Post-veraison Water Research Articles

Long-Term Study of the Crop Forcing Technique on cv. Tempranillo (Vitis vinifera L.) Vines and Suggested Irrigation Strategies to Improve Water Use Efficiency of Forced Vines

Recently, the crop forcing technique (summer pruning that “forces” the vine to start a new cycle) has proven to be effective in delaying the harvest date and increasing must acidity, but also reducing the yield. However, recent information on deficit irrigation strategies combined with the crop forcing technique reveals that the crop forcing technique reduces irrigation water use efficiency. Two experiments were conducted. Experiment 1 was a 4-year trial to test the effect of the forcing pruning date on the phenology, yield, yield components and water requirements when post-veraison water stress is applied. In this experiment, the treatments were unforced vines (UF-RDI) and forced vines with a forcing pruning date about 70 (F1-RDI) and 100 (F2-RDI) days after budburst. The harvest date was delayed 34 (F1) and 66 (F2) days increasing the must acidity and malic acid concentration in the forced treatments. However, both forced treatments had a reduced yield (36% in F1 and 49% in F2) and irrigation water use efficiency (12% in F1 and 65% in F2). Experiment 2 was a 2-year trial in which irrigation was suppressed before the forcing pruning in F1 (F1-Pre) and F2 (F2-Pre) and after veraison. The yield, yield components, must quality and irrigation were compared to forced vines with irrigation suppression only after veraison (F1-RDI and F2-RDI). For the entire experiment, both treatments in which irrigation was suppressed before the forcing pruning reduced the amount of irrigation supplied (10% in F1-Pre and 30% in F2-Pre) with no negative effects on the yield, yield components or must quality when compared to F-RDI treatments.

Cumulative response of Tempranillo vines to the crop forcing technique and pre-forcing and post-veraison water stress in terms of yield and grape and wine quality

Elevated temperatures during berry ripening are detrimental to grape quality. The crop forcing technique (summer pruning that ‘forces’ the vine to start a new cycle) increases must acidity and malic acid concentration at harvest by delaying the date of veraison. However, little information is available on the sensitivity to water stress of forced vines. A 3-year trial was conducted to test three irrigation strategies in forced vines: a minimum threshold of mid-day stem water potential (Ψs) of −0.75 MPa before forcing (DI), a minimum Ψs threshold of −1.2 MPa only after veraison (RDI), and the combination of both treatments (DI + RDI). Results were compared to a non-forced treatment with a minimum Ψs threshold of −1.2 MPa after veraison (C-RDI). Must acidity increased, and pH decreased in the forced treatments. However, yield was reduced by 35% and irrigation requirements increased by 20% when comparing forced and unforced treatments. As a result, water use efficiency was reduced in forced treatments. Only after a dry spring did the, DI (11%) and DI + RDI (30%) treatments, save water compared to the C-RDI treatment. Moreover, although Ψs before forcing never fell below −0.75 MPa, a significant negative correlation (R2 = 0.76) was found between the integral of water stress before the vines were forced and the number of forced bunches per vine. Post-veraison water stress in forced vines reduced the polyphenol content of the wine. Our findings suggest that forced vines are extremely sensitive to even mild water stress.

Water deficit before veraison is crucial in regulating berry VOCs concentration in Sangiovese grapevines.

The impact of water deficit on volatile organic compounds (VOCs) responsible for grape aroma remains quite unclear. The aim of this study was to evaluate the effect of different timing and intensity of water deficit on berry VOCs and on their biosynthetic pathways. Fully irrigated control vines were compared with the following treatments: i) two different levels of water deficit from berry pea-size through veraison, ii) one level of water deficit during the lag-phase, and iii) two different levels of water deficit from veraison through harvest. At harvest, total VOC concentrations were higher in berries of water stressed vines from berry pea size through veraison or during the lag phase, whereas post-veraison water deficit determined similar concentrations as control. This pattern was even more pronounced for the glycosylated fraction and was also observed for single compounds, mainly monoterpenes and C13-norisoprenoids. On the other hand, free VOCs were higher in berries from lag phase or post-veraison stressed vines. The significant glycosylated and free VOCs increment measured after the short water stress limited to the lag phase highlight the pivotal role played by this stage in berry aroma compound biosynthesis modulation. The severity of water stress before veraison was also important, since glycosylated VOCs showed a positive correlation with the pre-veraison daily water stress integral. The RNA-seq analysis showed a wide regulation induced by irrigation regimes on terpenes and carotenoids biosynthetic pathways. The terpene synthases and glycosyltransferases as well as genes of the network of transcription factors were upregulated, especially in berries from pre-veraison stressed vines. Since the timing and intensity of water deficit contribute to regulate berry VOCs, irrigation management can be used to achieve high-quality grapes while saving water.

