**2. Effects of plant water status on vine response**

#### **2.1 Effects of vine water status on yield components**

Different components are taken into account when calculating the yield of a vineyard. The yield per hectare can be expressed as follows:

$$\text{Yield} = \frac{\text{N\text{\textdegree}}}{\text{ha}} \cdot \frac{\text{N\text{\textdegree}}}{\text{vine}} \cdot \frac{\text{N\text{\textdegree}}}{\text{bud}} \cdot \frac{\text{N\text{\textdegree}}}{\text{bud}} \cdot \frac{\text{N\text{\textdegree}}}{\text{shoot}} \cdot \frac{\text{N\text{\textdegree}}}{\text{cluster}} \cdot \frac{\text{N\text{\textdegree}}}{\text{cluster}} \cdot \text{bertry weight} \quad (1)$$

**75**

**Figure 1.**

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

nutrients from the reserve structures is reduced [1]. Once the number of potentially productive shoots is defined, the yield of a vineyard depends on a set of internal and external factors, and the interactions among them, all of which have an impact on the processes of floral induction and differentiation and the growth of the berries. These factors include the genotype of the vine (variety and rootstock), environ-

*Relationship between crop yield and water supply (rainfall + irrigation) from budbreak to harvest in a cv. Cabernet sauvignon vineyard in Madrid, Spain. Data correspond to five different irrigation treatments* 

Water deficit is one of the main environmental factors limiting vegetative growth and berry yield [3, 4] (reproductive development is less sensitive to water shortages than vegetative growth [5]). The water status of a vineyard depends on the availability of water (soil water, rainfall and irrigation), atmospheric conditions (relative humidity, vapour pressure deficit, temperature, etc.) and leaf area as well

Some studies have reported a direct relationship between the amount of water available during the growth cycle (rainfall + irrigation) and yield (**Figure 1**) [6, 7]. However, this relationship is not immediately obvious when data from different studies are brought together in the search for correlations. This is largely the consequence of differences in environmental conditions (soil and climate) and vineyard characteristics (genotype, training system, etc.), which generate differences in

analysis conducted by Medrano et al. [8] clearly shows a positive linear relationship between yield and water use efficiency, even when an increase in the latter can only be achieved by reducing the total amount of water used—which generally involves a certain reduction in yield. Indeed, several studies have concluded that irrigation doses equivalent to 60–80% of crop evapotranspiration (ETc) are sufficient to maximise yield [9–11]. Irrigation doses exceeding 100% ETc might lower yield via reductions in fertility, and even in berry weight, perhaps due to competition

Reproductive growth correlates with water availability, with this relationship dependent on the development stage of the vine. Generally, water deficit reduces yield,

water applied) [8]. However, the meta-

mental conditions (climate and soil) and cultivation practices [2].

*applied during 2002–2006 (adapted from Junquera et al. [6]).*

as the ability of the vine to absorb and transport water to its organs.

water use efficiency (kg fresh fruit/m3

between berry and vegetative growth [10].

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

The vine spacing, training system and pruning level determine the number of potentially productive buds. In most viticultural regions, budburst follows its normal course since soil water is usually available. However, a strong water deficit at the beginning of the season negatively affects budburst since the mobilisation of *Effects of Vine Water Status on Yield Components, Vegetative Response and Must and Wine… DOI: http://dx.doi.org/10.5772/intechopen.87042*

**Figure 1.**

*Advances in Grape and Wine Biotechnology*

introducing irrigation.

and the consequences of global warming are felt.

**2. Effects of plant water status on vine response**

**2.1 Effects of vine water status on yield components**

ha · \_\_\_\_\_\_ N°buds

vineyard. The yield per hectare can be expressed as follows:

vine · \_\_\_\_\_\_\_\_ N°shoots

optimal-severe available water took place.

