**2.2 Effects of vine water status on vegetative growth**

Plant growth is strongly affected by water availability. Freeman and Smart [29] reported increases in root growth under water deficit conditions, while Van Zyl [30] indicated that irrigating vines after 25 or 50% of the total water available had been used up by around the time of flowering led to 190 and 300 actively growing root tips/m2 , respectively. However, this was reduced to 40 root tips/m2 when the soil was irrigated after 75% of the total water available had been consumed. Prolonged exposure to moderate water deficit thus increases the root-to-shoot ratio [4], but both severe water deficit and irrigation that keep the soil close to saturation for long periods negatively affect root growth.

There is, however, no evidence that vegetative growth in vines is increased under water deficit conditions. Indeed, water deficit negatively affects the vegetative growth of vine trunks, shoots and leaves. However, the limitation of vegetative growth depends on the timing, duration and severity of water deficit. The most active period of vegetative growth takes place between budbreak and veraison [12], with a maximum reached at the beginning of the growth cycle some 60 days after budbreak [6, 31–33]. Growth then progressively decreases until a vegetative standstill is reached close to the time of veraison.

After budbreak, shoot growth occurs at the expense of reserves stored during previous vegetative cycles [34]. In Mediterranean-type climates, it is uncommon for soil water deficits to be strong enough to inhibit the growth of shoots during this initial growth phase (rain usually falls during this period, and there is still winter rain stored in the soil [35]), although total needs up to veraison are rarely so easily met.

The effect of water deficit on the canopy has been widely studied. Many authors indicate it to reduce shoot growth and canopy development [6, 11, 36–40], a consequence of reduced activity in the shoot terminal meristem [41], reduced leaf area [42] and the senescence and fall of the basal leaves. Physiological changes in the vine, such as reduced leaf photosynthetic activity in response to stomatal closure due to water stress, have been studied in many experiments [4, 22, 43–52].

Post-veraison water stress has little or no effect on shoot growth [22, 53, 54]. Nevertheless, severe water stress during the ripening period can significantly diminish leaf area due to early senescence [55]. During the postharvest period, root growth and nutrient absorption contribute towards the accumulation of reserve carbohydrates. This period is important for the vigour and productivity of the vine

**79**

productivity under water stress.

*Effects of Vine Water Status on Yield Components, Vegetative Response and Must and Wine…*

the accumulation of carbohydrates but avoid the regrowth of laterals [56]. Shellie [9] and Greenspan [57] reported a reduction in the main shoot growth from 20 days after budbreak when the midday leaf water potential approached—1.0 MPa in cvs. Merlot, Cabernet Sauvignon and Pinot Gris vines. Munitz et al. [58] observed a reduction in leaf area in cv. Merlot after continuous irrigation at 20, 35 and 50% of the ETc, reaching maximum ψstem values of −1.2, −1.3 and −1.4 MPa during cluster closure to veraison. However, in cv. Cabernet Sauvignon, Acevedo-Opazo [59] reported no differences neither in shoot length, number of stems, internode length or pruning weight between three treatments in which the midday ψstem was maintained at between −0.8 and −0.95 MPa, −1.0 and −1.2 MPa and −1.25 and −1.4 MPa, from post-setting to harvest—although in that work ψstem did reach values of −1.0 MPa close to veraison. Water stress induced at the beginning of the growing season (flowering to cluster closure or earlier) may thus result in a reduction in canopy size. Under field conditions, however, severe water stress might be hard to induce; soils will normally contain some stored water. In another experiment on cv. Cabernet France [36], less shoot growth was observed in an early water deficit treatment compared to control, although the leaf water potential values reached were similar (≈−0.8 MPa). The authors [36] suggested that this level of water deficit was not responsible for the reduced shoot length observed, but to the early limitation of photoassimilates, probably caused by a reduction in the hydraulic conductivity of the wood through prolonged exposure to early water

in the following season. The soil water content aimed for at this time should ensure

This high sensitivity of shoot growth to water deficit has sometimes been used as an early indicator of the latter (based on allometric measurements). Pellegrino et al. [61] analysed the effects of water deficit on certain components of shoot vegetative growth (the number of leaves to emerge on the first- and second-order laterals, leaf area, internode length of each phytomer on the first-order laterals and the frequency of second-order laterals) in cv. Shiraz. Sensitivity to water deficit was seen to increase as the second-order laterals emerged, i.e. the rate of emergence of second-order laterals decreases in response to water deficit. These authors also established a water deficit indicator (ratio of branching intensity between first- and second-order laterals) that was sensitive to slight water deficit—even more so than the stomatal response. A more recent study showed significant changes in the abundance of proteins involved in translation, energy production, antioxidant defence and steroid metabolism during early growth and indicates these changes to occur before any detectable reduction in

The availability of water in the soil leads to differences in hydraulic conductivity that leave permanent marks on vine plant organs. At the trunk level, high water availability early in the season results in wider xylem vessels (and therefore greater hydraulic conductivity) and greater trunk diameter, ring width and ring area. Also, when vines are subjected to late water deficit, they show more negative water potential values at the end of the season than do vines that receive low-level but relatively constant irrigation [60]. Thus, high water availability during the vegetative growth of *Vitis* increases vessel diameter and hydraulic conductivity, leaving plants more vulnerable to stress during the ripening period [60]. However, at the shoot level, Pagay et al. [63] reported xylem vessels with larger diameters to be more resistant to cavitation, concluding that they have less inter-vessel pitting. This would result in a hydraulic advantage allowing them to better maintain growth and

Finally, pruning weight is linearly related to the amount of water applied and is less influenced by the timing of the water supply than is leaf area (**Figure 4**) [33, 64]. Reductions in shoot weight are accentuated by long-term water deficit [6]. Thus,

*DOI: http://dx.doi.org/10.5772/intechopen.87042*

deficit repeated over many seasons [60].

shoot elongation, stomatal conductance or photosynthesis [62].

