*4.3.2. Grapevines response to water stress*

Pérez-Sarmiento et al. [138] applying several RDI strategies to apricot have found improvements in some qualitative characteristics of the fruits, such as the level of soluble solids, sugar/ acid ratio, and fruit color, without negative effects in yield. Along with these characteristics, fruit firmness was also improved in a study conducted by Zhou et al. [135] when applying an SDI strategy with a light water stress. Therefore, from these studies, it can be concluded that the use of deficit irrigation in peach doesnot seem to induce negative effects in the fruit quality parameters referred above. Nevertheless, several authors refer the occurrence of double fruits or fruit cracking, if severe water stress is imposed. For example, Naor et al. [39] refer this occurrence for values of stem water potential lower than −2.0 MPa. This suggests that, in what concerns fruit quality, there is an identifiable limit to the application of deficit irrigation,

Most of the studies addressing water use efficiency (WUE) in peach under deficit irrigation report an increase in comparison to full irrigation practices, although with lower yields for

Grapevines (*Vitis vinifera* L.) develop over a number of periodic events, phenological stages, mentioned in the literature as budbreak, flowering and veraison [139]. Budbreak signals the beginning of the vine seasonal growth and physiological activity after a period of dormancy during the coldest months of the year but its starting date is neither influenced by winter temperature or precipitation [140, 141]. However, a recent report [142] mentions that waterstressed grapevines delay the onset of bud dormancy, reduce the cold exposure required for releasing buds from dormancy, and hasten budbreak. Flowering initiates the reproductive cycle and is followed by the fruit setting. At veraison, the ripening process is initiated when important must, and later wine, quality attributes develop. The time needed to reach berry maturity is related to temperature and precipitation and it is shortened as the temperature rises and precipitation decreases [141]. Grapevine phenology is strongly influenced by weather and climate [143] and the duration of each stage is largely determined by temperature [144]. Moreover, ambient temperature conditions the plant physiology, imparts the berry

The climates with best potentials for quality wines are those with mild and wet winters, warm springs, and hot and dry summers. These climatic characteristics are common for the so-called Mediterranean climate well-known for its dry summer, and grapevines are well adapted to water scarcity because of its extensive, deep roots, and mechanisms of drought resistance

The cultivation of grapevines, fruit in Europe is mainly used for winemaking, is a climatesensitive agricultural system and it expected a rise in average temperatures worldwide by 2050, some regions might be over the optimum range of temperature for the growing season [148]. Precipitation in many viticultural areas is expected to decrease substantially in the period between budbreaking and veraison [149] resulting in more intense water stress during

such as tight control of stomatal aperture [146] and osmotic adjustment [147].

as discussed in Section 4.

66 Irrigation in Agroecosystems

**4.3. Grapevines**

moderate or severe water stress [135].

*4.3.1. Vegetative growth and production cycle*

composition, and ultimately, the wine quality [145].

The wine grower has to manage irrigation for the benefit of yield and quality that maximizes the returns as the growers profits are a combination of both yield and quality, and a very low yield, no matter what quality might not be profitable [152].

It is well documented that irrigated grapevines increased significantly their yield per plant over rainfed plants. The increased yield is due to larger berries that diluted color, aroma, and soluble solids, and correspond to a lower quality of the must and hence the wine.

Imposing very high levels of water stress must be avoided because it results in declining vine capacity and productivity, eventually becoming economically unsustainable [153].

In viticultural regions where water stress can cause damages to the production objectives, DI strategy is a management tool that can ensure a balance between vegetative and reproductive development while maintaining yields and improving fruit composition [42] but the irrigation timing and amount must be adjusted to the local environment (*terroir*) and to wine typicity to avoid potential negative impacts [154]. Too small quantity of irrigation water can be an expensive procedure with no beneficial effect while too much water might induce an excessive vegetative growth, increase berry size, and reduce the concentration of important metabolites for quality wines [155].

Nevertheless, simultaneous events of high temperatures, drought and elevated evapotranspiration have detrimental effects on yield and berry composition as the plant carbon assimilation is much reduced due to lower photosynthetic activity compounded by loss of leaf area [156]. It is well documented that water stress decreases leaf stomatal conductance, leaf water potential, vegetative growth, leaf to fruit ratio, berry size and their fresh and dry weights, and yield [46, 141].

Water stress and temperature have a complex relationship. Higher temperatures can enhance both sugar accumulation and organic acid decay, but acidity is more affected than sugar levels, then, for the same sugar level, grapes grown under warmer conditions have lower acidity [157]. This decoupling has been reported for other metabolites, such as anthocyanins [141], proanthocyanidins [158], and aromas [159]. The decoupling of anthocyanins and sugars, in favor of anthocyanins, was observed in Cabernet Sauvignon under increasing water stress [160]. During the ripening period, if elevated temperature and drought occur simultaneously, the effects on the decoupling of anthocyanins and sugars can be felt only slightly due to the contrasting responses to these two factors, and in fact, restricted water supply during berry development can partially restore anthocyanin/sugar ratios disrupted by high temperature [161]. In "Red Tempranillo," elevated temperature and drought reduced total polyphenol index, malic acid and increased color density, but did not modify anthocyanin concentration [119].