Yield = \_\_\_\_\_\_\_

N°vines

Along history, growers have been forced to choose those cultivars best adapted to the local availability of water, seasonal temperatures, the dry periods they must face, etc., increasing experience allowing the most to be made of each situation. Different training systems and cultivation practices have also been developed, striking a balance between plant, vineyard management and the environment and giving rise to different viticultural landscapes, some now recognized as part of the world heritage. This balance, however, can be altered when priorities change, perhaps driven by the desire to produce more, or because of a change in market conditions. Thus, an area might need to increase yields or open up new areas of sustainable production. Areas naturally suited to raising white wine grape varieties might suddenly need to shift to red, or the variety habitually grown may need to be changed due to customer demand. Under certain circumstances, newly imposed conditions can only be met sustainably by modifying the vineyard agrosystem, perhaps by introducing a different kind of trellising or canopy management or by

For a long time, the drought tolerance of grapevines meant irrigation was not contemplated as a viticultural practice. Indeed, it took hard work to overcome the prejudice that grapevines are not well suited to it. By and large, vineyards in growing areas brought into production in the last 50 years have been irrigated. In some traditional areas, however, irrigation was banned until some decades ago. Irrigation results obtained from vineyards under regional regulations (geographical indications), with limitations either to yield or bud load, for example, may complicate the discussions of irrigation as it often happens that irrigated vines cannot express the most of them when we are limiting their optimal performance under those new conditions and when they are harvested at the same date. This turned out that part of the industry felt that the best wines were produced under situations of severe water stress. The aim of irrigating wine grapes is not always to produce higher yields but to ensure the quality required for different products. For example, some grapes are grown with the intention of producing young wines, others are raised to make wines for ageing and yet others for making spirits, etc.; as a result, they require different irrigation regimens and different optimal yields and different harvest time. In recent times, attitudes are changing as irrigation studies have increased and irrigation management becomes ever more technically friendly and controllable,

In the following paragraphs, a review of the effects of water status on yield, vine growth and must and wine composition is exposed, and results are explained taken into account the phenological stage and the berry growth stage at which excess-

Different components are taken into account when calculating the yield of a

The vine spacing, training system and pruning level determine the number of potentially productive buds. In most viticultural regions, budburst follows its normal course since soil water is usually available. However, a strong water deficit at the beginning of the season negatively affects budburst since the mobilisation of

bud · \_\_\_\_\_\_\_\_\_ N°clusters

shoot · \_\_\_\_\_\_\_\_ N°berries

cluster · berry weight (1)

**74**

*Relationship between crop yield and water supply (rainfall + irrigation) from budbreak to harvest in a cv. Cabernet sauvignon vineyard in Madrid, Spain. Data correspond to five different irrigation treatments applied during 2002–2006 (adapted from Junquera et al. [6]).*

nutrients from the reserve structures is reduced [1]. Once the number of potentially productive shoots is defined, the yield of a vineyard depends on a set of internal and external factors, and the interactions among them, all of which have an impact on the processes of floral induction and differentiation and the growth of the berries. These factors include the genotype of the vine (variety and rootstock), environmental conditions (climate and soil) and cultivation practices [2].

Water deficit is one of the main environmental factors limiting vegetative growth and berry yield [3, 4] (reproductive development is less sensitive to water shortages than vegetative growth [5]). The water status of a vineyard depends on the availability of water (soil water, rainfall and irrigation), atmospheric conditions (relative humidity, vapour pressure deficit, temperature, etc.) and leaf area as well as the ability of the vine to absorb and transport water to its organs.