#### *Effects of Vine Water Status on Yield Components, Vegetative Response and Must and Wine… DOI: http://dx.doi.org/10.5772/intechopen.87042*

in the following season. The soil water content aimed for at this time should ensure the accumulation of carbohydrates but avoid the regrowth of laterals [56].

Shellie [9] and Greenspan [57] reported a reduction in the main shoot growth from 20 days after budbreak when the midday leaf water potential approached—1.0 MPa in cvs. Merlot, Cabernet Sauvignon and Pinot Gris vines. Munitz et al. [58] observed a reduction in leaf area in cv. Merlot after continuous irrigation at 20, 35 and 50% of the ETc, reaching maximum ψstem values of −1.2, −1.3 and −1.4 MPa during cluster closure to veraison. However, in cv. Cabernet Sauvignon, Acevedo-Opazo [59] reported no differences neither in shoot length, number of stems, internode length or pruning weight between three treatments in which the midday ψstem was maintained at between −0.8 and −0.95 MPa, −1.0 and −1.2 MPa and −1.25 and −1.4 MPa, from post-setting to harvest—although in that work ψstem did reach values of −1.0 MPa close to veraison. Water stress induced at the beginning of the growing season (flowering to cluster closure or earlier) may thus result in a reduction in canopy size. Under field conditions, however, severe water stress might be hard to induce; soils will normally contain some stored water. In another experiment on cv. Cabernet France [36], less shoot growth was observed in an early water deficit treatment compared to control, although the leaf water potential values reached were similar (≈−0.8 MPa). The authors [36] suggested that this level of water deficit was not responsible for the reduced shoot length observed, but to the early limitation of photoassimilates, probably caused by a reduction in the hydraulic conductivity of the wood through prolonged exposure to early water deficit repeated over many seasons [60].

This high sensitivity of shoot growth to water deficit has sometimes been used as an early indicator of the latter (based on allometric measurements). Pellegrino et al. [61] analysed the effects of water deficit on certain components of shoot vegetative growth (the number of leaves to emerge on the first- and second-order laterals, leaf area, internode length of each phytomer on the first-order laterals and the frequency of second-order laterals) in cv. Shiraz. Sensitivity to water deficit was seen to increase as the second-order laterals emerged, i.e. the rate of emergence of second-order laterals decreases in response to water deficit. These authors also established a water deficit indicator (ratio of branching intensity between first- and second-order laterals) that was sensitive to slight water deficit—even more so than the stomatal response. A more recent study showed significant changes in the abundance of proteins involved in translation, energy production, antioxidant defence and steroid metabolism during early growth and indicates these changes to occur before any detectable reduction in shoot elongation, stomatal conductance or photosynthesis [62].

The availability of water in the soil leads to differences in hydraulic conductivity that leave permanent marks on vine plant organs. At the trunk level, high water availability early in the season results in wider xylem vessels (and therefore greater hydraulic conductivity) and greater trunk diameter, ring width and ring area. Also, when vines are subjected to late water deficit, they show more negative water potential values at the end of the season than do vines that receive low-level but relatively constant irrigation [60]. Thus, high water availability during the vegetative growth of *Vitis* increases vessel diameter and hydraulic conductivity, leaving plants more vulnerable to stress during the ripening period [60]. However, at the shoot level, Pagay et al. [63] reported xylem vessels with larger diameters to be more resistant to cavitation, concluding that they have less inter-vessel pitting. This would result in a hydraulic advantage allowing them to better maintain growth and productivity under water stress.

Finally, pruning weight is linearly related to the amount of water applied and is less influenced by the timing of the water supply than is leaf area (**Figure 4**) [33, 64]. Reductions in shoot weight are accentuated by long-term water deficit [6]. Thus,

*Advances in Grape and Wine Biotechnology*

**2.2 Effects of vine water status on vegetative growth**

*Shrivelling and weight loss in cv. Graciano grapes during late ripening.*

periods negatively affect root growth.

still is reached close to the time of veraison.

Plant growth is strongly affected by water availability. Freeman and Smart [29] reported increases in root growth under water deficit conditions, while Van Zyl [30] indicated that irrigating vines after 25 or 50% of the total water available had been used up by around the time of flowering led to 190 and 300 actively growing root

was irrigated after 75% of the total water available had been consumed. Prolonged exposure to moderate water deficit thus increases the root-to-shoot ratio [4], but both severe water deficit and irrigation that keep the soil close to saturation for long

water deficit conditions. Indeed, water deficit negatively affects the vegetative growth of vine trunks, shoots and leaves. However, the limitation of vegetative growth depends on the timing, duration and severity of water deficit. The most active period of vegetative growth takes place between budbreak and veraison [12], with a maximum reached at the beginning of the growth cycle some 60 days after budbreak [6, 31–33]. Growth then progressively decreases until a vegetative stand-

There is, however, no evidence that vegetative growth in vines is increased under

After budbreak, shoot growth occurs at the expense of reserves stored during previous vegetative cycles [34]. In Mediterranean-type climates, it is uncommon for soil water deficits to be strong enough to inhibit the growth of shoots during this initial growth phase (rain usually falls during this period, and there is still winter rain stored in the soil [35]), although total needs up to veraison are rarely

The effect of water deficit on the canopy has been widely studied. Many authors indicate it to reduce shoot growth and canopy development [6, 11, 36–40], a consequence of reduced activity in the shoot terminal meristem [41], reduced leaf area [42] and the senescence and fall of the basal leaves. Physiological changes in the vine, such as reduced leaf photosynthetic activity in response to stomatal closure due to water stress, have been studied in many experiments [4, 22, 43–52].