Berry flavonoids are differently modulated by timing and intensities of water deficit in Vitis vinifera L. cv. Sangiovese.

In this work, we tested the effect of different regulated deficit irrigation (RDI) regimes on berry flavonoid content and its relative biosynthetic pathways. Vines were subjected to six irrigation regimes over two consecutive years: a) full irrigation during the entire irrigation period (FI); b) moderate (RDI-1M) or c) severe (RDI-1S) water deficit between berry pea-size and veraison; d) severe water deficit during the lag-phase (RDI-LS); and e) moderate (RDI-2M) or f) severe (RDI-2S) water deficit from veraison through harvest. Berries from both RDI-1 treatments showed the highest accumulation of anthocyanins, upregulating the expression of many genes of the flavonoid pathway since the beginning of veraison until harvest, far after the water deficit was released. Although to a lesser degree than RDI-1, both post-veraison water deficit treatments increased anthocyanin concentration, particularly those of the tri-substituted forms, overexpressing the F3'5'H hydroxylases. The moderate deficit irrigation treatments enhanced anthocyanin accumulation with respect to the severe ones regardless of the period when they were applied (pre- or post-veraison). The water deficit imposed during the lag-phase downregulated many genes throughout the flavonoid pathway, showing a slight reduction in anthocyanin accumulation. The measurements of cluster temperature and light exposure highlighted that under deficit irrigation conditions, the effects induced by water stress prevailed over that of light and temperature in regulating anthocyanin biosynthesis. Flavonol concentration was higher in RDI-1S berries due to the upregulation of the flavonol synthases and the flavonol-3-O-glycosyltransferases. In this case, the higher cluster light exposure induced by water deficit in RDI-1S berries had a major role in flavonol accumulation. We conclude that the timing and intensity of water stress strongly regulate the berry flavonoid accumulation and that proper management of deficit irrigation can modulate the phenylpropanoid and flavonoid pathways.

Deficit irrigation differently affects aroma composition in berries of Vitis vinifera L. (cvs Sangiovese and Merlot) grafted on two rootstocks

Background and Aims Water deficit modifies the concentration of the aroma compounds of grape berries, but little information is available on the effect of deficits applied at different phenological stages. We evaluated the effect of deficit irrigation on glycosylated volatile organic compounds (VOCs) responsible for the aroma of berries of Sangiovese and Merlot cultivars grafted on 1103P or SO4 rootstocks. Methods and Results Vines were subjected to either pre- or post-veraison water stress, and berry composition compared against that of fruit of fully irrigated vines. At harvest, a higher concentration of glycosylated VOCs was measured in berries from vines stressed pre-veraison, but while it increased as water deficit increased in Sangiovese, this occurred only at a low or moderate level of stress in Merlot. Post-veraison water stress had a negative or negligible effect on the concentration of glycosylated VOCs in berries at harvest. The rootstock affected the concentration of glycosylated VOCs, particularly in vines stressed pre-veraison, with higher glycosylated VOCs observed for SO4 grafted vines than for 1103P grafted vines. Conclusions Pre-veraison water deficit enhanced the concentration of berry glycosylated VOCs, while post-veraison deficit did not. The rootstock–scion interaction might amplify the irrigation effect on berry glycosylated VOCs. Significance of the Study Modifying the timing and volume of irrigation might allow management of berry flavour for improved fruit and wine composition. Irrigation protocols should be tailored for specific cultivar–rootstock combinations.