Grapevines exhibit a vigorous vegetative growth between budbreak and veraison [162] and as consequence, the plant has its highest demand for water during this period. If there is an ample availability of soil water that might be supplemented with occasional rains, the plant grows a dense, shaded canopy at expense of reproductive berries with negative impacts on fruit and wine quality potential, foster pests and diseases, and the grower has to resort to expensive canopy management such as shoot and leaf thinning, hedging, and shoot repositioning to correct the canopy architecture and manipulate the plant yield [163]. Attending the effects of these contrasting conditions, a degree of water stress is considered beneficial for the production of quality grapes [164, 165].

growth, yield, and fruit metabolism [40]. Experiments with DI of "Tinta Roriz" (Tempranillo) carried in Alto Douro (Portugal) [152, 166] showed that RDI was effective to increase the yields and also induced higher concentration of organic acids in the musts but insufficient

Deficit Irrigation in Mediterranean Fruit Trees and Grapevines: Water Stress Indicators and Crop…

and the concentration of glucose and fructose decreased as the rate of irrigation increased, mainly if water was applied after veraison. Irrigation had no influence on pH, anthocyanidins and flavonols of the must when compared with rainfed grapevines, but the effect was negative upon the polyphenol index, the total anthocyanins, and the color intensity. The adverse effects of irrigation were mitigated when vines were deficit irrigated between flowering and veraison followed by no irrigation till harvest. Some of these results were corroborated by other authors [81, 174]. The experiment also showed that rainfed vines produced musts with attributes very desirable for high-end wines but the yield was too low (as little as 300 g per plant) to guarantee a satisfactory economic return. RDI can result in substantial improvements on fruit quality through decreasing yield and berry size [94] and has a positive effect over synthesis and concentration of phenolic compounds, soluble

The recommended irrigation strategy should be the one that maintains better tree water status throughout the season, depending on the soil water content at the beginning and the availability of water. These factors change between years, so deficit irrigation studies should be carried out for longer time than 2 or 3 years to produce a better knowledge of water stress

For the above reasons, and based on the successful use of RDI in fruit trees and grapevines reviewed herein, the adoption of RDI strategies in water-limited areas should be encouraged. So, it is of great importance to bear in mind that results depend mainly on cultivar, orchard characteristics, environmental conditions, and agronomic practices and to the large variability in rainfall, climate, and soil types between the various growing regions; thus caution must be taken when applying the findings reported by different authors to a particular

This work is supported by: European Investment Funds by FEDER/COMPETE/POCI— Operational Competitiveness and Internationalization Programme, under Project POCI-01-0145- FEDER-006958 and National Funds by FCT—Portuguese Foundation for Science and Technology, under the project UID/AGR/04033/2013" and by fellowship (FCT/SFRH/BD/18441/2004) awarded to Fernandes-Silva, AA. This work was also developed under the activities of project: Water Saving in Agriculture: technological developments for the sustainable management of

equivalent of tartaric acid. Total soluble solids

http://dx.doi.org/10.5772/intechopen.80365

69

to reach the desirable level of 6–7 mg L−<sup>1</sup>

solids, and anthocyanins.

**5. Conclusions**

effects.

orchard.

**Acknowledgements**

The use of irrigation in these increasingly stressful environments is a mitigating solution to maintain quality in wine production, minimize the most serious risks of drought damage, and in extreme cases, guarantee plant survival [151, 166].

Under RDI, plant water status is maintained within limits of deficit during certain phases of the seasonal development, normally when fruit growth is least sensitive to water reductions [167]; then, RDI at early stage of grapevine development looks more promising than in later stages. RDI has become widely adopted in the production of wine grapes in arid and semiarid areas [168] and several works have shown that it brings better results than simple DI or FI.

The demand for vineyard irrigation is on the rise as climate becomes more stressful but water is scarcer and the competition among stakeholders becomes acute, factors that require an improvement in the efficiency of water use.

In Alto Douro region, the highest water use efficiency (WUE) was reached in rainfed grapevines at expense of yields that were economically unsustainable because the benefits of irrigation were disproportional to the amount of water necessary to bring them about [152, 169]. To strike a balance between yields, berry quality and WUE, it is advisable to impose a moderate stress before veraison but after fruit setting. Pre-veraison RDI compared to SDI reduces vine water use and increases the canopy WUE, decreases the berry polyphenolic but might lower the financial return due to lower yields [170].

#### *4.3.3. Effect on berries quality*

There is no consensus among the various authors regarding the accumulation and concentration of important metabolites because it depends on skin to pulp ratio in berries [171] as smaller berries favor their concentration in the must. The soluble solids that determine the alcohol content in wine, was found to be more concentrated in grapevines subjected to SDI than in rainfed or abundantly irrigated plants [172], while others found a lower concentration under very restricted DI [153] or did not find any significant difference in their concentration [173]. These contradictory results might be related to the accuracy of vine water status monitoring necessary to regulate and manage the physiological changes imposed to the vines by DI [83]. In other words, DI might be beneficial if an accurate control of water deficits is exerted [94].

Studies have shown that changes in grapevine water status, at selected and critical phenological stages, are as important as the amount of water applied on influencing vegetative growth, yield, and fruit metabolism [40]. Experiments with DI of "Tinta Roriz" (Tempranillo) carried in Alto Douro (Portugal) [152, 166] showed that RDI was effective to increase the yields and also induced higher concentration of organic acids in the musts but insufficient to reach the desirable level of 6–7 mg L−<sup>1</sup> equivalent of tartaric acid. Total soluble solids and the concentration of glucose and fructose decreased as the rate of irrigation increased, mainly if water was applied after veraison. Irrigation had no influence on pH, anthocyanidins and flavonols of the must when compared with rainfed grapevines, but the effect was negative upon the polyphenol index, the total anthocyanins, and the color intensity. The adverse effects of irrigation were mitigated when vines were deficit irrigated between flowering and veraison followed by no irrigation till harvest. Some of these results were corroborated by other authors [81, 174]. The experiment also showed that rainfed vines produced musts with attributes very desirable for high-end wines but the yield was too low (as little as 300 g per plant) to guarantee a satisfactory economic return. RDI can result in substantial improvements on fruit quality through decreasing yield and berry size [94] and has a positive effect over synthesis and concentration of phenolic compounds, soluble solids, and anthocyanins.
