Effect of saline conditions on the maturation process of Clementine Clemenules fruits on two different rootstocks

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1 Instituto Ncionl de Investigción y Tecnologí Agrri y Alimentri (INIA) Aville online t Spnish Journl of Agriculturl Reserch 20 8(S2), S21-S29 ISSN: X eissn: Astrct Effect of sline conditions on the mturtion process of Clementine Clemenules fruits on two different rootstocks J. M. Nvrro*, A. Gomez-Gomez, J. G. Perez-Perez nd P. Boti Deprtmento de Citricultur, IMIDA. C/ Myor, s/n. 150 L Alerc (Murci). Spin The production of mndrins is importnt in the Mediterrnen re, where the continued use of sline wter reduces fruit yield nd modifies fruit qulity. Grfted trees of Clemenules mndrin scion on Crrizo citrnge nd Cleoptr mndrin rootstocks, two of the most common citrus rootstocks employed in this re, were irrigted with two sline tretments (control nd mm NCl). The fruit qulity ws studied through the lst two months efore the fruit hrvest. Slinity reduced oth the fruit numer nd the men fruit weight on Crrizo trees wheres no fruit weight reduction ws oserved on Cleoptr. The decrese of fruit weight on Crrizo trees is proly due to the lower wter content nd consequently the lower juice percentge. Although the sline tretment produced significnt differences in some fruit qulity vriles (shpe nd thickness indices) throughout the mturtion process, they were miniml t the hrvest time. Totl solule solids (TSS) were significntly higher in fruits from the sline tretments, proly due to pssive dehydrtion. It is lso possile tht de novo synthesis of sugrs occurred, since fruits from Cleoptr trees receiving the sline tretment hd similr wter contents ut higher TSS thn control fruits. The externl fruit colour indicted tht the sline tretment ccelerted the mturtion process; however, the mturity index showed tht the high cidity of these fruits delyed the internl mturtion with respect to the control fruits. Additionl key words: cidity; Crrizo citrnge; Cleoptr mndrin; fruit colour; mturity index; shpe index; totl solule solids. Resumen Efecto del riego con gu slin en el proceso de mdurción de los frutos de Clementin Clemenules L producción de mndrins es importnte en el áre mediterráne donde el uso continudo de gu slin reduce l producción y lter l clidd de los frutos. Ároles de mndrino Clemenules injertdos en citrnge Crrizo y mndrino Cleoptr, dos de los ptrones de cítricos más empledos en l zon, se regron con dos trtmientos slinos (control y NCl mm). Se estudió l clidd de los frutos en los dos últimos meses ntes de l cosech. L slinidd disminuyó tnto el número de frutos como el peso medio de los mismos en los ároles de Crrizo mientrs que no redujo el peso en los frutos de Cleoptr. Dos meses ntes de l cosech del fruto, los ároles Crrizo de los trtmientos slinos tuvieron frutos con menor peso que los del control, prolemente deido l menor contenido de gu y por tnto l menor porcentje de zumo. Aunque durnte el proceso de mdurción del fruto el trtmiento slino produjo diferencis significtivs en lguns vriles de clidd del fruto (índices de form y de espesor de cortez), ests diferencis fueron mínims en el momento de l recolección. Los sólidos solules totles (TSS) fueron significtivmente myores en frutos de los trtmientos slinos, prolemente deido un deshidrtción psiv. Tmién pudo producirse un síntesis de zúcres de novo, y que los frutos de los ároles de Cleoptr del trtmiento slino tuvieron igul contenido de gu pero myor TSS que los frutos control. El color externo del fruto indicó que el trtmiento slino celeró el proceso de mdurción; sin emrgo el índice de mdurez mostró que l lt cidez de estos frutos retrsó l mdurción intern respecto los frutos control. Plrs clve dicionles: cidez; citrnge Crrizo; color del fruto; índice de form; índice de mdurez; mndrino Cleoptr; sólidos solules totles. * Corresponding uthor: josefm.nvrro2@crm.es Received: ; Accepted: Arevitions used: ETo (reference crop evpotrnspirtion), Kc (crop coefficient), MI (mturity index), PTI (peel thickness index), TA (titrtle cidity), TSS (totl solule solids), Ψ x (xylem wter potentil).

