Deficit Irrigation as a Strategy to Save Water: Physiology and Potential Application to Horticulture

Jourmal of Integrative Plant Biology 2007. 49 (10): 1421-1434.Invited Review.Deficit lrigation as a Strategy to Save Water: Physiologyand Potential Application to HorticultureJ. Miguel Costal,2, Maria F. Ortuio1 and M. Manuela Chaves1.2*(Instudo Supartor de Agronomia, Universidade Tecnica de Usboa, Tapada da Ajuda, 1349-017 Lisboa, Portugal;2Laboratorio de Ecofsiologiag Molecular, Instuto de Tecnologia Quimica B Biologica, Apartado 127, 2780-901 Deiras. Portugal)AbstractWater is an increasingly scarce resource worldwide and rrigated agriculture remains one of the largest and most inefficientusers of this resource. Low water use efficiency (WUE) together with an increased competition for water resources withother sectors (e.g. tourism or industry) are forcling growers to adopt new irigation and cultivation practices that use watermore judiciously. In areas with dry and hot climates, drip irigation and protected cultivation have improved WUE mainlyby reducing runoff and evapotranspiration losses. However, complementary approaches are still needed to increase WUEIn Irigated agriculture. Deficit irigation strategies like regulated deficit irigation or partial root drying have emerged 8potential ways to Increase water savings in agriculture by llowing crops to withstand mild water stress with no or onlymarginal decreases of yield and quality. Grapevine and several frult tree crops seem to be well adapted to deficit irigation,but other crops like vegetables tend not to cope so well due to losses in yield and quality. This paper alms at providing anoverview of the physiological basis of deficit irigation strategles and their potential for horticulture by describing the majorconsequences of their use to vegetative growth, yield and quality of dfferent crops (ruits, vegetables and omamentals).Key words: defict imigation; hrtculture, partial rootzone drying. regutated defncit irigation; water saving.Costa JM, Ortuno MF, Chaves MM (2007). Deficit irigation as a strategy to save water: Physiology and potential aplication to hortiulture, J. Integr.Plant Biol. 49(10), 1421-1434.Available onlne at www blaowlsyoyrgrconmo/nis/c/.ib www. jipb.netis commonly associated wth the image of iefficiency. Thiscreased consumption, mismanagement and pollution. The pre-derives from a poor 'irigation water use eficiency,' understooddicted increase of dry days per year for many areas of the globeas the ratio between the irigation water absorbed by the cropwill further exacerbate the probiem (Pelit et al.1999; IPPC 2001;and the amount of water actually withdrawn from its source forLuterbacher et al. 2006). The agricultural sector contributesirigation purposes. The increasing demand of water resourceslargely to this unsustainable situation. Irigated agniculture isand limited ailbility makes water an increasingly valuablea major consumer of water and accounts for about two thirds ofcommodity. This is particularly true in regions where irigatedthe total fresh water diverted to humanuses (Fereres andEvansagriculture coexists with sectors like tourism and industry or2006). In the global debate about water scarcity, agriculturewhere urban growth is high. The Pacifc Northwest region inthe USA, the provinces of Almeria or Murcia in southeast Spainor the Shandong province in northem China Plain are goodReceved2 Dec 2006 Accepled 25 May 2007examples of this situation (Carvalho 2000; Costa and HeuvelinkMF Ortuno was granled a Postdoctoral research fllowship from the2004; Leib et al. 2006; Blanke et al. 2007; Downward andSpanish Ministy of Education and JM Costa was supported by a post.Taylor 2007). The agriculure sector is expected to lose thedoc flowship granted by Fundac8o para a Cienca e Tecnologia (FCTcompetition for water resources because it is less profitable(ref. POCI2010/SFRHBP014498/203). The WATERWEB project providedthan other sectors and because governmental restrictions willfunde for research in grapevine.force growers to reduce the use of irigation water."Author for corespondence.As a resut, improving crop water-use effciency {WUE) hasTel: + 351 21365 3415;been a mater nf ronrpm tn resarchers and agronomists inFax + 351 21385 3238;recen中国煤化ILterms of instantaneousE-mail: .measCNMH GFn gain per water loss◎2007 