Post-Veraison Water Stress and Pruning Level on Merlot Grapevine (Vitis vinifera L.): Effects on Berry Development and Composition

The grapevine berry development and composition at harvest are major determinant of productivity and wine quality. The increase in grapevine productivity by applying proper pruning and watering may affect fruit traits of the grapevine development notably berry size, weight, and volume as well as the berry composition mainly the total soluble solids (TSSs), titratable acidity (TA), pH of the grapes, total anthocyanins, and phenolic content and concentration. In this context, this study aimed to explore the response of berry development and composition to the interactive effect of pruning level and post-veraison water stress. Four pruning levels (severe, standard, light, and minimal) in combination with four post-veraison water stresses (none, light, moderate, and intense) were tested. The interactive effect of pruning level and post-veraison water stress has significantly altered all parameters, except berry weight which was influenced by the main effect of the two factors. Generally, post-veraison water stress reduced berry volume, weight, yield, and TA, but increased the TSS, pH, total anthocyanins, and phenols. Increasing in the pruning level also reduced berry yield per vine, TSS, and pH, but increased the berry volume, weight, TA, total anthocyanins, and phenols. Specifically, the highest berry volume, weight, and TA were registered in severely pruned grapevines with adequate water supply. Conversely, the minimally pruned grapevines with intense water stress had the highest TSS and pH of grape juice. The total anthocyanins and phenols were advanced by the increment from minimal to severe pruning levels but depressed when the water stress extended from none to an intense level. In the other hand, the maximum total anthocyanins and phenols in terms of concentration and content were observed in severely pruned grapevines under intense water stress. Interestingly, higher berry yield per grapevine was scored in minimally pruned grapevines with adequate water supply, possibly due to the increased number of nodes per vine. TSS had a strong negative relationship with berry volume, weight, yield, and TA, while pH had a strong positive relationship with TSS. Total anthocyanins and phenols were also inversely correlated with berry yield per grapevine. The results showed that the combined effect of pruning levels and water stress is a powerful tool to balance berry development and composition. As Merlot is a typical red wine grapevine, it is important to increase the berry composition even though there could be a reduction in its berry development variables including berry yield per vine.

The effect of regulated deficit irrigation on growth, yield, and berry quality of grapevines (cv. Sangiovese) grafted on rootstocks with different resistance to water deficit

The aim of this work was to investigate the effect of full irrigation (FI), pre-veraison water deficit (RDI 1), or post-veraison water deficit (RDI 2) on growth, yield, and berry quality in container-grown, mature vines of cv. Sangiovese grafted onto either 1103P or SO4 rootstock over two consecutive growing seasons. Deficit irrigation regimes significantly affected vine water status of both rootstocks before and after veraison. Trunk diameter (TD) increment was markedly affected when water was restricted early, but not in the post-veraison period. Deficit irrigation from fruit set to veraison inhibited vegetative growth (TD, canopy volume, and weight of pruned wood) more than that applied from veraison to harvest. Yield was unaffected by either irrigation or rootstock in both years. Irrigation had a marked effect on berry and juice quality: the RDI 1 treatment induced the highest berry anthocyanin concentration, and the lowest titratable acidity (TA), which, instead, increased in the RDI 2 treatment. RDI treatments did not modify berry dry weight, soluble solid content, TA, anthocyanins, and epicarp total phenols in vines on both rootstocks.

Differences among two grapevine cultivars in their response to pre and post veraison water deficit

Differences among two grapevine cultivars in their response to pre and post veraison water deficit

Texture properties and phenol extractability indices of the grape berry under pre- and post-veraison water deficit (Vitis vinifera L. 'Kékfrankos')

Optimal water supply is one of the most important factors in quality wine making. However, water availability is limited in several wine regions and water shortage is getting even worse due to climate change, especially under arid climate conditions. Therefore, proper water management of the vineyards, the amount and the timing of irrigation will play a crucial role in sustainable viticulture in the near future. In this study, the effect of timing of moderate water deficit on berry texture characteristics and phenolic maturity were investigated. 'Kekfrankos' grapevines were submitted to different water regimes: moderate water deficit from berry set until veraison (WD1), moderate water deficit from veraison until harvest (WD2), no water deficit (C). Concentration of the phenolic components of the grape berry skins and berry mixture for the Glories indices were measured by spectrophotometer (UVmini-1240 CE UV-VIS, Shimadzu, Japan). Cell and seed maturity indices (CMI%, SMI%) were also calculated. Berry texture characteristics were monitored by a TA.XT Plus Texture Analyser (Stable Micro System, UK). Berry skin and seed texture properties were affected by water regimes. Skin and seed hardness of WD1 were significantly lower than those of WD2. Significant differences were found in berry hardness between the treatments (C>WD1>WD2). Berry gumminess, resilience and chewiness of WD2 were lower compared to C and WD1. Anthocyanin extractability was higher when plants were not subjected to post-veraison water limitations (WD1). Furthermore, the seed maturity index was lower when water deficit occurred between berry set and veraison. Pre-veraison water deficit resulted in delayed ripening, softer seeds and thus higher phenol extractability compared to WD2 and C. Late seasonal water deficit resulted in thicker skins, which was accompanied by lower anthocyanin extractability than in WD1 and C. It seems that anthocyanin extractability is influenced by the actual water status of the grapevine rather than skin textural properties. However, there are some connections between skin texture parameters and maturity indices.