Post-veraison water stress has little or no effect on shoot growth [22, 53, 54]. Nevertheless, severe water stress during the ripening period can significantly diminish leaf area due to early senescence [55]. During the postharvest period, root growth and nutrient absorption contribute towards the accumulation of reserve carbohydrates. This period is important for the vigour and productivity of the vine

when the soil

, respectively. However, this was reduced to 40 root tips/m2

**78**

tips/m2

**Figure 3.**

so easily met.

#### **Figure 4.**

*Leaf area per vine at ripening (green bars) and winter pruning weight (blue line) from rainfed vines and three irrigation treatments applying 25, 50 and 100% of vine evapotranspiration (ETc) in averaged over four seasons in* cv. *Tempranillo. After [64].*

water deficit has a cumulative effect, probably due to reduced starch and sucrose accumulation in the perennial organs [65–67]. This is important since the sugars accumulated in the trunk and roots are the first carbohydrates to be used during the following spring's growth.

#### **2.3 Effects of vine water status on must and wine composition**

### *2.3.1 Effects of irrigation on total soluble solids*

Total soluble solids (TSS) accumulate in the berry during phase III of berry growth. The increase in sugar content (°Brix) is coupled with a resumption in berry growth, accompanied by a sharp increase in berry weight (**Figure 5**). At the beginning of ripening, sugar accumulation occurs through leaf photosynthesis and through the mobilisation of reserves [68] although this mobilisation soon ceases. Sugar is transported from leaves to the berry via phloem in the form of sucrose. Once in the berry, it is changed into glucose and fructose, the ratio between them remaining close to 1:1 throughout ripening [2]. Since the TSS content is directly related to leaf photosynthetic activity [2, 69], sugar content can be used to indirectly evaluate the plant photosynthesis activity. At the end of ripening, photoassimilates also divert to the fruit and to reserve tissues in the perennial parts of the plant [68].

A linear relationship exists between berry size and TSS (**Figure 6**). Thus, berry size provides a meaningful, inexpensive means of estimating plant activity and tracking ripening. At the end of the ripening period, the increase in berry weight levels off, and the discharge of sugar into the berry ends. When the berries reach maximum TSS due to photosynthesis, ripening is finished. The final °Brix may differ depending on variety, cultivation practices and climate.

The amount of available water influences both the sugar accumulation rate and berry size. Studies have shown that, under water deficit conditions, °Brix increases faster than under high soil water conditions (**Figures 5** and **6**). This means that for the same berry weight, the °Brix reached in rainfed vines (or grown under water deficit conditions) is higher than those reached in well-irrigated vines [33, 71]. However, sugar accumulation expressed on a per-berry basis is higher for irrigated vines. Since irrigated vines produce higher yields than either moderately water

**81**

**Figure 6.**

**Figure 5.**

*Unpublished data.*

*Effects of Vine Water Status on Yield Components, Vegetative Response and Must and Wine…*

stressed or nonirrigated vines, the sugar concentration of the berries produced under the former conditions increases slower, but finally they can get the same

*Seasonal change in 100-berry weight in cv. Merlot in two shoot load treatments. Compact circles represent a shoot load of 12 shoots per metre of row; open circles represent minimal pruning conditions.* 

*Change in the relationship between berry size and TSS under three irrigation regimens in cv. Cabernet sauvignon in Madrid (Spain). T1: rainfed (Y = 0.37x − 9.0R2 = 0.50\*), T2: irrigated 0.4·ETo (Y = 23.2Ln(x) − 85.12R2 = 0.68\*\*), T3: irrigated 0.2·ETo (Y = 0.40x − 15.82R2 = 0.71\*\*) [70].*

*DOI: http://dx.doi.org/10.5772/intechopen.87042*

concentration if they remain in the vine (**Figure 6**) [71].

*Effects of Vine Water Status on Yield Components, Vegetative Response and Must and Wine… DOI: http://dx.doi.org/10.5772/intechopen.87042*

stressed or nonirrigated vines, the sugar concentration of the berries produced under the former conditions increases slower, but finally they can get the same concentration if they remain in the vine (**Figure 6**) [71].

**Figure 5.**

*Advances in Grape and Wine Biotechnology*

following spring's growth.

*in* cv. *Tempranillo. After [64].*

**Figure 4.**

*2.3.1 Effects of irrigation on total soluble solids*

water deficit has a cumulative effect, probably due to reduced starch and sucrose accumulation in the perennial organs [65–67]. This is important since the sugars accumulated in the trunk and roots are the first carbohydrates to be used during the

*Leaf area per vine at ripening (green bars) and winter pruning weight (blue line) from rainfed vines and three irrigation treatments applying 25, 50 and 100% of vine evapotranspiration (ETc) in averaged over four seasons* 

Total soluble solids (TSS) accumulate in the berry during phase III of berry growth. The increase in sugar content (°Brix) is coupled with a resumption in berry growth, accompanied by a sharp increase in berry weight (**Figure 5**). At the beginning of ripening, sugar accumulation occurs through leaf photosynthesis and through the mobilisation of reserves [68] although this mobilisation soon ceases. Sugar is transported from leaves to the berry via phloem in the form of sucrose. Once in the berry, it is changed into glucose and fructose, the ratio between them remaining close to 1:1 throughout ripening [2]. Since the TSS content is directly related to leaf photosynthetic activity [2, 69], sugar content can be used to indirectly evaluate the plant photosynthesis activity. At the end of ripening, photoassimilates also divert

to the fruit and to reserve tissues in the perennial parts of the plant [68].

differ depending on variety, cultivation practices and climate.

