiraz, the differences between the various treatment means were small and mostly not significant. It is concluded that the reduction in fruit-set of Chardonnay due to cool temperatures near flowering is due to detrimental effects on both pollen and ovules.     

ABA during reproductive development in non-irrigated grapevines (Vitis vinifera L. cv. Tempranillo)

In grapevines, stomatal aperture decreases after a mid-morning peak during summer days. Afternoon stomatal closure increases in non-irrigated plants as water limitation progresses, which suggests the involvement of abscisic acid (ABA) in the control of stomatal aperture. The objective of this work was to study the seasonal and diurnal time-courses of CO₂ assimilation rate, leaf conductance, leaf water potential +, and ABA concentration in xylem sap, leaves, flowers and berries in non-irrigated field-grown Tempranillo grapevines throughout reproductive development. Leaf decreased throughout fruit development because water availability decreased towards the end of the reproductive cycle. CO₂ assimilation rate, leaf conductance and xylem ABA concentration also decreased during the course of the growing season. Combining all measurements xylem ABA was either not correlated, or only slightly correlated, with leaf water status + and daily leaf conductance, respectively. This lack of relationship indicates that xylem ABA during fruit ripening had functions other than provision of a non-hydraulic signal. On a seasonal basis, xylem ABA concentration measured in non-irrigated grapevines was well related to berry ABA concentration, especially at the end of fruit development (veraison and harvest).     

Effects of manipulated grape berry transpiration on post-veraison sugar accumulation

A series of experiments were conducted on container-grown Pinot Noir and Sangiovese grapevines ( Vitis vinifera L.) to investigate whether changes in berry water loss at veraison influence the pattern of sugar accumulation. Berry transpiration was induced to vary either by changing the vapour pressure deficit (VPD) around bunches through temperature or relative humidity (RH) manipulations, or by applying drying-accelerating emulsion or a hydrophobic coating (vaseline) over the berry skin. In all the experiments, every berry of every bunch was rated prior to treatment as to softness and colour intensity. Transpiration rates were derived either from measurements of attached bunches using a custom-built open gas-exchange system or from weight loss calculated for single excised berries. Berry development and ripening were monitored throughout each experiment as deformability, fresh weight, and sugar concentration and content. Berries either did not respond to VPD-enhancement or showed reduced water loss when bunches were subjected to high temperature. Low berry transpiration in the latter treatment led to lower sugar content per berry up to harvest, and berry transpiration and net sugar intake were linearly correlated up to 0.20–0.25 mmol/m².s. A similar correlation was found also in the coating experiment within the first five days after treatments. When berry transpiration was restricted by applying vaseline, sugar accumulation was retarded. Low values of VPD, induced by raising the RH around the bunches, lowered sugar concentration but not sugar content per berry. The present study provides preliminary evidence that sugar accumulation in grapevine berries responds to changes in the evaporative demand around the bunch at veraison.