Rootstock Effects on Deficit-Irrigted Winegrpes in Dry Climte: Vigor, Yield Formtion, nd Fruit Ripening Mrkus Keller, 1 * Lynn J. Mills, 2 nd Jmes F. Hrertson 3 Astrct: A rootstock field tril ws conducted in the Ykim Vlley, southestern Wshington, with three Vitis vinifer cultivrs (Merlot, Syrh, Chrdonny). Vines were grown on their own roots or field-grfted to the rootstocks, 99R,,,, nd n unnmed rootstock from Cornell University (here termed ) tht is likely siling or seedling of 101-14 Mgt. Repeted scion dieck due to cold injury to 99R led us to ndon this rootstock. Vine phenology, vigor, wter sttus, yield formtion, nd fruit ripening nd composition were evluted during three yers eginning in the vineyrd s ninth yer. Own-rooted Merlot nd Chrdonny grew more shoots thn grfted vines, nd nd tended to reduce pruning weights. However, ws the rootstock ssocited with the highest pruning weights in Syrh nd the lowest in Chrdonny. Rootstocks usully did not impct vine phenology, fruit set, nd plnt wter sttus, lthough there ws trend for stem wter potentil to e highest with nd lowest with. The rootstock effect on yield formtion depended on the scion cultivr, nd vritions in different yield components often cncelled out ech other, ut (Merlot nd Syrh), (Merlot nd Chrdonny), nd own roots (Chrdonny) were often ssocited with high yields. Nevertheless, the rootstocks hd only minor effects on fruit ripening nd did not consistently lter solule solids, TA, K +, or nthocynin pigments, ut the ph ws higher in fruit from own-rooted vines compred with grfted Merlot nd Chrdonny. Overll, scion effects nd differences due to yerly climte vrition fr outweighed ny differences due to rootstock. Key words: cultivr, fruit composition, fruit set, grpe erry, growth, rootstock, vigor, Vitis vinifer, yield components Crosses of diverse North Americn Vitis species re used s rootstocks in the mjority of vineyrds throughout the world s the sole fesile mens to prevent vineyrd decline due to infesttion of susceptile Europen winegrpes (Vitis vinifer L.) y phylloxer (Dktulosphir vitifolie Fitch). Rootstocks re lso used for their resistnce to or tolernce of nemtodes, dverse soil conditions such s drought, wterlogging, high or low ph, or slinity, nd their ility to influence vine vigor nd fruit ripening (Currle et l. 1983, Pongrácz 1983, Glet 1998, Whiting 2004). Although the compounds responsile for fruit composition re mostly determined y the genotype of the scion (e.g., Gholmi et l. 1995), rootstocks my lter fruit composition indirectly y influencing scion vigor, cnopy configurtion, yield formtion, nd nutrient uptke (Schumnn 1974, Ruhl et l. 1988, Keller et l. 2001, 2001). 1 Professor of Viticulture, 2 Reserch Technology Supervisor, Deprtment of Horticulture nd Lndscpe Architecture, nd 3 Associte Professor of Enology, School of Food Science, Irrigted Agriculture Reserch nd Extension Center, Wshington Stte University, 24106 N. Bunn Rod, Prosser, WA 99350. *Corresponding uthor (emil: mkeller@wsu.edu; fx: 509 786-9370) Acknowledgments: This work ws funded y WSU s Agriculturl Reserch Center, project WNP00673, nd y the Wshington Wine Advisory Committee progrm. Plnt mteril ws donted y Ste. Michelle Wine Esttes nd Inlnd Desert Nursery. Trellis mterils were donted y Quiedn Compny. The uthors thnk R.L. Wmple for initition of the project nd A. Kwkmi, C. Longori, M. Mireles, nd E. Hrwood for technicl ssistnce. Mnuscript sumitted Aug 2011, revised Oct 2011, ccepted Oct 2011 Copyright 2012 y the Americn Society for Enology nd Viticulture. All rights reserved. doi: 10.5344/jev.2011.11078 Despite the presence of phylloxer in the region nd unlike most of the world s grpegrowing res, the vst mjority of vineyrds in estern Wshington Stte re plnted to vines on their own roots. Vineyrds in this rid region (<300 mm nnul precipittion) re