2 S22 Introduction J. M. Nvrro et l. / Spn J Agric Res (20) 8(S2), S21-S29 Mteril nd methods The production of mndrins is economiclly importnt in south-estern Spin, where the climte is semi-rid with dry, hot summers nd high evportive demnd. The scrcity of wter resources in these semirid regions forces to growers to use low-qulity wters from quifers contining excessive concentrtions of solule slts. Citrus species hve een clssified s slt-sensitive crops (Ms, 1993), nd the continued use of sline wter reduces citrus fruit yield nd modifies the fruit qulity. Slinity decreses the fruit size nd modifies some fruit physicl chrcteristics such s peel thickness nd the percentges of juice, pulp nd peel (Primo-Millo et l., 2000; Moring nd Sykes, 2001; Grcí-Sánchez et l., 2003, 2006). Some internl qulity vriles re lso modified, such s totl solule solids (TSS), fruit cidity nd the mturity index (Primo-Millo et l., 2000; Moring nd Sykes, 2001; Grcí-Sánchez et l., 2003, 2006). It is well-known tht fruit qulity is lso influenced y rootstock (Cstle et l., 1993; Brry et l., 2004). Inherent rootstock differences ffecting plnt wter reltions re ssocited with differentil sugr ccumultion of citrus fruits, which re proposed s primry cuse of differences in qulity mong citrus rootstocks (Brry et l., 2004). The tree folige supplies crohydrtes to the fruit ut the rootstock determines the mount (Grdner, 1969). It is not cler how rootstocks exert their influence on the juice qulity of Citrus species, ut plnt wter reltions re importnt fctors in this (Cstle, 1995; Nvrro et l., 20). Crrizo citrnge nd Cleoptr mndrin, the most-common rootstocks employed in Spin, hve differing chrcteristics, resulting in different responses of qulity (Romero et l., 2006; Pérez-Pérez et l., 2008). These genotypic differences could ffect yield nd fruit qulity (Syvertsen et l., 2000; Brry et l., 2004; Koshit nd Tkhr, 2004). Recently, we found tht the response to drought stress of the fruit qulity of Clemenules mndrin trees grfted on Cleoptr mndrin or Crrizo citrnge differs (Nvrro et l., 20). In order to evlute the suitility of these rootstocks in semi-rid environment, we exmined the effect of irrigtion with sline wter on some importnt fruit qulity vriles during the lst phses of the fruit mturtion process for field-grown Clementine citrus trees grfted on Cleoptr mndrin or Crrizo citrnge, two rootstocks with differing sensitivities to slinity. The study ws crried out in Murci (southern Spin), on 11-yer-old citrus trees (Citrus reticult Blnco) cv. Clemenules grfted on two rootstocks, Cleoptr mndrin (Citrus reshni Hort. ex Tnk) nd Crrizo citrnge (Citrus sinensis L., Oseck Poncirus trifolit L.). The soil is n ridisol, with 27.9% cly, 33.5% lom nd 38.6% snd. The soil hd n orgnic mtter content of 0.71% (dry soil), n EC 1-5 (electric conductivity) of 0. ds m 1, 17.50% ctive CCO 3 nd ph of 7.6. The wether is Mediterrnen semi-rid, with high men dily solr rdition (> 200 W m 2 ), > 9 dily solr hours, men nnul ir temperture of round 17 C, scrce nnul rinfll t the experimentl site (283 mm) nd totl nnul reference evpotrnspirtion (ETo), clculted vi the Penmn-Monteith method (Allen et l., 1998). The wter pplied cme from the Tjo-Segur cnl, with ph of 8.99 nd n electricl conductivity of 1.0 ds m 1 nd contining (mmol L 1 ): C , Mg , K + 0.2, N + 3.9, Cl 3.0, SO nd HCO A drip line ws used in ech tree row, with three self-compensting drippers (4 L h 1 ) per tree, 0.75 m prt. The irrigtion schedule ws pplied weekly using the crop coefficient (Kc) of 1, 0.7 nd 0.6 