Institute of Botany, the Chinese Academy of Sciencesefhciency over timedoi: 11111 1672 9072 2007 0556.x(expressed as the ratio of biomass accumulation or harvested1422 Jouma/ of ltegrative Plant Biology Vol. 49 No. 102007yield to water use) (Bacon 2004). The WUE in the agriculturalan excessive application of water suppresses the advantage ofsector has been slowly improving due to the use of genotypesusing RDI and results in higher costs of water, while a lowerwith increased WUE (Condon et al.2004) and due to adoptionofwater aplication may resultin severe lsses ofyield and quality,innovative cutiation and imigation pratices (e.g. drip iriation,mainly if a sudden increase in temperature occurs (Jones 2004).use of imigatin calendars based on the depth of water table andAn altemnative strategy to RDI is partial root drying (PRD).soil salinity, reuse of wastewater) (Chaves et al.2003; PereiraPRD involves exposure of roots to altermate drying and wettinget al. 2006). Drip irigation, mulching and protected cultivationcycles and enables plants to grow with reduced stomatal con-have contributed to improve WUE in agriculture by sgnifiantlyductance but without signs of water stress (Zhang et al. 1987;reducing runoff and evapotranspiratinlosses (Stangllinietal.Davies et al.1994; Santos et al. 2003; Kang and zhang 2004).2003; Jones 2004; Kimak and Demlntas 2006). MediteraneanThis tehnique is based on plantroot to shoot chemical signalingcountries like Israel or Spain led developments in drip imiationthat influences shoot physiology and it can be operated in drip-and cultivation under plastic in the past decades, but Chinaorfurrowimigated crops. Theoreically, roots of the watered sldehas been strongly inveting in these techniques. China hasof the soil will keep a favorable plant water status, while dehy-recently emerged as the world's largest producer of greenhousedration on the other side will promote the synthesis of hommonalvegetables and omamentals (close to 2 million ha) and hassignals, which will reach leaves via the transpiration stream andabout 15 milin ha using plastic mulches (Costa and Hewvelinkfurther reduce stomatal conductance. This will decrease water2004). However, the use of drip imigation remains too restrictedloss and vegetative growth and increase WUE (Dry et al. 1996;(Blanke et al. 2007) suggesting that WUE can stil be optimizedDavies et al. 2000). The plant homone abscisic acid (ABA) isby adoption of more efcient imigation practices.a compound that plays a role in stomatal closure as soil driesDeficit irigation strategies have the potential to optimize(See Davies and Zhang 1991 or Dodd 2005 for a review. Thewater producity in horticulture. Nevertheless, the efects ofPRD strategy may also increase root growth at deeper layersdeficit irigation on yield or harvest quality are crop-specific.of the soil as it has been described for grapevine (Dry et al.Knowledge of how dfferent crops cope with mild water deficits2000b; Santos et al.2005) orin overall root system, as shown foris the basis for a successful application of defcit irigation intotomato (Mingo et al.2003) PRD strategies have also resuted inpractice. Our aim is to provide an overview of the physiologicalhigher xylem pH (Devies and Zhang 1991; Dry et al. 1996; Drybasis of deficit imigation strategies and their potential applicationand Loveys 1999; Stoll et al. 2000) and lower cytokinins levelsto some of the most important horticultural crops.(Stoll et al. 2000; Davies et al. 2005) which restricts stomatalopening. The PRD may also bring about other benefts tothe crop besides higher WUE. It can infuence carbohydratesThe Concept of Deficit lrigation and itspartitioning between the dfferent plant organs and affect thePhysiological Backgroundquantily and quality of the harvest (Kang and Zhang 2004). Apractical inconvenience of PRD is thatit is obliges to use doubleDeficit irigation strategies deliberately allow crops to sustainthe amount of tubes than RDI or DI, increasing istaltionsome degree of water defcit and sometimes, some yield reduc-xosts. Nevertheless, the underying causes of PRD functioningtion with a sinifcant reduction of imigation water. The cassic are sil a matter of dision. Bravdo (2005) stated that itdeficit imigation strategy (DI) implies that water is suppliedis not possible to have absolute control