Eco-Physiological Traits and Phenylpropanoid Profiling on Potted Vitis vinifera L. cv Pinot Noir Subjected to Ascophyllum nodosum Treatments under Post-Veraison Low Water Availability

In Mediterranean regions, extreme weather conditions during the growing season may alter grapevine physiology and metabolism, thus modifying the quality of wines. The objective of this study was to investigate the effects of Ascophyllum nodosum treatments on plant physiology and berry metabolism in Vitis vinifera exposed to water stress. The experiment was performed on potted vines subjected to two irrigation regimes (well-watered, WW, and water stressed, WS) both associated with A. nodosum treatments (SWE), compared with control plants (CTRL). Gas exchanges, chlorophyll fluorescence, and water relations were monitored on SWE and CTRL leaves, both in WW and WS vines at three times. Moreover, the quantification of secondary metabolites and their partitioning were performed in berry skins. Plants treated with A. nodosum extract showed higher photosynthesis and stomatal conductance than CTRL in both irrigation regimes and maintained a better plant hydraulic conductivity at the end of the sampling period. In addition, secondary metabolites in berry skins and their partitioning were significantly affected by the treatments in both irrigation regimes. Our results suggest that foliar application of A. nodosum extract may help the acclimation of grapevines to post-veraison water stress, likely improving plant physiological and biochemical performances under environmental constraints.

Effects of pre and post-veraison water deficit on Vermentino cluster microclimate and berry composition

The influence of light and thermal microclimate on berry quality of a Vermentino vineyard, managed with deficit irrigation strategies in north-western Sardinia, was analyzed. Two water deficit, pre- (ED) and post-veraison (LD), an irrigation (IC) and a non-irrigation (NC) control treatments were compared during berry development. Grapevine performances were evaluated by analyzing leaf gas exchange, source-sink balance, light and thermal microclimate effects on berry composition. Early and/or late deficit irrigation following a mild to moderate water stress threshold enabled high leaf physiological performances. Though with high stomatal conductance sensitivity to water deficit and anisohydric behavior, this variety exhibited high assimilation rate and quick recovery capacity after enduring moderate and severe water stress. All treatments achieved satisfactory sugar and acidic levels. Berry phenols were higher in LD due to lower canopy coverage and better light conditions compared to IC. Up to mid-ripening, cluster exposure to elevated temperatures negatively influenced phenolic accumulation, mostly in NC and to a lower extent in ED. In the last ripening weeks, total phenols was majorly influenced by light interception.

Chemical and sensory characteristics of Gaglioppo wines obtained from grapes grown under two different water regimes

Climate change can affect the crops production capacity and modify the water requirements in the different regions of the world. In particular, in southern Europe and in the Mediterranean region the vegetative cycle of plants will take place in a warmer and drier period, with the consequent increase in vegetative activity, transpiration rate, and water consumption. In the case of vine, the rationalization of water resource needs a deep knowledge of the complex relationships between climate, soil, water availability and grape variety, in order to preserve the high quality regional wine productions. In the Cirò DOC area (Calabria), the effect of irrigation, prolonged until maturity, on the polyphenolic content of the grapes was studied with the Gaglioppo red grapes variety, in order to verify whether a moderate post-veraison water supply could favour the completion of phenolic maturation. Two different water regimes were compared in the vineyard, and the physicochemical composition, the polyphenolic and aromatic profiles and the sensory characteristics of the resulting wines were studied. The study confirmed that the climatic variability of the different vintages can influence both the vegetative-productive activity of vines and the effect of water supplies.