during Jnury nd Ferury, from Mrch to June nd from July to Decemer, respectively, ccording to Amorós (1993) for mndrin trees in the Mediterrnen re, nd corrected y climtic dt t the experimentl site nd neutron proe mesurements. At the eginning of the experiment, the verge of shded re per tree ws similr for Crrizo nd Cleoptr, respectively; thus, the irrigtion volume pplied ws the sme. In 2004, the nnul ETo ws 1,255 mm nd the rinfll ws 434 mm, pplying the totl irrigtion volume of 691 mm nd 679 mm for control nd sline tretments respectively, in oth rootstocks. The experiment ws performed in trees hving fully-developed cnopy, with tree-spcing t 3 4 m. The lyout took the form of three completely-rndomised, selected plots. Ech tretment ws pplied to 9 trees (3 trees per tretment in ech plot). The tril involved two sline tretments, 0 nd mm NCl (0 nd 3.3 ds m 1, respectively), tht were pplied from Mrch until the hrvest of the fruits on the two rootstocks. The xylem wter potentil (Ψ x ) ws mesured fortnightly. One mture, fully-expnded lef from the outer cnopy, in the middle third of the tree, ws tken from

3 Slinity nd mturtion of mndrin fruits S23 6 trees per tretment. The leves were enclosed within foil-covered plstic nd luminium envelopes t lest 1 h efore the middy mesurement (McCutchn nd Shckel, 1992). The middy Ψ x ws mesured t noon (12:00-14:00), using pressure chmer (model 00; Soil Moisture Equipment Corp., Snt Brr, Cliforni, USA) nd following the recommendtions of Turner (1988). Fruits were hrvested on the 15 th of Novemer, when they reched their commercil size. Individul tree yield ws mesured in the 9 trees per tretment. The numer of fruits nd the totl fruit weight of ech tree were mesured. Some fruit smpling ws crried out from the end of phse II nd during ll of phse III of fruit growth (60, 48, 20 nd dys efore the hrvest). In ll cses, smple of 9 fruits per tree ws collected, rndomly, from the 9 trees per tretment, for nlysis of fruit qulity. The externl fruit colour ws mesured in the 9 fruits using tri-stimulus colour difference meter (Minolt CR-0 colorimeter), on three loctions round the equtoril plne of the fruit. The Hunter prmeters nd were used, nd colour ws expressed s the / Hunter colour rtio. Fruit weight nd the equtoril nd longitudinl dimeters were determined. The «Shpe Index» ws clculted s the rtio: longitudinl (equtoril dimeter) 1. Fruits were cut in the equtoril re nd the internl fruit colour ws mesured using the Minolt CR-0 colorimeter, t three loctions of the equtoril plne, nd expressed s the / Hunter colour rtio. Peel thickness ws mesured t three points nd the peel thickness index (PTI) ws clculted s Domingo et l. (1996) eqution: PTI = [peel thickness (mm) 200] [equtoril dimeter (mm)] 1 Fruits were squeezed nd the juice filtered for mesurements of the totl solule solids content (TSS) nd titrtle cidity (TA). All fruit frctions were seprted, weighed nd expressed s juice, peel nd pulp percentges. The TSS of the juice ws mesured t 25 C with digitl refrctometer (Atgo, Plette PR0) nd TA ws determined y titrtion with 0.4 N NOH nd phenolphthlein indictor (results re expressed s percentge of citric cid in the juice). The mturity index (MI) ws expressed s TSS/TA. For the fruit wter content determintion, four fruits per tree were hrvested t ech fruit smpling nd they were weighed fresh nd fter drying. The dt were nlysed using nlysis of vrince (ANOVA) procedures nd mens were seprted y Duncn s multiple rnge test, using the SPSS softwre pckge (SPSS for Windows, stndrd version, 1996). Results