A linear relationship exists between berry size and TSS (**Figure 6**). Thus, berry size provides a meaningful, inexpensive means of estimating plant activity and tracking ripening. At the end of the ripening period, the increase in berry weight levels off, and the discharge of sugar into the berry ends. When the berries reach maximum TSS due to photosynthesis, ripening is finished. The final °Brix may

The amount of available water influences both the sugar accumulation rate and berry size. Studies have shown that, under water deficit conditions, °Brix increases faster than under high soil water conditions (**Figures 5** and **6**). This means that for the same berry weight, the °Brix reached in rainfed vines (or grown under water deficit conditions) is higher than those reached in well-irrigated vines [33, 71]. However, sugar accumulation expressed on a per-berry basis is higher for irrigated vines. Since irrigated vines produce higher yields than either moderately water

**2.3 Effects of vine water status on must and wine composition**

**80**

*Seasonal change in 100-berry weight in cv. Merlot in two shoot load treatments. Compact circles represent a shoot load of 12 shoots per metre of row; open circles represent minimal pruning conditions. Unpublished data.*

#### **Figure 6.**

*Change in the relationship between berry size and TSS under three irrigation regimens in cv. Cabernet sauvignon in Madrid (Spain). T1: rainfed (Y = 0.37x − 9.0R2 = 0.50\*), T2: irrigated 0.4·ETo (Y = 23.2Ln(x) − 85.12R2 = 0.68\*\*), T3: irrigated 0.2·ETo (Y = 0.40x − 15.82R2 = 0.71\*\*) [70].*

Berries increase in weight according to the availability of soil water. In trials involving different irrigation treatments, seasonal berry weight trends run in accordance with the supply of water [33, 72]. However, other authors report that berry sugar concentration may not differ between irrigation treatments since the smaller photosynthetic rate reached during ripening may be compensated for by a smaller berry weight [6, 71, 73]. Under moderate water stress, berry weight is reduced, but ripening quality in terms of sugar content is unaffected [9, 21, 74–76]. When water deficit is very mild, neither berry size nor sugar content is affected [77].

Although berry sugar concentration may not be affected by an increase in water deficit, other must components—such as anthocyanins [6]—may be. When water deficit has been long and intense, photosynthetic rates become low, and leaf abscission can occur at mid ripening, collapsing the ripening process [6, 69, 72]. Thus, final sugar content depends on water deficit intensity and deficit timing; several authors [8, 9, 59, 69, 70, 72, 78] have examined the thresholds between moderate deficit and severe water stress; on the whole, a midday stem water potential (Ψs) of −1.2/−1.3 MPa is required to maintain the yield and must quality within the required range. A midday Ψs of ≤1.4 MPa has clearly detrimental effects on photosynthesis, quality and yield. Some authors report that over optimal irrigation can have a detrimental effect on sugar content and lead to delayed ripening, increased acidity, reduced berry colour intensity and a smaller yield [35, 79–81], but in some of these experiments, however, midday Ψs was kept at above −0.9 MPa [80].

#### *2.3.2 Effects of irrigation on pH and titratable acidity*

Must titratable acidity and pH are important quality variables in winemaking. They both affect wine perception in the mouth (including smoothness, freshness and stringency). pH also influences the colour of the anthocyanins (red-blue at pH 3.0, orange near pH 4.0 and transparent at around pH 7.0), conditions microbial stability and when low acts as a shield against oxidation in musts and wines.

Organic acids accumulate in the berries during pre-*veraison*, increasing in concentration from fruit set to the end of phase II of berry growth [2]. At the end of this phase, the berries contain many different acids, but tartaric and malic acids together account for 70–90% of the total acid content.

During ripening, the berry acid content decreases by (1) dilution as sap flows inwards from the phloem, (2) by malate being used as a carbon source in respiration and (3) by gluconeogenesis in the berry, although this is responsible for only a small amount. Citric acid transforms into malic acid which might then follow any of its degradation routes. During ripening, the total acid content of the berry decreases, and the pH increases (**Figure 7**). At the end of ripening, the berry acid content and pH depend on the balance between the acid content at pre-*veraison*, leaf photosynthetic activity during pre- and post-*veraison*, the vine microclimate during pre- and post-*veraison*, final berry size and the berry cation (Ca2+ and K+ ) content, which transforms free acids into their corresponding salts. Variety and rootstock influence cation uptake, thus affecting the final pH too.

In trials, the effects of irrigation on total acidity and pH have been inconsistent. Irrigation has been reported to increase, reduce or not affect either variable. Esteban et al. [71] in a trial comparing nonirrigated and irrigated vines of cv. Tempranillo grafted onto 110 Richter rootstocks found that the grape must of the irrigated vines had lower pH and higher titratable acidity. In contrast, after a 5-year study of different irrigation regimens on cv. Cabernet Sauvignon/SO4, Junquera et al. [6] reported a positive relationship between water availability and total acidity but indicated that must pH was unaffected by irrigation. Differently again, after a 5-year of study involving cv. Tempranillo/161-49C, Intrigliolo and Castel [33] concluded that the

**83**

*Effects of Vine Water Status on Yield Components, Vegetative Response and Must and Wine…*

only detrimental effect of irrigation was an increase in pH compared to no irrigation, with total acidity increasing. In another trial involving cv. Tempranillo in pots, [72] titratable acidity increased with increasing water stress regardless of the stage at which water stress was induced. Working in a very warm region with the white cultivar Doña Blanca, Uriarte et al. [73] reported higher tartaric acid and lower malic contents in the must of water deficit vines, regardless when water deficit was induced. However, after a 3-year trial on cv. Monastrell/1103 Pa [81], neither titratable acidity nor the malic or tartaric acid contents were altered by any irrigation