of root drying underat levels below full evapotranspiration (ETc) throughout thefield conditions and that hydrauic redistibution from deeperseason. The other two main deicit imigation strategies based to sallower roots may prevent the clear results that can beon the physiologial knowledge of crops response to waterobtained in potted plants. Other authors suchas Gu etal. (2004)stress, are regulated deficit irigation (RDI) and partial rootzoneargued that the amount of water used rather than the applicationdrying (PRD). The foremost principle of the RDI technique issystem can explain the effects of PRD.that plant sensitvity to water stress is not constant duing thegrowth season (cycle) and that intermitent water deficit duringspecic periods may beneft WUE, increase water savings andStomatal Regulation and Water Useeven improve harvest quality (Chalmers et al. 1981; McCarthyEfficiencyet al. 2002; Loveys et al, 2004; Cameron et al. 2006). In theRDI strategy, irigation is used to maintain plant walter stalusThe regulation of stomatal aperture is a central process towithin certain limits of deficit (with respect to maximum waterdetermine WUE of plants. Given the linear relationship betweenpotential) during certain phases of the crop cycle, normally whenstom中国煤化工Inder a constant vaporfruit growth is least sensitive to water reductions (Marsal et al.pressnon-inear relationship2002; Kang and Zhang 2004). The major disadvantage of thebetweMHC N M H G photosynthetic rate,RDI is that it is required lo maintain a plant's water status withinlower stomatal aperture may improve water use efciencynarrow imits,s which is dfcult to achieve in practice. Inthis way, (Chaves et al.2002).Deficit Imigation Physiology and Aplication to Horticulture 1423Table 1. Summary of the major factors influencing leaf stomatal conductance to water vapour and CO2 with a non-exhaustive list of referencesFactorsReferencesGenotype- SpeciesJones 1992; Bunce 1996; Bemachi et al. 2002; Chaves et al. 2002; Herrick ot al 2004.Leaf morphalogy (stomata densityand size, sun/shade leaves)-Leaf ageEnvironmental- lIradianceStalfet 1962; Zeiger 1983; Morison and Gfford 1983; Morison 1987; Zeiger et al. 1987; Honor et al.1995; Maroco et al.1997; Assmann 1999; Correla et al. 1999; Lasceve et al. 1999;9 McAinsh et al.2002; Maheralil et al. 2003; Talbot et al.2003; Ainsworth and Rogers 2007.. Light qualtly (bluelred)- Air temperature. Relative humidity. VPD. Wind speed. Gaseous pollutantsPhysiological. Leaf turgor, plant water statusCummins et al.1971; Davies and Mansfield 1987; Gollan et al. 192; lrving et al 1992; Jones 1992;Talbott and Zeiger 1996; Schroeder et al 2001; Merlot et al.2002, 2007; Klein et al.2003.. Hormones (ABA, cytokinins, auxin). Sugar accumulation. lons (Ca2+, K+)ABA, abscisic acid; VPD, vapor pressure deficit of the air.Stomata are bound by two guard cells that are sensitive tothe VPD increases. Franks et al. (1997) found a decrease indifferent types of signals either environmental (light, humidity,the steady state leaf transpiration rate with increased VPD,temperature, CO2) or physiological (phytohormones, calcium)which was reversible and independent of leaf water status.(Table 1). The environmental factors will act directly or idirectlyThere are also reports indicating a direct effect of VPD onon stomatal aperture, together with circadian rmythms, leaf waterstomatal regulation for woody plants (Franks and Farquharstatus and xylem-born signals (e.g. cytokinins, ABA) and at any1999; Maherali et al. 2003). High CO2 concentrations reducemoment all of these factors are integrated to deliver a particular stomatal senstivity to VPD (Bunce 1996), whereas water stressstomatal aperture (Webb and Hetherington 1997; Bacon 2004).tends to increase it (Eamus and Shanahan 2002). StomatalMaximum stomata aperture is known to occur under iradiancesresponse to VPD depends on the species as well (Bunce 1996;larger than 400 umolm2 per s (PAR) (Jones 1992). Part of Chaves et al.2002).the stomatal response to light results from a decrease of theintercellular CO2 concentration but guard cels are known torespond to blue (436 nm) and red light (681 nm) (Zeiger 1983).Soil Versus Leaf Water Status andThe effects of termperature on stomatal behavior are closelyStomatal Closurerelated to metabolism, enzymatic activity and hormones but alsoto