nd discussion Slinity decresed fruit yield for oth rootstocks due to oth lower fruit numer nd lower men fruit weight (Fig. 1 nd Tle 1). The fruit numer reduction ) 86 ) 0 c 90 c c Men fruit weight (g) Slinity * Rootstock ** Sl. Rootst. *** Slinity *** Rootstock ns Sl. Rootst. *** Figure 1. The influence of the slinity tretment nd the rootstock on the evolution of the men fruit weight () nd the fruit wter percentge () two months efore the fruit hrvest. Crrizo 0 mm NCl, open circles; Cleoptr 0 mm NCl, open squre; Crrizo mm NCl, closed circles; Cleoptr mm NCl, closed squre. The sttisticl nlysis refers to hrvested fruits. ns: no significnt. * P < ** P < *** P < Seprtion y Duncn s multiple rnge test t the 95% confidence level. H 2 O (%)

4 S24 J. M. Nvrro et l. / Spn J Agric Res (20) 8(S2), S21-S29 Tle 1. The influence of the slinity tretment nd the rootstock on Clemenules mndrin fruit yield vriles t the end of the experimentl period Rootstock Slinity Yield (kg tree 1 ) Fruit numer Crrizo 0 mm NCl ,321.9 mm NCl ,203.1 Cleoptr 0 mm NCl mm NCl Slinity (S) *** * Rootstock (R) *** * S R ns ns ns: no significnt. * P < *** P < Ψ x (MP) Slinity *** Rootstock ** Sl. Rootst. ** Figure 2. The influence of the slinity tretment nd the rootstock on the xylem wter potentil (Ψ x ) two months efore the fruit hrvest. Crrizo 0 mm NCl, open circles; Cleoptr 0 mm NCl, open squre; Crrizo mm NCl, closed circles; Cleoptr mm NCl, closed squre. The sttisticl nlysis refers to the lst dte. ** P < *** P < Seprtion y Duncn s multiple rnge test t the 95% confidence level. due to sline stress is well-descried in mndrin trees (Moring nd Sykes, 2001; Grcí-Sánchez et l., 2006) nd other citrus vrieties nd it hs een ttriuted to n norml fruit scission (Nieves et l., 1990, 1991; Dserg et l., 1991; Primo-Millo et l., 2000; Grcí- Sánchez et l., 2002). In other studies, the reduction of yield y slinity hs een relted with the lower fruit weight (Cerdá et l., 1986; Moring nd Sykes, 2001; Bomn, 2004). Slinity ppliction decresed the fruit numer for oth rootstocks, ut only for Crrizo rootstock were fruits of the slinity tretment smller thn control fruits (Fig. 1). Two months efore the hrvest, the slinity hd lredy cused mrked differences in the weight of fruits on Crrizo rootstock ut not for those on Cleoptr. These differences incresed until the hrvest nd the end of the experiment: the fruit weight from Crrizo decresed 26% with respect to the control wheres the weights of the fruits from Cleoptr trees were higher thn their respective controls. These low fruit weights oserved in fruits from Crrizo were due to oth, the lower wter content in the fruit (Fig. 1) nd the lower dry mtter content since this effect ws lso oserved in the fruit dry weight (dt not shown). However, the wter content of fruits on Cleoptr did not chnge with NCl ppliction. Slinity tretment decresed the wter potentil in trees irrigted with sline tretments for oth rootstocks (Fig. 2). The higher wter stress chieved in Crrizo thn in Cleoptr trees from the eginning of the experimentl period could e the consequence of their different slinity tolernce. Moreover, Cleoptr is lso etter soil wter extrctor, mintining etter tree wter sttus thn Crrizo (Romero et l., 2006). Therefore, rootstock differences in root system morphology (higher root density or deeper root system in Cleoptr compred to Crrizo) could determine some shoot chrcteristics (wter, nutrient, nd cron udgets, disese resistnce, nd plnt growth regultors). These citrus rootstock chrcteristics imprt some stress