*Seasonal change in titratable acidity (compact lines) and pH (dashed lines) in cv. Graciano/41B under* 

*optimum water availability (compact circles) and water deficit conditions (empty circles).*

irrigation treatment, but these differences were negligible from an oenological point of view; adding to the confusion, the tartaric and malic acid contents were inconsis-

These apparently very contradictory results do have some explanation, however, when examined taking into account vine physiology and factors that regulate the synthesis, accumulation and breakdown of these components [24, 69, 81, 82]: when water deficit is imposed from early in the season up to *veraison*, it negatively affects vigour, berry size and photosynthetic rate. If the photosynthetic rate is low, the acid and phenol contents accumulated in the berry during phase I are reduced [71, 83, 84]. On the contrary, optimal vine water status during this phase enhances photosynthetic

Esteban et al. [71] and other works obtained a tight positive, linear relation-

in grape must. Potassium is meanly accumulated in berry

activity, vigour and the acid and phenol content in the berries.

The results of other authors have further compounded the problem. For instance, neither Acevedo-Opazo [59], who ran a 3-year trial on cv. Cabernet Sauvignon in Chile, nor Munitz et al. [32], in their 4-year trial in Israel involving cv. Merlot, could found any differences in total acidity or pH between irrigation treatments. However, in a trial involving cv. Tempranillo/110R under a wide range of irrigation doses between budbreak and *veraison* and between *veraison* and harvest, Santesteban et al. [24] obtained higher titratable acidity values in the higher irrigation treatments before *veraison* (average predawn leaf water potential ~ −0.35 MPa). Regarding organic acid results, differences were significant 2 years out of 4 for the tartaric and malic acid contents which make us to state that irrigation effects on

to be significantly reduced in the highest

*DOI: http://dx.doi.org/10.5772/intechopen.87042*

treatment. They did indicate pH and K+

tent from 1 year to the next.

**Figure 7.**

must acidity are still inconclusive.

ship between pH and K+

*Effects of Vine Water Status on Yield Components, Vegetative Response and Must and Wine… DOI: http://dx.doi.org/10.5772/intechopen.87042*

#### **Figure 7.**

*Advances in Grape and Wine Biotechnology*

Berries increase in weight according to the availability of soil water. In trials involving different irrigation treatments, seasonal berry weight trends run in accordance with the supply of water [33, 72]. However, other authors report that berry sugar concentration may not differ between irrigation treatments since the smaller photosynthetic rate reached during ripening may be compensated for by a smaller berry weight [6, 71, 73]. Under moderate water stress, berry weight is reduced, but ripening quality in terms of sugar content is unaffected [9, 21, 74–76]. When water

Although berry sugar concentration may not be affected by an increase in water deficit, other must components—such as anthocyanins [6]—may be. When water deficit has been long and intense, photosynthetic rates become low, and leaf abscission can occur at mid ripening, collapsing the ripening process [6, 69, 72]. Thus, final sugar content depends on water deficit intensity and deficit timing; several authors [8, 9, 59, 69, 70, 72, 78] have examined the thresholds between moderate deficit and severe water stress; on the whole, a midday stem water potential (Ψs) of −1.2/−1.3 MPa is required to maintain the yield and must quality within the required range. A midday Ψs of ≤1.4 MPa has clearly detrimental effects on photosynthesis, quality and yield. Some authors report that over optimal irrigation can have a detrimental effect on sugar content and lead to delayed ripening, increased acidity, reduced berry colour intensity and a smaller yield [35, 79–81], but in some of these experiments, however, midday Ψs was kept at above −0.9 MPa [80].

Must titratable acidity and pH are important quality variables in winemaking. They both affect wine perception in the mouth (including smoothness, freshness and stringency). pH also influences the colour of the anthocyanins (red-blue at pH 3.0, orange near pH 4.0 and transparent at around pH 7.0), conditions microbial

During ripening, the berry acid content decreases by (1) dilution as sap flows inwards from the phloem, (2) by malate being used as a carbon source in respiration and (3) by gluconeogenesis in the berry, although this is responsible for only a small amount. Citric acid transforms into malic acid which might then follow any of its degradation routes. During ripening, the total acid content of the berry decreases, and the pH increases (**Figure 7**). At the end of ripening, the berry acid content and pH depend on the balance between the acid content at pre-*veraison*, leaf photosynthetic activity during pre- and post-*veraison*, the vine microclimate during pre- and

transforms free acids into their corresponding salts. Variety and rootstock influence

In trials, the effects of irrigation on total acidity and pH have been inconsistent. Irrigation has been reported to increase, reduce or not affect either variable. Esteban et al. [71] in a trial comparing nonirrigated and irrigated vines of cv. Tempranillo grafted onto 110 Richter rootstocks found that the grape must of the irrigated vines had lower pH and higher titratable acidity. In contrast, after a 5-year study of different irrigation regimens on cv. Cabernet Sauvignon/SO4, Junquera et al. [6] reported a positive relationship between water availability and total acidity but indicated that must pH was unaffected by irrigation. Differently again, after a 5-year of study involving cv. Tempranillo/161-49C, Intrigliolo and Castel [33] concluded that the

) content, which

stability and when low acts as a shield against oxidation in musts and wines. Organic acids accumulate in the berries during pre-*veraison*, increasing in concentration from fruit set to the end of phase II of berry growth [2]. At the end of this phase, the berries contain many different acids, but tartaric and malic acids

deficit is very mild, neither berry size nor sugar content is affected [77].

*2.3.2 Effects of irrigation on pH and titratable acidity*

together account for 70–90% of the total acid content.

post-*veraison*, final berry size and the berry cation (Ca2+ and K+

cation uptake, thus affecting the final pH too.