extemal plant factors such as air vapor pressure. In general,Stomatal dosure and leaf growth inhibilion are among themaximal stomata conductance can be achieved at20 40 °C andearliest plant responses to drought leading to diminished wateris restricted by very low (5 °C) or extremely high temperatureslosses (Shulze 1986; Chaves 1991; Chaves et al. 2002). In(45 °C) (Stalfet 1962; Jarvis 1976). These limits are species-general stomata are not sensitive to changes of leaf waterdependent.potential (4) until a certain threshold is exceeded. Moreover,The diferencne of water vapor pressure between the leaf inte-there is strong evidence that leaf conductance responds earlierrior (100% vapor pressure) and the air vapor presure (variable)to soill water content than to leaf turgor (Davies and Zhang(laf-to.air vapor pressure deficit-LVPD) is another factor infu-1991;中国煤化工t dose in rsposeencing stomatal opening and closure. Stomata respond drectyto dryil:atus is maintained atto changes in the evaporative demand rather than to changes high tlMYHC N M H Got experiments wherein the relative humidity (Monteith 1995; Maroco et al. 1997).plants were grown with part of their roots in drying soil (GowingStomatal conductance of several plant species decreases as et al. 1990). Further evidence showed that stomatal closure is1424 Joumal of Integrative Plant Biology Vol. 49 No. 10 2007mediated by homonal signals (ABA) traveling from dehydratinghave been investigated for several horticultural crops, namelyroots to shoots (Davies and Zhang 1991; Bacon et al. 1998;grapevines, orchard fuit trees and vegetables (Goodwin andSobeihetal. 2004; Dodd 2005). The signaling pathway riggeredBoland 2002; Kang and Zhang 2004; Bravdo 2005; Fereres andby ABA in guard cells is one of the better understood pathwaysSoriano, 2007). The advantages of deficit irigation practicesin plants (Schroeder et al. 2001). Substantial progress has beenfor production of leaf vegetables are less clear than for fruitmade in the understanding of signal transduction pathways ofcrops (Jones 2004). However, deficit imigation practices can beABA by screening and characterization of ABA mutants withincreasingly justifled in order to save water, improve nitrate usealtered stomatal response to drought (Merlot et al. 2002).eficiency, minimize leaching of nutrients and biocide or in viewOther hormones are likely to act together with ABA or aloneof higher water prices.on stomatal regulation. For example, under soil water deficit,the increase in aytokinin concentration in the xylem decreasedstomatal sensitivity to ABA and promoted stomatal opening(Wilkinson and Davies 2002), whereas a decrease in cytokininGrapevine (Vitis vinifera L.) is grown worldwide and about 55%levels increased stomatal closure (Stoll et al. 2000; Daviesof its total area is located in Europe (Table 2). Grapevine is oneet al.2005). Other hormones belonging to the group of auxinsof the wl-adapted crops to the South European Mediteraneanwere found to stimulate stomatal opening (Davies and Mansfieldlimate. However, the combined effect of drought, high air1987).temperature and evaporative demand during summer, has ofenXylem sap pH may also infuence stomatal conductancelimited grapevine growth yield and quality of wine production inunder soil water deficit (Schurt et al.1992; Wilkinson and Daviesthe region (Escalona et al. 1999; Chaves et al.2002). Imigation1997, 2002; Netting 2000). The pHof the xylem sap, and therebyhas been adopted as a practice to minimize the problem and itof the leaf apoplast, becomes more alkaline in response tohas become common in modem Mediterranean viticulture undersoil drying. The net result is an accumulation of ABA to phys-certain restrictions.iologialy active concentrations in the leaf apoplast adjacentThe use of irigation in wine production has been alwaysto guard clls, which will induce stomata closure (Wlkinsonan object of large debate. On one hand, smal water supple-and Davies 1997; Bacon et al. 1998; Loveys et al. 2004).ments may inrease yields and maintain or even improve beryquality (Mathews and Anderson 1989; Reynolds and Naylor1994; Santos et al. 2003, 2005). On the other hand, irigationDeficit lrigation: Water Use Efficiency,may promote excessively vegetative growth, decrease bery'sCrop Growth, Yield and Qualitypigments (color), decrease sugar