Some studies have reported a direct relationship between the amount of water available during the growth cycle (rainfall + irrigation) and yield (**Figure 1**) [6, 7]. However, this relationship is not immediately obvious when data from different studies are brought together in the search for correlations. This is largely the consequence of differences in environmental conditions (soil and climate) and vineyard characteristics (genotype, training system, etc.), which generate differences in water use efficiency (kg fresh fruit/m3 water applied) [8]. However, the metaanalysis conducted by Medrano et al. [8] clearly shows a positive linear relationship between yield and water use efficiency, even when an increase in the latter can only be achieved by reducing the total amount of water used—which generally involves a certain reduction in yield. Indeed, several studies have concluded that irrigation doses equivalent to 60–80% of crop evapotranspiration (ETc) are sufficient to maximise yield [9–11]. Irrigation doses exceeding 100% ETc might lower yield via reductions in fertility, and even in berry weight, perhaps due to competition between berry and vegetative growth [10].

Reproductive growth correlates with water availability, with this relationship dependent on the development stage of the vine. Generally, water deficit reduces yield, particularly when shortages occur early in the season [12]. However, the complexity and duration of the reproductive cycle of the vine make a more detailed analysis necessary. The reproductive cycle of the vine is completed after a 2-year period: the buds formed in the first season develop and give rise to fruiting shoots in the following season. This process includes numerous phenomena: induction and floral differentiation, flowering, pollination, fertilisation, fruit setting and berry growth [13]. Thus, there is a long period of time over which the yield is liable to alterations due to environmental conditions and/or vineyard management practices.

Intense and persistent water deficits usually reduce bud fertility via falls in the number and size of inflorescences [14]. Induction is particularly sensitive to water stress, with shortages during flowering normally leading to important reductions in bud fertility [15]. Vasconcelos et al. [1] reviewed the different means by which water status can affect floral induction and differentiation, and therefore bud fertility, reporting it to be influenced (1) directly, via the amount of water available to processes determining cell division and expansion, and (2) indirectly, via its effect on photosynthetic activity, nutrition, the microclimate of the renewal zone and hormonal balance. These authors also indicate that the many determining factors and possible interactions among them make it difficult to establish clear correlations between water status and bud fertility. Certainly, the potential for reduced fertility exists via excessive water availability leading to increased vigour and vegetative growth and therefore reduced light interception in the renewal zone [1, 16, 17]. This same excessive vigour and lack of illumination can, however, also favour primary bud necrosis and therefore a lack of primary bud growth at budbreak and reduced fertility [10, 18]. Fertility can thus be reduced by both limited and excessive water availability.

Shortly after budburst, reproductive growth is relatively unaffected by water deficit. In most viticultural regions, water deficit is not normally a problem during inflorescence development; the soil water content is generally sufficient throughout spring, supplied either by rain or irrigation. Moreover, at this point in the reproductive cycle, inflorescences are able to compete for photoassimilates against the vegetative structures of the shoots, with the production of carbohydrates by the former sufficient for self-supply. It is only later, during flowering, when vine requirements for photoassimilates exceed photosynthetic capacity and the sensitivity to water deficit increases [16]. Of course, there may be times when drought conditions occur even during early spring. Excessive water deficit at this time can cause the vine to loose whole inflorescences, reducing the eventual number of future clusters. This is particularly true when such drought conditions are combined with high temperatures and low vigour [13].

The reviews by McCarthy [19] and Keller [16] reveal the importance of vine water status during the flowering period. The male organs are more sensitive to this variable than the female organs; deficits near the time of flowering may limit ovary growth, leading to smaller berries, but the effects on pollen formation, germination and pollen tube growth are even more severe. Water deficit, like other stressors, can limit sugar uptake and starch accumulation in developing pollen grains, causing sterility and compromising the course of fertilisation and fruit set, even leading to the loss of whole inflorescences [2]. Severe water stress during fruit set can reduce the success of this stage via reductions in the photosynthetic rate and carbohydrate availability [17].