tolernces tht re usully dominnt in determining tree responses to environmentl stresses (Syvertsen nd Lloyd, 1994). Shpe index decresed with fruit mturtion (Fig. 3), regrdless of tretment. Before the hrvest, fruits from Cleoptr trees receiving the sline tretment hd more-rounded shpe thn control fruits. However, t hrvest, no differences were found etween tretments or rootstocks. For Cleoptr fruits, the PTI ws lower with the sline tretment two months efore the hrvest; however, t the hrvest time no differences were found etween rootstocks or tretments (Fig. 3). An increse of the PTI due to slinity hs een found for Vlenci ornge grfted on Cleoptr rootstock (Frncois nd Clrk, 1980), in Nvelin ornge nd Clementin de Nules (Primo-Millo et l., 2000). Also, n increse of the peel thickness due to slinity hs een found in Vern lemon nd Str-Ruy grpefruit (Nieves et l., 1991; Porrs et l., 2000). The externl colour of citrus fruits is one of the min ttriutes of qulity nd mjor vrile for consumer cceptnce. The fruit colour is expressed s / since this rtio hs high correltion with the visul ppre- c

5 Slinity nd mturtion of mndrin fruits S25 ) ) Shpe index Peel thickness index Slinity ns Rootstock ns Sl. Rootst. ns 6 Figure 3. The influence of the slinity tretment nd the rootstock on the evolution of the shpe index () nd the peel thickness index () two months efore the fruit hrvest. Crrizo 0 mm NCl, open circles; Cleoptr 0 mm NCl, open squre; Crrizo mm NCl, closed circles; Cleoptr mm NCl, closed squre. The sttisticl nlysis refers to hrvested fruits. ns: no significnt. cition of the fruit colour (Stewrt nd Wheton, 1971) nd represents the colour vrition from yellow to ornge. The results show tht the rootstocks hd no effect on the externl colour of the fruits (Fig. 4). However, t the end of the mturtion process, fruits from the sline tretment hd 25% higher / rtio thn in the control fruits. During the mturtion process the peel colour chnges mrkedly, since chloroplsts (contining crotenoids nd chlorophyll) re trnsformed into chromoplsts (hving only crotenoids), tking plce strong modifiction of chlorophyll nd crotenoid levels nd mssive ccumultion of crotenoid (Rodrigo et l., 2004). As the / rtio is negtive for green fruits nd positive for ornge fruits, the higher / rtio of sline fruits could show n pprent dvnce in their mturtion process with respect to control fruits (Fig. 4). With respect to the internl colour, only fruits from Crrizo trees sujected to the sline tretment hd higher / rtio thn the others t the time of hrvest (Fig. 4). In other study, slinity incresed the internl greenish colour of fruits from Clemenules mndrin trees lthough no differences were found on fruits from trees grfted on Crrizo or Cleoptr rootstocks (Grcí-Sánchez et l., 2006). The rootstock, Crrizo or Cleoptr, did not modify the juice, pulp or peel percentges (Fig. 5). However, some studies hve found higher pulp percentge in ornge fruits from Crrizo rootstock thn in those from ) 0.4 ) Externl colour (Hunter /) Internl colour (Hunter /) Slinity ** Rootstock ns Sl. Rootst. ns Slinity ** Rootstock ns Sl. Rootst.** Figure 4. The influence of the slinity tretment nd the rootstock on the evolution of the externl () nd the internl () colour of the fruits two months efore the fruit hrvest. Crrizo 0 mm NCl, open circles; Cleoptr 0 mm NCl, open squre; Crrizo mm NCl, closed circles; Cleoptr mm NCl, closed squre. The sttisticl nlysis refers to hrvested fruits. ns: no significnt. ** P < Seprtion y Duncn s multiple rnge test t the 95% confidence level.