content (f applied later inthe season), and further decrease wine qality (Bravdo et al.Major horticultural production areas are located in hot and dry1985; Matthews et al. 1990; Dokoozlian and Kliewer 1996;climates (e.g. Mediteranean) where high light, high tempera-McCarthy 1997; Esteban et al.2001). Moreover, a larger canopytures and high VPD often co-occur with low soll water content.leaf area increases transpiration losses and disease problems,Deficit irigation strategies may help to save more water andmainly fungal disorders (Dry et al. 1996; Dry and Loveys 1998;optimize or stabilize yields and quality in these areas and theyBehboudian and Singh 2001).Table2. Culivated area (illin hm2) and production (illin ton) of grapes in the diferent continents relative to 2005 (FAO 2006)Continent/CountyArga (ilin hm?)Production (illin tons)Europe4.0629.8ltaly0.848.8France0.856.8Spain0.955Portugal1.Asla16.8China0.455.7America0.9113.0USA0.386:Africa0.343.2South Africa0.12中国煤化工1.2Oeania0.17MHCNMHG2:2.0Autralia0.15World7.3565.8Deficit Imigation Physiology and Application to Horiculture 1425In order to minimize the inconvenience of imigation andmaximize WUE in wine production, the response of grapevines350.to deficit irigation strategies such as RDI and PRD has been300investigated (Stone et al. 2001; McCarthy et al. 2002; Santosetal. 2003; Cife et al. 2005; Souza et al 2005). A major efecet250of cotolled mild soil water deficits is a decrease in stomatal00 tclosure with a slight decrease of net assimilation (Chaves and8 150Oliveira 2004). As a consequence, a higher intrinsic WUEais often found under deficit imigation conditins as previously100described. Our own field studies using the cultivars 'Moscatel,5('Castelao' and 'Aragonez' showed that PRD (iriation at 50%ETc altematively in each side of the root system) and theFNDI PRDconventional DI (irigation at 50% ETc divided by the two sidesof the root system) as compared to full irigated grapevinesB(FI, 100% ETc) promoted WUE, either in the short-term (asbxpressed by the ANgs ratio) (Figure 1A) but also in the long-14term, as shown by the increase in 13C in plant tisues, especially12in berries (Souza et al. 2003, 2005). Crop water use eficiency. 10was also significanty higher in PRD and DI as compared to FIo8(Figure 1B). Such increments in WUE and water savings are inline with studies from other groups for other grapevine cultivars6and/or locations (Davies and Zhang 1991; Dodd et al. 1996;Davies et al. 2000; Dry et al. 2000a,b; Stoll et al.2000 Loveyset al. 2004). Athough the diferences on stomatal closure andWUE are subtle between PRD and DI (Souza et al. 2003;PRDSantos et al. 2003), we found that PRD tends to induce areduction of vigor translated in smaller canopy leaf areas andless pruning weight (Souza et al. 2003; Santos et al. 2005)Flgure 1. (A) Itinsic water use eficiecy (Ag.) and (B) crop waterusewhich agrees with previous findings (Loveys 1984; Davies andeffciency (rield bermyliter of imigation water) for 5-year-old grapevinesZhang 1991; Dodd et al. 1996; Dry et al.1996; Davies et al.(Vits Vinifera L) cv 'Aragonoz' (syn. Temraillo') grafted on the 11032000; Loveys et al. 2000). The decrease in vegetative growthPaulsen rostock and subjected如o four inigation treatments: (1) partial-caused by PRD leads to better exposure of bemy dlusters toroot drying (PRD), 50% of the ETc peridically supplied to only one sidesolar radiation and may improve fruit quality (Santos et al.2005,of the root system with the other llowed to dry. and sides altermated2007). In addition, growth inhibition occurs in spite of similarevery 15 days; (2) deficit imigation (DI)， 50% of the ETc suppliedor even improved water status in PRD as compared to DI.simultaneously to both sid的s of the row (25% to 的ch side); (3) non-which suggests that vegetative growth is being regulated byImigated (NI), non lrigated but rain-fed: and (4) ful imigated (F).100%of the ETc splied to both sides of the row, half to each side. Valuesnon-hydraulic mechanisms (Chaves and Oliveira 2004).The RDI strategy has also been shown to be a viable practiceare means士SE (n= 3). iferent ltters denote sinificant diferencresto control excessive vigor and improve bermy quality (Bravdo(P<0.05) by the Duncan's test. Gas exchange measurements wereet al. 1985; Matthews and Anderson 1988). The effect of thecamied