Once fruit set has taken place, and the final number of berries in the vineyard is determined, the last yield component to play a role in the yield is berry weight. Berry development follows a double sigmoid curve [20] that can be divided into three stages. In Stage I (the beginning of the green phase of berry development), berry growth is caused by cell division and enlargement. Stage II is the shortest stage; growth at this point is markedly reduced. At the end of Stage II, the berry colour starts

**77**

**Figure 2.**

*and after veraison. Unpublished data.*

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

to change, and metabolic processes that trigger ripening take place. This moment in the cycle is called veraison. In Stage III, the so-called ripening, berry growth is restarted due to cell enlargement. During Stage I, both multiplication and cell growth can be affected by water stress, although multiplication is less sensitive than cell enlargement. Water stress at this time alters the properties of the cell wall, irreversibly restricting the capacity for cell enlargement [21]. Later on in the cycle, only cell expansion is affected by water stress, limiting berry and seed growth. However the effect here is never as significant as in the earlier stages. Berries become increasingly resistant to stress from veraison onward. In fact, the reduction in yield due to water deficit is much more important when this occurs before veraison, as made clear by

*Change in berry weight for five different irrigation treatments applied during 2004 in a cv. Cabernet sauvignon vineyard in Madrid, Spain. Numbers for each treatment correspond to the %ETc applied by irrigation before* 

numerous studies on regulated deficit irrigation (**Figure 2**) [6, 12, 22–25].

(b) the berries become vascularly disconnected from the vine (Chardonnay).

In their review, Chaves et al. [4] indicate the effect on photosynthesis to be the main cause of water availability-induced reductions in berry growth after veraison. During ripening, the berries take up water mainly via the phloem; uptake from the xylem is very limited. Occasionally, berry weight losses are observed in late ripening, reducing the final yield (**Figure 3**). Recent studies have shown that, in addition to possible water losses by transpiration (which are less severe at this point than during Stage I), water return via the xylem may occur. This return is dependent on grape variety and is determined by the late-ripening integrity of the cell membranes and the hydraulic conductivity of the xylem [26, 27]. Different grape varieties show either isohydric or anisohydric water regulation behaviours at the leaf and root level; the idea of variety-dependent water regulation strategies at the berry level cannot, therefore, be ruled out [28]. Illand et al. [17] hypothesize weight loss taking place during late ripening whenever berries continue to be vascularly connected to the vine and there is a loss in cell viability (shrinkage in Syrah). This suggests that weight loss would not occur if (a) cell viability is preserved (Thompson Seedless) or

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

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

**Figure 2.**

*Advances in Grape and Wine Biotechnology*

particularly when shortages occur early in the season [12]. However, the complexity and duration of the reproductive cycle of the vine make a more detailed analysis necessary. The reproductive cycle of the vine is completed after a 2-year period: the buds formed in the first season develop and give rise to fruiting shoots in the following season. This process includes numerous phenomena: induction and floral differentiation, flowering, pollination, fertilisation, fruit setting and berry growth [13]. Thus, there is a long period of time over which the yield is liable to alterations due to environ-

Intense and persistent water deficits usually reduce bud fertility via falls in the number and size of inflorescences [14]. Induction is particularly sensitive to water stress, with shortages during flowering normally leading to important reductions in bud fertility [15]. Vasconcelos et al. [1] reviewed the different means by which water status can affect floral induction and differentiation, and therefore bud fertility, reporting it to be influenced (1) directly, via the amount of water available to processes determining cell division and expansion, and (2) indirectly, via its effect on photosynthetic activity, nutrition, the microclimate of the renewal zone and hormonal balance. These authors also indicate that the many determining factors and possible interactions among them make it difficult to establish clear correlations between water status and bud fertility. Certainly, the potential for reduced fertility exists via excessive water availability leading to increased vigour and vegetative growth and therefore reduced light interception in the renewal zone [1, 16, 17]. This same excessive vigour and lack of illumination can, however, also favour primary bud necrosis and therefore a lack of primary bud growth at budbreak and reduced fertility [10, 18]. Fertility can thus be reduced by both limited and excessive water availability. Shortly after budburst, reproductive growth is relatively unaffected by water deficit. In most viticultural regions, water deficit is not normally a problem during inflorescence development; the soil water content is generally sufficient throughout spring, supplied either by rain or irrigation. Moreover, at this point in the reproductive cycle, inflorescences are able to compete for photoassimilates against the vegetative structures of the shoots, with the production of carbohydrates by the former sufficient for self-supply. It is only later, during flowering, when vine requirements for photoassimilates exceed photosynthetic capacity and the sensitivity to water deficit increases [16]. Of course, there may be times when drought conditions occur even during early spring. Excessive water deficit at this time can cause the vine to loose whole inflorescences, reducing the eventual number of future clusters. This is particularly true when such drought conditions are combined with high tempera-