6 S26 J. M. Nvrro et l. / Spn J Agric Res (20) 8(S2), S21-S29 ) Juice (%) ) Pulp (%) c) Peel (%) Slinity ns Rootstock ns Sl. Rootst. ns Slinity * Rootstock ns Sl. Rootst. ns Slinity * Rootstock ns Sl. Rootst. ns Figure 5. The influence of the slinity tretment nd the rootstock on the evolution of the juice (), pulp () nd peel (c) percentges of the fruits two months efore the fruit hrvest. Crrizo 0 mm NCl, open circles; Cleoptr 0 mm NCl, open squre; Crrizo mm NCl, closed circles; Cleoptr mm NCl, closed squre. The sttisticl nlysis refers to hrvested fruits. ns: no significnt. * P < Cleoptr (Forner-Giner et l., 2003; Pérez-Zmor, 2004). Also, for fruits from Crrizo, higher juice percentge nd lower peel percentge thn for fruits from Cleoptr hve een found (Grcí-Sánchez et l., 2003, 2006). Before the hrvest, the juice percentge of fruits from Crrizo irrigted with sline wter ws significntly lower thn in control fruits (Fig. 5), proly due to the lower wter content of these fruits reltive to the control (Fig. 1). However, t the hrvest time, slinity did not modify significntly the juice percentge of these fruits (Fig. 5). As ws oserved for the wter content, fruits from Cleoptr trees suject to slinity did not show differences in the juice percentge with respect to control fruits (Fig. 5). Slinity ppliction did not produce cler responses of the pulp percentge during the experiment; however, t the hrvest time, fruits from trees irrigted with sline wter hd lower pulp percentge (Fig. 5). By contrst, t the end of the experimentl period, the peel percentge ws incresed significntly for fruits of trees irrigted with slinity (Fig. 5c). Similr results hve een found t the hrvest time in Clemenules mndrin fruits of trees irrigted with sline wter (Grcí-Sánchez, 2006). However, other studies hve found higher juice percentge nd lower peel percentge in fruits of vrieties Nvelin nd Clementin de Nules due to slinity (Primo- Millo et l., 2000). One of the most-importnt qulity vriles of citrus juice is the TSS (sugrs nd citric cid eing the most undnt compounds), which plys n importnt role in determining the tste of citrus fruits. From the end of phse II nd throughout phse III of fruit growth, TSS incresed (Fig. 6). Rootstocks my influence the TSS through the degree of dilution, since invigorting rootstocks re etter extrctors of soil wter (Cstle nd Krezdorn, 1977). Since Crrizo is more-invigorting rootstock thn Cleoptr, the wter percentge of control fruits ws higher thn in control fruits from Cleoptr nd the dilution effect ws higher, resulting in lower TSS vlues through the experiment (Fig. 6). Slinity significntly incresed TSS during the experiment, proly due to concentrtion effect since these fruits hd lower wter content (Fig. 1). It is lso possile tht de novo synthesis of sugrs occurred, to chieve osmotic djustment in the fruit, since TSS incresed in fruits from Cleoptr due to slinity ut their wter content ws similr to tht of control fruits (Fig. 1). With similr slinity levels, Grcí-Sánchez et l. (2006) only found n increse of TSS in trees on Crrizo relted with the reduction in juice percentge nd possile osmotic djustment. The TA of the citrus juice is lso n importnt qulity fctor nd it is determinnt for estlishing the optiml hrvest time (Hrding et l., 19). The totl cids in fruits increse in the first stges of mturtion, ut lter remin constnt. As juice percentge increses, cidity decreses with mturtion due to dilution effect. Two months efore the hrvest, fruits from the sline tretment showed cidity levels higher thn