out at 360ppm CO2, 1200 umol quanta/m2 per s (10% blueRDI depends however, on the phenological stage and onlghth, wth temperature set at 25°C, using a LiCor-6400 portablethe severity of the stress imposed (Hardie and Considine 1976).photosynthesis system. Measurements were camied out in summerThe way the RDI strategy is applied in commercial vineyards(24 August 2005) on mature leaeves from the intermediate part of theis not uniform. In Mediterranean conditions it is common tocanopy and at the sunlt slde.apply water deficit during the final phases of grape development(William and Matthews 1990), whereas in Australia the commonimposed either before or after veraison, but mainly when thepractice is to apply less water earty in the season (McCarthydeficit was imposed before veraison (Matthews and Andersonet al. 2002). The aim in the first case is to avoid water stress1989). Fower bermios per cluster, fewer clusters per vine andduring the ripening stage whereas in the second case the aimdecn中国煤化iwer yields under suchis to contro bery size.001989). In tum, PRD ir-Regulated deficit imigation strategies have the potential torigatiYHC N M H Gily cause no signifcantreduce yields, although this depends on the timing of applicationyield reduction, even though the amount of imigation water is(McCarthy et al. 2002). Yields were reduced by water deficitssignificantly reduced (McCarthy et al. 2002; Kang and Zhang1426 Jourmal of Integrative Plant Biology Vol.49 No. 10 20072004; Bravdo 2005). Mild stress imposed by PRD (at 50% ETc)yield or fruit size (Kang et al, 2002). The RDI strategy in tum wastreatments had no negative effect on the yield of the cultivarsuccessfully aplied to field-grown plants of the cultivar *Barlett''Castelao' (Santos et al. 2005).especially if water deficits were imposed during stage I of fuitdevelopmentwhen cell division occurs (Mitchell et al.1989). Thequality due to an increment in the contents of anthocyanins andRDI strategy permitted to save water, limit vegetative growthtotal phenols (Dokoozlian and Kliewer 1996; Santos et al.2005).without afcting fuit growth. RDI was also tested on plants ofThis is related to less dense canopies and better exposure tothe same pear cultivar, but grown in containers and decreasedlight. Nevertheless, Keller and Hrazdina (1998) found no difershoot growth and to a lesser extent fruit growth (Marsal et al.ence in the anthocyanin concentration at 20% or 100% sunlight2000). The authors suggested that the effect of RDI on canopyinterception for the cultivar 'Cabemet Sauvignon', suggestinggrowth can be more positive when vigorous rootstocks are used, .that above a given threshold, light is not the major factor limitingwhen soils are fertile or plantation density is very high. On thethe synthesis of anthocyanins.other hand, o'Conell and Goodwin (2004) found for the culivarWilliams Bon Chretein' that PRD stategies (at 50% of ETc)resulted in water-stressed plants.Regulated defcit irigation was also tested in peach (PrunusFrult treespersica L.) by various authors (Chalmers et al. 1981; MitchellDeciduousand Chalmers 1982; Li et al. 1989; Boland et al. 1993; GironaIlmigation in fruit trees provides protection against droughtet al. 2005) who showed in general an increase in WUE andand contributes to increase or stabilze production (Fereresa reduction in vegetative growth, without a negative effect onand Evans 2006). DI strategies have been developed for highyield. Similar ffects of defit imigation strategies on WUE anddensity orchards of tree crops such as apple, pear and peachvegetative growth were described for other crops like the Asianmainly to balance vegetative and reproductive growth (Goodwinpear (Pyrus serotina L.) and prunes (Prunus domestica L.)and Boland 2002; Loveys et al. 2004). For these crops the(Goodwin and Boland 2002).major effect of deficit imigation is to reduce vegetative growthIn nut crops like almond (Prunus dulcis Mil.), RDI decreasedwith minor changes on fruit development (Goodwin and Bolandkern yields by about 10 to 20% but improved WUE and water2002; Loveys et al. 2004). Deficit imigation strategies cansavings up to 50% as compared to FI (Romero et al. 2004).be also a cheaper and equally eficient altermative to branchImigation regimes infuence the incidence of diseases in nutmanipulation, shoot and root pruning or