**82**

*Seasonal change in titratable acidity (compact lines) and pH (dashed lines) in cv. Graciano/41B under optimum water availability (compact circles) and water deficit conditions (empty circles).*

only detrimental effect of irrigation was an increase in pH compared to no irrigation, with total acidity increasing. In another trial involving cv. Tempranillo in pots, [72] titratable acidity increased with increasing water stress regardless of the stage at which water stress was induced. Working in a very warm region with the white cultivar Doña Blanca, Uriarte et al. [73] reported higher tartaric acid and lower malic contents in the must of water deficit vines, regardless when water deficit was induced. However, after a 3-year trial on cv. Monastrell/1103 Pa [81], neither titratable acidity nor the malic or tartaric acid contents were altered by any irrigation treatment. They did indicate pH and K+ to be significantly reduced in the highest irrigation treatment, but these differences were negligible from an oenological point of view; adding to the confusion, the tartaric and malic acid contents were inconsistent from 1 year to the next.

The results of other authors have further compounded the problem. For instance, neither Acevedo-Opazo [59], who ran a 3-year trial on cv. Cabernet Sauvignon in Chile, nor Munitz et al. [32], in their 4-year trial in Israel involving cv. Merlot, could found any differences in total acidity or pH between irrigation treatments. However, in a trial involving cv. Tempranillo/110R under a wide range of irrigation doses between budbreak and *veraison* and between *veraison* and harvest, Santesteban et al. [24] obtained higher titratable acidity values in the higher irrigation treatments before *veraison* (average predawn leaf water potential ~ −0.35 MPa). Regarding organic acid results, differences were significant 2 years out of 4 for the tartaric and malic acid contents which make us to state that irrigation effects on must acidity are still inconclusive.

These apparently very contradictory results do have some explanation, however, when examined taking into account vine physiology and factors that regulate the synthesis, accumulation and breakdown of these components [24, 69, 81, 82]: when water deficit is imposed from early in the season up to *veraison*, it negatively affects vigour, berry size and photosynthetic rate. If the photosynthetic rate is low, the acid and phenol contents accumulated in the berry during phase I are reduced [71, 83, 84]. On the contrary, optimal vine water status during this phase enhances photosynthetic activity, vigour and the acid and phenol content in the berries.

Esteban et al. [71] and other works obtained a tight positive, linear relationship between pH and K+ in grape must. Potassium is meanly accumulated in berry during maturation [85]; grapevines suffering water deficit during maturation have lower berry potassium concentration due to reduced mobility in soil and impaired root uptake [85]. This could explain the reduced pH in lower irrigated vines with respect to irrigated ones resulted in some trials [33]. Therefore, final pH and titratable acidity will depend on the timing and intensity of vine water deficit.

The effect of water deficit on must composition during ripening depends on the plant's previous water status. Mild water stress (midday Ψstem = −1.2/−1.3 MPa) after no previous water stress favours an optimal photosynthetic rate and sugar accumulation by the berries while avoiding excess berry growth. Thus, acids and phenols are not diluted and reach an optimal concentration at the end of ripening. Severe water deficit after *veraison* slows sugar accumulation severely and can collapse ripening. At this point, water stress favours leaf abscission, and the berries remain unripe with a high acid content, with a low sugar content and with an unripe colour and immature seeds. Early leaf fall renders the clusters more exposed to direct sunlight, affecting the breakdown of malate and the synthesis of anthocyanins. Either overirrigation or excess of available soil water after *veraison* may cause the berry acids to be diluted due to excess berry growth [16]. If there is a high soil water content, laterals develop and compete with the berries for sugars from leaf photosynthesis. Ripening is then delayed, something that could be sought more often in warm growing areas.

#### *2.3.3 Effects of vine irrigation on berry phenolic maturity and aroma compounds*

Volatile and phenolic compounds are grapevine secondary metabolites critical to grape quality and wine sensory attributes. Viticultural practices can influence the concentration of these compounds and their precursors in grapes via plant stress responses. Deficit irrigation (moderate water restriction), for example, is an important vineyard management strategy used to alter grape composition and therefore improve the final organoleptic quality of wine [85]. Water deficit in the vineyard reduces vegetative growth, alters the canopy microclimate and increases the amount of intercepted light in the cluster zone [9, 33, 86]. This renders the fruit more susceptible to heat stress, especially when there are high levels of ambient solar radiation. However, increased exposure of the fruit to sunlight has been associated with improvements in must and wine quality [87]. Indeed, several authors have reported it to be associated with increases in the volatile compound contents of grapes and wines, especially monoterpenes and carotenoids [88, 89]. Light and temperature also influence norisoprenoid concentrations, which correlate directly with the concentrations of carotenoids in grapes under moderate water stress [90, 91].

Both light intensity and temperature also affect phenolic compound composition and berry colour. Sunlight favours the accumulation of polyphenols in the berries, mainly anthocyanins [92, 93], but increased temperatures from excessive exposure to sunlight may lead to reduced berry colour, especially in warm-climate regions [94–96].

Berry size is widely acknowledged to affect berry quality. Vine water deficits generally lead to smaller berries being produced and changes in fruit and wine composition [74]. Depending on the moment of induction of water stress and its severity, the proportion of skin surface area to mesocarp volume changes [74, 97] as does the rate of biosynthesis and degradation of volatile [98] and phenolic compounds [97]. Several authors have reported the effect of vine water status on grape and wine volatile compounds [98–106], while Chapman et al. [99] showed that water deficit influences berry composition and improves wine sensorial quality, increasing fruity aromas and reducing vegetation aromas.