7 Slinity nd mturtion of mndrin fruits S27 ) ) c) TSS TA MI Slinity *** Rootstock ns Sl. Rootst. * Slinity *** Rootstock ns Sl. Rootst. ns Slinity *** Rootstock ns Sl. Rootst. ns Figure 6. The influence of the slinity tretment nd the rootstock on the evolution of the totl solule solids, TSS, (), titrtle cidity, TA, () nd mturity index, MI, (c) of the juice fruit two months efore the fruit hrvest. Crrizo 0 mm NCl, open circles; Cleoptr 0 mm NCl, open squre; Crrizo mm NCl, closed circles; Cleoptr mm NCl, closed squre. The sttisticl nlysis refers to hrvested fruits. ns: no significnt. * P <0.05. *** P < Seprtion y Duncn s multiple rnge test t the 95% confidence level. those of control fruits (Fig. 6). Although these differences ecme less s fruits ripened, t the hrvest time the cidity of fruits from the sline tretment ws still higher (y 28%) thn in control fruits. No differences were found etween rootstocks. Similr to TSS, the increse of the cidity due to slinity could hve een due to concentrtion effect, since these fruits hd lower c wter content, ut lso to de novo synthesis of orgnic cids in the osmotic-djustment process tht occurred in response to slinity (Grcí-Sánchez et l., 2002). The increse of TSS nd the cidity of the fruits with slinity hs een oserved lso y Dserg et l. (1991), in Shmouti ornge, y Cerdá et l. (1986) nd Nieves et l. (1991), with lemon Vern on Cleoptr rootstock, nd y Bielori et l. (1978), for Mrsh grpefruit grfted on sour ornge. However, other uthors hve found n increse of TSS ut decrese in the cidity due to slinity (Primo-Millo et l., 2000; Grcí- Sánchez et l., 2003). In the most importnt citrus-growing res, the lnce etween the TSS nd the sourness produced y cidity is sure, useful nd relile method for evluting fruit qulity nd for determining the fruit mturtion process, nd it is lso the est criterion in correlting fruit qulity with consumer cceptnce (Hrding nd Fisher, 1945; Erickson, 1968; Dvies nd Alrigo, 1994). The stndrd suitle for erly hrvesting is n 8:1 rtio, ut most people prefer sweeter-tsting mndrin; plesnt tste is chieved when this rtio is greter thn. In this experiment, fruits were hrvested t the sme time, so the MI shows the stte of the mturtion process of the fruit in ech tretment. Unlike other studies (Cones, 1999; Wgner et l., 2002; Forner- Giner et l., 2003; Grcí-Sánchez et l., 2003, 2006), nd s we hve previously found (Nvrro et l., 20), no differences were found in MI etween the two rootstocks (Fig. 6). Slinity decresed the MI of fruits y 16% with respect to control fruits, since the increse of the cidity due to slinity ws higher thn tht of the TSS (Fig. 6). Frncois nd Clrk (1980) lso found dely in the mturtion of fruits grown under sline conditions. However, in previous studies, similr increses of TSS nd cidity due to slinity hve een found, resulting in MI vlues similr to those of control fruits (Metochis, 1989; Dserg et l., 1991; Grcí- Sánchez et l., 2003), nd other uthors hve even oserved n increse in the MI with slinity (Primo-Millo et l., 2000; Moring nd Sykes, 2001; Grcí-Sánchez et l., 2006). Although the effect of slinity on the qulity of citrus fruits hs een evluted in severl studies, conflicting results frequently cn e found ecuse of the multiple influences usully present. First, different levels of slinity re used in these studies, nd they re usully pplied during different periods of time. Second, the chrcteristics of the fruits vry enormously in different citrus vrieties, even mong cultivrs. Fruit qulity is