hormonal treatmentscrops and the principle of reducing inigation before harvestto control vegetative growth and diminished shading (Goodwinto control hull rot caused by Monilinia fructila and Rhizopusand Boland 2002). Additionally, it reduces water use as well asspp. is well established (Ogawa and English 1991) Studies withthe risks of nutrient or biocide leaching.almond showed that DI imigation (at 70 -80% ETc) decreasedPublished reports on the efects of deficit imigation strategiesyields but lessened the incidence of hull rot as compared to FIon yield and quality of fruit crops is however, not conclusive.plants (100% ETc) (Teviotdale et al. 2001). The yield reductionsIn apple (Maus domestica L.) for example, RDI was shownobserved under DI conditions were atributed to smaller kemelto decrease yield and frult size irespective of the timing ofsize but were considered marginal if compared to the benefitsapplication (Landsberg and Jones 1981; Ebel et al. 2001;due to reduced hull rot incidence (Teviotdale et al, 2001).Mpelasoka et al. 2001). More recent results with the cultivars'FUjI' and 'Gala' showed that DI and PRD that pemitted watersavings of about 45- -50% and 25- -75% respectively, had noEvergreeneffect on yield nor on fuit size as compared to the F|(100% ETc)Deficit imigation strategies have been progressively applied toplants (Einhom and Caspari 2004; Leib et al. 2006). Studiesolive trees (Olea europea L.) in particular in the Medterraneanwith the cultivar 'Braebum' showed that the classic DI (50%Basin where there is an ongoing shift from traditional rain-of the control imigation frequency) reduced water use by 60%fed culivation to irigated plantations (Testi et al. 2006). RDIas compared to the control and had no significant efects on一strategies successlly reduced water use in dfferent cultivarsgross yield (Mpelasoka et al.2001). DI advanced fruit ripening,and growing locations (Alegre et al. 1997; Goldhamer 1999;increased flesh firmness and increased total soluble solidsWahbi et al. 2005). PRD (50% ETC) resulted in higher WUE in(TSS) and aroma volatiles both at the nipening phase and afterplants of the culivar 'Picholine marocaine' due to lower stomatalstorage (Mpelasoka et al. 2001; Mpelasoka and Behboudianconductance and a non-significant reduction in photosynthesis2002).(Centrn中国煤化工3S ofthe same culivarIn pear (Pyrus communis L), feld experiments using treesshowed a slight decrease ingrown under flood imigation and a shallow water table, showedvegetaYHCN M H Gd to the FI trealtmentthatPRD can save 23 to 52% ofthe imigation water as compared(Wahbi etal.2005) butyield was higher thanthe one obtained forto fully imigated trees, without any or only marginal reduction innon-imigated (NI) plants. Identical results were reported for the1428 Joumal of Integratve Plant Biology Vol. 49 No. 10 2007and the amount of marketable fruits were identical to the controland Demintas 2006) or cucumber (Cucumis sativus L.) (Maowith only a 6% reduction in water use. However, when applyinget al. 2003) showed higher WUE when subjected to verythe PRD from appearance of the frst truss to fuit set or fromfruitmoderate water deficits (80 -90% ETc) in parallel with losses inset to harvest, yield losses reached 1.8kg of fesh weight peryield and fruit weight. Combination of deficit irigation strategiesplant as compared to FI (Zegbe et al. 2006). The incidence ofwith mulching was suggested to be a possible way to improveblossom- end rot was significanty higher in PRD plants treatedWUE and minimize the negative efcts of deficit irigation onbetween fuit truss and fruit set (Zegbe et al. 2006). Fuitsthe yield of cucumber grown in open felds (Kimak and Demitasfrom plants subjected to PRD since fruit set until harvest, had2006).significanty higher TSS than the other tealments and savedGlasshouse trials with hot pepper (Capsicum annum L) Cvmore water (up to 25%). It is possible that water savings and'Ancho St. Luis' have shown that PRD and DI (irigated withgains in quality may compensate the eventual losses in fresh50% of the volume of commercial imigation used as a control)and dry weight of fuits especialy in regions where water is anreduced total fresh weight of fruits by about 19% and 35%,expensive input (Zegbe et al.2006).respectively as compared to the control FI (Dorji et al. 2005).Fruit number was also