Bindon et al. [101] report that deficit irrigation increases the concentration of some C13-norisoprenoids, such as β-damascenone and β-ionone, in cv. Cabernet Sauvignon berries at harvest. Other studies also report a positive effect of deficit irrigation on

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*Effects of Vine Water Status on Yield Components, Vegetative Response and Must and Wine…*

grape and wine volatile compounds in cv. Cabernet Sauvignon berries [100, 105]. Water deficit also affects cv. Merlot grape maturity and composition. Deficit irrigation reduces the concentration of negative compounds and increases the concentration of positive compounds [102]. Certainly, Qian et al. [98] observed that cv. Merlot wine produced from deficit-irrigated vines has increased vitispirane, β-damascenone, guaiacol, 4-methylguaiacol, 4-ethylguaiacol and 4-vinylguaiacol concentrations compared to wines produced from well-watered vines. Deficit irrigation had no effect on the concentrations of other measured volatile compounds such as esters and terpenes. Similarly, Talaverano et al. [103] suggest that low water supply has a negative effect on the aromatic potential (mainly related to ethyl esters) of wines at a similar ripening stage. However, this effect could be countered by harvesting at a later date. Recent work reported by Vilanova et al. [105] shows that volatile composition in cv. Verdejo wines is modified by the water regimen, with concentrations increasing under

In a study examining the effect of irrigation on the sensory profile of wines from Galicia, those made with grapes of the white cultivars Albariño and Godello were judged to be better when the vines were rainfed rather than irrigated. Wines made from cv. Treixadura grapes, however, were judged better when the vines were irrigated [107]. Balint and Reynolds [108] studied the effect of different irrigation strategies on cv. Cabernet Sauvignon aroma descriptors and reported regulated deficit irrigation (RDI) to improve wine quality over both full irrigation and no irrigation treatments. The 25-RDI (25% ETc) treatment especially returned higher scores for most of the positive sensory characteristics of cv. Cabernet wines. The former authors reported that soil and plant water status could be used to predict the flavour profile of these wines, reflecting the relationship of these variables with sensory descriptors. It was concluded that 100% water replacement was not recommendable at any phenological stage. However, 50 and 25% water replacement had

overall positive effects on fruit composition and wine varietal typicity.

Water deficit can enhance the accumulation of anthocyanins by stimulating anthocyanin hydroxylation [4, 97]. Castellarin et al. [109] showed that water deficits accelerate anthocyanin accumulation and increase the expression of many genes responsible for the biosynthesis of anthocyanins. Moreover, the concentrations of different individual phenolic compounds are reported to change in response to plant water status, with those of flavonol and proanthocyanidin less affected than those of anthocyanins [97]. Ojeda et al. [110] report that severe water deficit before *veraison* reduces cv. Syrah anthocyanin synthesis. Similar results were reported by Romero et al. [69], with severe water stress associated with total grape phenolic compound concentration in cv. Monastrell grapes. However, Casassa et al. [111] recently reported that early and full deficit irrigation applied at pre-*veraison* produced cv. Cabernet Sauvignon grapes and wines with higher concentrations of phenolic compounds. In general, moderate water stress increases the concentrations of these compounds in red grapes, improving berry quality. However, when a certain threshold of water stress is surpassed, these positive effects are reported to disappear [69]. Similarly, Delgado et al. [112] report that the use of less water can increase the chemical and sensorial quality of wine; this is of some significance in a climate change context in which water supplies may decline. Niculea et al. [113] report phenolic compound accumulation and composition responses to sustained deficit irrigation during berry growth and ripening to be variety-dependent. Finally, Herrera et al. [114] suggest that the interaction between water availability and weather conditions plays a crucial role in modulating berry composition. A meta-analysis performed by Mirás-Avalos and Intrigliolo [115], using published data for red and white varieties, concludes that cultivar, the timing of water restrictions and rootstock type have a great influence on must and wine composition. The

*DOI: http://dx.doi.org/10.5772/intechopen.87042*

the most severe deficit irrigation regime.

#### *Effects of Vine Water Status on Yield Components, Vegetative Response and Must and Wine… DOI: http://dx.doi.org/10.5772/intechopen.87042*

grape and wine volatile compounds in cv. Cabernet Sauvignon berries [100, 105]. Water deficit also affects cv. Merlot grape maturity and composition. Deficit irrigation reduces the concentration of negative compounds and increases the concentration of positive compounds [102]. Certainly, Qian et al. [98] observed that cv. Merlot wine produced from deficit-irrigated vines has increased vitispirane, β-damascenone, guaiacol, 4-methylguaiacol, 4-ethylguaiacol and 4-vinylguaiacol concentrations compared to wines produced from well-watered vines. Deficit irrigation had no effect on the concentrations of other measured volatile compounds such as esters and terpenes. Similarly, Talaverano et al. [103] suggest that low water supply has a negative effect on the aromatic potential (mainly related to ethyl esters) of wines at a similar ripening stage. However, this effect could be countered by harvesting at a later date. Recent work reported by Vilanova et al. [105] shows that volatile composition in cv. Verdejo wines is modified by the water regimen, with concentrations increasing under the most severe deficit irrigation regime.

In a study examining the effect of irrigation on the sensory profile of wines from Galicia, those made with grapes of the white cultivars Albariño and Godello were judged to be better when the vines were rainfed rather than irrigated. Wines made from cv. Treixadura grapes, however, were judged better when the vines were irrigated [107]. Balint and Reynolds [108] studied the effect of different irrigation strategies on cv. Cabernet Sauvignon aroma descriptors and reported regulated deficit irrigation (RDI) to improve wine quality over both full irrigation and no irrigation treatments. The 25-RDI (25% ETc) treatment especially returned higher scores for most of the positive sensory characteristics of cv. Cabernet wines. The former authors reported that soil and plant water status could be used to predict the flavour profile of these wines, reflecting the relationship of these variables with sensory descriptors. It was concluded that 100% water replacement was not recommendable at any phenological stage. However, 50 and 25% water replacement had overall positive effects on fruit composition and wine varietal typicity.