The reviews by McCarthy [19] and Keller [16] reveal the importance of vine water status during the flowering period. The male organs are more sensitive to this variable than the female organs; deficits near the time of flowering may limit ovary growth, leading to smaller berries, but the effects on pollen formation, germination and pollen tube growth are even more severe. Water deficit, like other stressors, can limit sugar uptake and starch accumulation in developing pollen grains, causing sterility and compromising the course of fertilisation and fruit set, even leading to the loss of whole inflorescences [2]. Severe water stress during fruit set can reduce the success of this stage via reductions in the photosynthetic rate and carbohydrate

Once fruit set has taken place, and the final number of berries in the vineyard is determined, the last yield component to play a role in the yield is berry weight. Berry development follows a double sigmoid curve [20] that can be divided into three stages. In Stage I (the beginning of the green phase of berry development), berry growth is caused by cell division and enlargement. Stage II is the shortest stage; growth at this point is markedly reduced. At the end of Stage II, the berry colour starts

mental conditions and/or vineyard management practices.

**76**

tures and low vigour [13].

availability [17].

*Change in berry weight for five different irrigation treatments applied during 2004 in a cv. Cabernet sauvignon vineyard in Madrid, Spain. Numbers for each treatment correspond to the %ETc applied by irrigation before and after veraison. Unpublished data.*

to change, and metabolic processes that trigger ripening take place. This moment in the cycle is called veraison. In Stage III, the so-called ripening, berry growth is restarted due to cell enlargement. During Stage I, both multiplication and cell growth can be affected by water stress, although multiplication is less sensitive than cell enlargement. Water stress at this time alters the properties of the cell wall, irreversibly restricting the capacity for cell enlargement [21]. Later on in the cycle, only cell expansion is affected by water stress, limiting berry and seed growth. However the effect here is never as significant as in the earlier stages. Berries become increasingly resistant to stress from veraison onward. In fact, the reduction in yield due to water deficit is much more important when this occurs before veraison, as made clear by numerous studies on regulated deficit irrigation (**Figure 2**) [6, 12, 22–25].

In their review, Chaves et al. [4] indicate the effect on photosynthesis to be the main cause of water availability-induced reductions in berry growth after veraison. During ripening, the berries take up water mainly via the phloem; uptake from the xylem is very limited. Occasionally, berry weight losses are observed in late ripening, reducing the final yield (**Figure 3**). Recent studies have shown that, in addition to possible water losses by transpiration (which are less severe at this point than during Stage I), water return via the xylem may occur. This return is dependent on grape variety and is determined by the late-ripening integrity of the cell membranes and the hydraulic conductivity of the xylem [26, 27]. Different grape varieties show either isohydric or anisohydric water regulation behaviours at the leaf and root level; the idea of variety-dependent water regulation strategies at the berry level cannot, therefore, be ruled out [28]. Illand et al. [17] hypothesize weight loss taking place during late ripening whenever berries continue to be vascularly connected to the vine and there is a loss in cell viability (shrinkage in Syrah). This suggests that weight loss would not occur if (a) cell viability is preserved (Thompson Seedless) or (b) the berries become vascularly disconnected from the vine (Chardonnay).

**Figure 3.** *Shrivelling and weight loss in cv. Graciano grapes during late ripening.*