reduced by 20% for plants subjectedto deficit imigatin, which was atributed to flower abortion justPotatolike was suggested for tomatoes (Pulupol et al. 1996; ZegbeAccording to Shock and Feibert (2002) the economic oppor-Dominguez et al.2003). Lower fuit load in DI plants might havetunities for using deficit irigatlon in potato (Solanum tuberosumfavored carbon partitining to fruits and increased the contentL.) are more limited than for other crops because potatoesin soluble solids by about 20%.have a shallow root system and are very sensitive to waterField studies with two culivars of watermelon (Citullusstress. Research has shown those yield and wber grades arelanatus L, 'Summer sweet 5244' and 'Super seedless 7187',considerably reduced by soil water deficits even when briefyshowed that deficit imigation practices reduced total marketableapplied (Lynch et al. 1995; Shock and Feibent 2002; Liu et al.yield by 15 to 36% and increased yield of small fuits (<5 kg)2006). The negative efect depends not only on the cultivarbut had no efct on fruit quality (lycopene content) (Bang et al.(effries and MacKerron 1993) but also on the phenological2004). The effects of deficit imigation on melon (Cucumis molophase. Severe reductions in tuber yield and quality occuredL.) seem to also be dependent on the timing of the treatment. Inwhen brief periods of water stress were imposed fllowin tuberfact, trials with the cultivar 'Piel de Sapo' showed that yield wasset (Lynch et al. 1995),particulaty reduced when defcits were applied during bloomingFabeiro et al. (2001) in tum, showed for the culivar 'Agria' that(Fabeiro etal.2002). In gartic (lium setvumL.) deficit imigationapplying moderate water deficit during growth and tuber bukinghad its most detrimental efet on yield when applied duringresulted in similar yields to fully imigated plants and that thethe ripening stage but when applied at the bulbifcation stagesmallest yields were obtained when deficitwas applied inthe lastit decreased both yield and quality (bulb size) (Cortes et apart of the growth cycle. Liu et al. (2006) showed no advantage2003).in using PRD (at 50% ETc) relatively to the conventional DIregarding biomass accumulation and WUE when it was appliedat the tuber itiation stage.Netheless, Nimah et al. (2000) emphasize the positive0mamentalseffect of deficit imigation on potato production, regarding waterCameron et al. (2004, 2006) found that deficit imigation (>50%and nitrogen savings, which could reach about 30%，FieldETc) has commercial potential to reduce excessive growth ofstudies with the cultivar 'Folva' showed that PRD (50- -70%several woody omamentals belonging to the genus CotinusETc) maintained tuber yields and increased irigation water useand Forsythia and to reduce water consumption by 50% toeficiency (IWUE) by 60% as compared to FI plants kept at field90% relatively to the irigation used comerailly. Moderatecapacity (Shahnazani et al. 2007). PRD significanty reducedwater deficits imposed by RDI (at 50% of the ETc) improvedleaf area index as compared to FI plants in line with findingscommercial crop quality. Shorter intemodes and shoots, andfor crops like grapevine (Stoll 时t al. 2000; Santos et al. 2003)identical number of primary shoots gave more compact plantsor tomato (Topcu et al. 2007). Aocording to Shahnazani et al.and suppressed the need for mid-season pruning (Cameron(2007) the advantage of PRO to FI resides in a better balanceet al. 2006). More severe water defcits (at <25% of the ETc)of photosynthesis versus transpiration and in a betteruse ofsoilresulted in leaf injury and consequenty lower quality (Cameronwater reserves due to a larger root system.etal |中国煤化工，imigated control) wereOther vegetablestesteMYHC N M H Gunsetr, a commercillyVegetable crops such as hot pepper (Capsicum annum L)relevant protea cltvar (ilber et al.2007) Short events of water(Kang et al.2001), egg plant (Solanum melongena L) (Kimak deficits had no negative efect on the flower head dimensionsDeficit Imigation Physiology and Application to Horticulture 1429nor on the number of marketable stems but resulted in too smallReferencesleaves, and thus on quality loss. Plants under continuous waterdeficit had the lowest total dry weights and the lowest proportionAInsworth EA, Rogers A (2007). 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