Water deficit can enhance the accumulation of anthocyanins by stimulating anthocyanin hydroxylation [4, 97]. Castellarin et al. [109] showed that water deficits accelerate anthocyanin accumulation and increase the expression of many genes responsible for the biosynthesis of anthocyanins. Moreover, the concentrations of different individual phenolic compounds are reported to change in response to plant water status, with those of flavonol and proanthocyanidin less affected than those of anthocyanins [97]. Ojeda et al. [110] report that severe water deficit before *veraison* reduces cv. Syrah anthocyanin synthesis. Similar results were reported by Romero et al. [69], with severe water stress associated with total grape phenolic compound concentration in cv. Monastrell grapes. However, Casassa et al. [111] recently reported that early and full deficit irrigation applied at pre-*veraison* produced cv. Cabernet Sauvignon grapes and wines with higher concentrations of phenolic compounds. In general, moderate water stress increases the concentrations of these compounds in red grapes, improving berry quality. However, when a certain threshold of water stress is surpassed, these positive effects are reported to disappear [69]. Similarly, Delgado et al. [112] report that the use of less water can increase the chemical and sensorial quality of wine; this is of some significance in a climate change context in which water supplies may decline. Niculea et al. [113] report phenolic compound accumulation and composition responses to sustained deficit irrigation during berry growth and ripening to be variety-dependent.

Finally, Herrera et al. [114] suggest that the interaction between water availability and weather conditions plays a crucial role in modulating berry composition. A meta-analysis performed by Mirás-Avalos and Intrigliolo [115], using published data for red and white varieties, concludes that cultivar, the timing of water restrictions and rootstock type have a great influence on must and wine composition. The

*Advances in Grape and Wine Biotechnology*

during maturation [85]; grapevines suffering water deficit during maturation have lower berry potassium concentration due to reduced mobility in soil and impaired root uptake [85]. This could explain the reduced pH in lower irrigated vines with respect to irrigated ones resulted in some trials [33]. Therefore, final pH and titrat-

The effect of water deficit on must composition during ripening depends on the plant's previous water status. Mild water stress (midday Ψstem = −1.2/−1.3 MPa) after no previous water stress favours an optimal photosynthetic rate and sugar accumulation by the berries while avoiding excess berry growth. Thus, acids and phenols are not diluted and reach an optimal concentration at the end of ripening. Severe water deficit after *veraison* slows sugar accumulation severely and can collapse ripening. At this point, water stress favours leaf abscission, and the berries remain unripe with a high acid content, with a low sugar content and with an unripe colour and immature seeds. Early leaf fall renders the clusters more exposed to direct sunlight, affecting the breakdown of malate and the synthesis of anthocyanins. Either overirrigation or excess of available soil water after *veraison* may cause the berry acids to be diluted due to excess berry growth [16]. If there is a high soil water content, laterals develop and compete with the berries for sugars from leaf photosynthesis. Ripening is then delayed, something that could be sought more often in warm growing areas.

able acidity will depend on the timing and intensity of vine water deficit.

*2.3.3 Effects of vine irrigation on berry phenolic maturity and aroma compounds*

tions of carotenoids in grapes under moderate water stress [90, 91].

increasing fruity aromas and reducing vegetation aromas.

Volatile and phenolic compounds are grapevine secondary metabolites critical to grape quality and wine sensory attributes. Viticultural practices can influence the concentration of these compounds and their precursors in grapes via plant stress responses. Deficit irrigation (moderate water restriction), for example, is an important vineyard management strategy used to alter grape composition and therefore improve the final organoleptic quality of wine [85]. Water deficit in the vineyard reduces vegetative growth, alters the canopy microclimate and increases the amount of intercepted light in the cluster zone [9, 33, 86]. This renders the fruit more susceptible to heat stress, especially when there are high levels of ambient solar radiation. However, increased exposure of the fruit to sunlight has been associated with improvements in must and wine quality [87]. Indeed, several authors have reported it to be associated with increases in the volatile compound contents of grapes and wines, especially monoterpenes and carotenoids [88, 89]. Light and temperature also influence norisoprenoid concentrations, which correlate directly with the concentra-

Both light intensity and temperature also affect phenolic compound composition and berry colour. Sunlight favours the accumulation of polyphenols in the berries, mainly anthocyanins [92, 93], but increased temperatures from excessive exposure to sunlight may lead to reduced berry colour, especially in warm-climate regions [94–96]. Berry size is widely acknowledged to affect berry quality. Vine water deficits generally lead to smaller berries being produced and changes in fruit and wine composition [74]. Depending on the moment of induction of water stress and its severity, the proportion of skin surface area to mesocarp volume changes [74, 97] as does the rate of biosynthesis and degradation of volatile [98] and phenolic compounds [97]. Several authors have reported the effect of vine water status on grape and wine volatile compounds [98–106], while Chapman et al. [99] showed that water deficit influences berry composition and improves wine sensorial quality,

Bindon et al. [101] report that deficit irrigation increases the concentration of some C13-norisoprenoids, such as β-damascenone and β-ionone, in cv. Cabernet Sauvignon berries at harvest. Other studies also report a positive effect of deficit irrigation on

**84**

effects of other factors, such as climate, the leaf surface/yield ratio and training systems, need to be examined in future research.

The effect of RDI on grape volatile and phenolic compounds remains incompletely understood, and further investigations are required to determine what compounds are influenced by irrigation. The timing, severity, duration of water stress, seasonal variations, the type of cultivar and the interaction of *genotype x environment* can all influence the response of vines to water stress, probably explaining the discrepancies seen in the results of different studies.