8 S28 J. M. Nvrro et l. / Spn J Agric Res (20) 8(S2), S21-S29 lso influenced y the rootstock; inherent rootstock differences ffecting plnt wter reltions re ssocited with differentil sugr ccumultion of citrus fruits, which is proposed s primry cuse of differences in qulity mong citrus rootstocks (Brry et l., 2004). Moreover, the responses of citrus to slinity could e complex since they depend not only on the rootstock nd the vriety ut lso on the rootstockscion interctions. Even for the sme rootstock-scion comintion, compring field performnce under sline conditions is difficult ecuse of the enormous potentil for interctions with other environmentl fctors (soil chrcteristics, climtic conditions, minerl nutrition, gromngement techniques, plnt ge, size of the root system, etc.) tht could ffect the plnt response to slinity nd hence fruit qulity. Although we could not find studies with similr slinity levels, the sme rootstock-scion comintion nd the sme experimentl conditions, such studies help us to drw generl conclusions for etter understnding of the mechnisms involved in plnt responses to slinity. Conclusions Irrigtion with mm NCl ffected the fruit yield nd qulity of Clemenules mndrin, prticulrly for fruit from trees grfted on Crrizo where the fruit wter content, nd therefore juice percentge, ws reduced. Although slinity produced importnt differences in most of the vriles of fruit qulity during the mturtion process, these decresed until the fruit hrvest. The fruit colour indicted n pprent dvnce of fruit mturtion with the sline tretment; however, the mturity index showed tht the high cidity of these fruits delyed their mturtion with respect to control fruits. Acknowledgements The uthors pprecite the technicl ssistnce of Enrique Bllester nd thnk Dr. Dvid Wlker for correction of the English. This work ws supported y CICYT (AGL C04-04). References ALLEN R.G., PEREIRA L.S., RAES D., SMITH M., Crop evpotrnspirtion-guidelines for computing crop wter requirements. FAO-Irrigtion nd Dringe, pper 56. Rome, Itly. AMORÓS M., Drip irrigtion in citrus trees. Agroguís-Mundiprens, Mdrid. 137 pp. [In Spnish]. BARRY G.H., CASTLE W.S., DAVIS F.S., Rootstocks nd plnt wter reltions ffect sugr ccumultion of citrus fruit vi osmotic djustment. J Amer Soc Hort Sci 129, BIELORAI H., SHALHEVET J., LEVY Y., Grpefruit response to vrile slinity in irrigtion wter nd soil. Irrig Sci 1, BOMAN B.J., Effects of slinity on Vlenci ornge in humid climte. Proc Intl Soc Citricult Vol II, pp CASTLE W.S., Rootstock s fruit qulity fctor in citrus nd deciduous fruit crops. NZJ Crop Hort Sci 23, CASTLE W.S., KREZDORN A.H., Soil wter use nd pprent root efficiencies of citrus trees on four rootstocks. J Amer Soc Hort Sci 2, 3-6. CASTLE W.S., TUCKER D.P.H., KREZDORN A.H., YOUTSEY C.O., Rootstocks for Florid citrus, 2 nd ed. Florid Coop Ext Serv Pul. SP-42. CERDÁ A., CARO M., FERNÁNDEZ F.G., GUILLÉN M.G., Effect of irrigtion wter qulity on Vern lemon response nd soil slinity. Agrochimic, CONESA A., Florción, fructificción, crecimiento y mdurción de los pomelos (Citrus prdisi mcf.) Str Ruy y Río Red. Tesis doctorl. Universidd Politécnic de Mdrid. 458 pp. [In Spnish]. DASBERG S., BIELORAI H., HAIMOWITZ A., ERNER Y., The effect of sline irrigtion wter on Shmouti ornge trees. Irrig Sci 12, DAVIES F.S., ALBRIGO L.G., Citrus. C Int, Wllingford, UK. 254 pp. DOMINGO R., RUIZ-SÁNCHEZ M.C., SÁNCHEZ- BLANCO M.J., TORRECILLAS A., Wter reltions, growth nd yield of Fino lemon trees under regulted deficit irrigtion. Irrig Sci 16, ERICKSON L.C., The generl physiology of citrus. In: The citrus industry II: Physiology, genetics nd reproduction (Reuther W., Btchelor L.D., Weer H.J., eds). University of Cliforni. pp FORNER-GINER M.A., ALCAIDE A., PRIMO-MILLO E., FORNER J.B., Performnce of Nvelin ornge on 14 rootstocks in Northern Vlenci (Spin). Scienti Hortic 98, FRANCOIS L.E., CLARK R.A., Slinity effects on yield nd fruit qulity of Vlenci ornge. J Amer Soc Hort Sci 5, GARCÍA-SÁNCHEZ F., CARVAJAL M., PORRAS I., BOTÍA P., MARTÍNEZ V., Effects of slinity nd rte of irrigtion on yield, fruit qulity nd minerl composition of Fino 49 lemon. Eur J Agron 19, GARCÍA-SÁNCHEZ F., CARVAJAL M., PORRAS I., MARTÍNEZ V., Effects of slinity nd rte of irrigtion on yield, fruit qulity nd minerl composition of Fino 49 lemon. Eur J Agron 19,

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