Water Deficit Synchronizes Berry Color Development in Crimson Seedless Table Grapes

Crimson Seedless is one of the most important table grape cultivars in the world, but often exhibits uneven berry color when grown in warm climates. Deficit irrigation is used extensively by growers during the ripening phase to advance fruit maturity and color, but there is a lack of information about the relationship between irrigation practices and fruit ripening variability. We imposed deficit irrigation in a commercial Crimson Seedless vineyard in the Maipo Valley, Chile, from veraison to harvest in two consecutive seasons. The fruit was tested for uniformity of Brix, firmness, and the color parameters “L”, “a”, “b”, and the Color Index of Red Grapes using analysis of variance on absolute residuals (Levene’s test). Postveraison water stress increased water productivity, Brix, and slightly improved berry coloration, but did not affect berry weight, size, or firmness. Moderate levels of water stress improved color uniformity at harvest, as lower values of leaf water potential were associated with a lower percentage of green berries that never matured. These results confirmed the role of deficit irrigation in the table grape ripening process. In contrast, extending the fruit ripening period by delaying harvest beyond 18 Brix did not increase color accumulation, but did increase berry shatter.

Grape Metabolic Response to Postveraison Water Deficit Is Affected by Interseason Weather Variability.

Postveraison water deficit is a common strategy implemented to improve fruit composition in many wine-growing regions. However, contrasting results are often reported on fruit size and composition, a challenge for generalizing the positive impact of this technique. Our research investigated the effect of water deficit (WD) imposed at veraison on Merlot grapevines, during two experimental seasons (2014-2015). In both years WD resulted in reduced carbon assimilation rates and leaf shedding. However, the treatment effect on the analyzed berry parameters varied between seasons. Modification of skin metabolites was more evident in 2015 than in 2014, despite the similar soil water content and water stress physiological parameters (gas exchange, water potential) recorded in the two experimental years. Higher solar radiation and air temperature in 2015 than in 2014 hint for the involvement of atmospheric parameters in fulfilling the potential effect of WD. Our results suggest that the interaction between water availability and weather conditions plays a crucial role in modulating the grape berry composition.

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.

The effect of postveraison water deficit on the phenolic composition and concentration of the Kékfrankos (Vitis vinifera L.) berry

The effect of moderate and severe water deficit was examined on berry skin phenolic concentration and composition of the Kékfrankos variety (Vitis vinifera L.). Moderate water stress induced higher concentration of anthocyanin derivatives compared to the non-stressed plants with, the exception of Cya-3-g. Concentrations of some anthocyanin derivatives (Mal-3-g and Peo-3-g) were also higher in the severely stressed berry skins than in the control berries. No differences were found between the stressed and the non-stressed plants in the case of Cya-3-g. Similarly, concentration of some phenolic components (ie. protocatechuic acid, gallic acid, vanillic acid, trans-resveratrol etc.) increased as a result of water deficit. On the other hand, others such as quercetin-3-glucuronide decreased as the water deficit increased. In general, water deficit had a beneficial effect on grape phenolic concentration; however it can be modified by the changes in berry skin/flash ratio.

The effects of pre- and post-veraison water stress on growth and physiology of potted Pinot Noir grapevines at varying crop levels

The interactions of water stress timing and crop level on growth, gas exchange, water relations and ripening of potted Pinot Noir grapevines were examined. Pre-veraison water stress induced a greater reduction of shoot and berry growth and a more rapid limitation of net photosynthesis (Pn) and stomatal conductance (g(s)) as compared to post-veraison stress. At the end of stress, when mid-day and pre-dawn leaf water potential were below -1.1 and -0.6 MPa, the reduction in Pn of stressed vines was more marked in the 2- and 4-cluster plants versus 1-cluster plant. Crop level had almost no significant effects on gas-exchange, growth and ripening and but few interactions with timing of water stress. These responses seem to reflect the high leaf area-to-fruit ratios at each crop level which probably buffered the effects of reduced leaf function induced by water stress.

Comparison of whole-canopy water use efficiency and vine performance of cv. Sangiovese (Vitis vinifera L.) vines subjected to a post-veraison water deficit

In the present paper a series of WUE expressions, including the physiological and agronomical, were compared in potted cv. Sangiovese (Vitis vinifera L.) grapevines which were either well watered (WW) or subjected to progressive post-veraison water stress (WS) by supplying decreasing fractions (i.e. 70%, 50% and 30%) of daily canopy transpiration (Tc) concurrently recorded via a plant-enclosure gas exchange system. While single-leaf intrinsic water-use efficiency (WUEi) increased with water stress severity, seasonal whole-canopy WUE were similar at pre-stress, 70% Tc, and upon rewatering but dropped during severe water stress. WUE calculated as mass of dry weight stored in annual biomass (leaves, canes and clusters) per liter of water used, did not differ on a seasonal basis, whereas WW and WS showed similar grape composition despite the latter suffered a 25% yield reduction. Results confirm that whole-canopy WUE is a much better index than single-leaf based WUE parameter for extrapolation to agronomic WUE and actual grape composition. Under our specific case study, due to high reactivity of Sangiovese to early yellowing and shedding of basal leaves, it can be recommended that post-veraison water supply to Sangiovese vines should not be lower than 70% of daily vine water use.

Effects of postveraison water regime on the phenolic composition of grapes and wines of cv. Agiorgitiko (<em>Vitis vinifera</em> L.)

<p style="text-align: justify;"><strong>Aims</strong>: Vine water deficit is widely accepted as a powerful means to control grape and wine attributes. However, quality improvement is often achieved at the expense of a reduction in yield, especially when water deficit conditions are applied during the preveraison period. The aim of the present work was to test an irrigation regime based on manipulating water availability from veraison to harvest, as a means to control berry and wine composition with minimum effect on reproductive growth parameters.</p><p style="text-align: justify;"><strong>Methods and results</strong>: A field trial was conducted during two consecutive years (2007-2008) in Nemea, Southern Greece. Three irrigation treatments were applied on seven-year-old, vertical shoot positioned and spur pruned Agiorgitiko vines (<em>Vitis vinifera</em> L.), from veraison through harvest : irrigation at 70 % of crop evapotranspiration (ET<sub>c</sub>) (I70), irrigation at 30 % of ET<sub>c</sub> (I30) and non irrigated (NI). Irrigation amount produced significant differences in postveraison midday stem water potential pattern, especially during the drier year 2008. Yield was increased by irrigation in 2008, whereas berry growth was unaffected in both seasons. Berries of NI vines achieved higher total skin anthocyanin content in 2007, although individual anthocyanin levels were not affected by water regime. Irrigation effect on skin tannins was inconsistent but seed tannins were higher in I70 vines, with increased levels of catechin and epicatechin monomers. Among wine attributes, tannin concentration, but not anthocyanin, was mostly responsive to water deficit-induced changes in berry phenolic composition. The wines made from I70 grapes had a higher tannin content than those made from NI grapes.</p><p style="text-align: justify;"><strong>Conclusions</strong>: The results presented show that postveraison water regime had a significant effect on skin anthocyanins and, more markedly, on seed tannins, without altering berry growth parameters. Especially for seed tannins, this effect appears to predominate over variations in climatic conditions between years.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: This trial suggests that Agiorgitiko vines grown on the loamy soils of Nemea perform better under non irrigated conditions during the postveraison period since rainfed vines had improved phenolic composition (higher colour with lower contribution of seed tannins) without significant loss in productivity.</p>

Yield components and grape composition responses to seasonal water deficits in Tempranillo grapevines

A field experiment was carried out over three seasons on Vitis vinifera cv. Tempranillo in order to compare pre-veraison and post-veraison water restrictions on vine performance and fruit composition. Rain-fed vines were compared with a treatment named MAX that was constantly irrigated at 75 % of the estimated crop evapotranspiration (ETc). In addition, an early (pre-veraison) water deficit strategy (ED) was applied by withholding irrigation until plant water stress experienced by vines surpassed a threshold value of midday stem water potential of −1.0 MPa. After that, 75 % of ETc was applied. A late season deficit (LD) treatment was irrigated as per the MAX up to veraison, and thereafter, water application was reduced to approximately 37 % of ETc. All irrigation regimes increased vine yield up to 58 % with respect to the rain-fed treatment, and no differences in yield among the irrigated treatments occurred. However, there were differences in berry composition among the different irrigation strategies. The ED strategy was more effective than the LD one in reducing berry growth leading to more concentrated berries in terms of sugars and anthocyanins. The LD water shortage impaired berry sugar accumulation due to the detrimental effect of water stress on leaf photosynthesis.