typiclly drip-irrigted using deficitirrigtion strtegies, which re used s tool to control cnopy development nd fruit ripening (Wmple nd Smithymn 2000, Keller et l. ). The min reson for growers reluctnce to dopt rootstocks s culturl prctice is the periodic occurrence of very cold winter tempertures leding to cold injury in grpevines. This is of prticulr economic concern for grfted vines (Folwell et l. 2001), which cnnot simply e retrined from suckers following lethl cold injury to the trunk. Although the ility of Wshington s wine industry to remin competitive is dependent upon the consistent production of high-qulity fruit to mke high-qulity wines, there is no locl experience with the performnce of grfted vines. This lck of fmilirity my leve the industry vulnerle to the indvertent spred of phylloxer, however unlikely such scenrio my seem. To ddress this issue, tsk force ws ssemled in 1992 tht recommended tht Wshington Stte University egin reserch progrm to evlute rootstock dptility to nd performnce under locl climtic nd edphic conditions. The rootstocks V. erlndieri V. ripri Teleki (), V. erlndieri V. rupestris 99 Richter (99R), 140 Ruggeri (), 1103 Pulsen (), V. ripri V. rupestris 3309 Couderc (), nd n unnmed rootstock selection from Cornell University were chosen for evlution. A rootstock field tril ws plnted in 1999, nd evlution of scion performnce egn in 2002. In ddition to the six rootstocks, the three V. vinifer cultivrs tht were used s scions (Merlot, Syrh, Chrdonny) were lso plnted on their 29
30 Keller et l. own roots to permit comprison of vines grfted to rootstocks with own-rooted vines tht remin the industry stndrd. The purpose here is to descrie rootstock effects nd scion rootstock interctions on scion growth, yield formtion, sourcesink reltions, nd fruit ripening under conditions of deficit irrigtion. A compnion study evluted rootstock effects on fruit nd wine composition. The findings of tht study re reported in seprte puliction (Hrertson nd Keller 2012). Mterils nd Methods Vineyrd site, plnt mteril, nd mngement. The experiment ws conducted in vineyrd t the Irrigted Agriculture Reserch nd Extension Center ner Prosser, WA (46 17 40 N; 119 44 37 W; elevtion 365 m), from through. Vines were plnted with 1.83 m etween vines in north-south-oriented rows spced 2.74 m prt on 2% south-fcing slope. The soil is well-drined, uniformly deep (>1 m) Shno silt lom, ph 8.0, with 0.25% orgnic mtter nd n estimted soil wter content (θ v ) of ~25% (v/v) t field cpcity nd ~8% t permnent wilting point (vineyrd 4 in Dvenport et l. ). Merlot, Syrh, nd Chrdonny were evluted on their own roots (OR) or grfted to, 99R,,,, nd n unnmed rootstock received from Cornell University. Rootstocks were propgted y septic shoot-tip culture to eliminte crown gll cteri (Agrocterium vitis), plnted in n increse lock in 1998, nd their identity ws confirmed y DNA typing (Foundtion Plnt Services, UC Dvis, CA). Although the selection from Cornell University ws initilly identified s V. rupestris V. ripri 101-14 Millrdet nd de Grsset (101-14 Mgt), susequent evlution reveled tht it ws not 101-14 Mgt nor ny other commercilly ville rootstock, ut likely siling or seedling of 101-14 Mgt (herefter termed ; P. Cousins nd M.A. Wlker, personl communiction, 2010). Rooted dormnt cuttings were plnted in 1999 nd grfted with certified nursery mteril y chip-udding in 2002. Cold injury due to unsesonly low tempertures in lte Octoer of oth 2002 nd 2003 necessitted regrfting of mny vines in 2003 nd 2004 (Keller et l. ). The vines were trined to two trunks nd ilterl cordons t height of 95 cm nd winter-pruned to two-ud spurs, leving ~25 uds (excluding sl uds) per vine. Shoots were loosely positioned etween two pir of folige wires plced 35 cm (25 cm prt) nd 70 cm (5 cm prt) ove the cordon. No shoot thinning, hedging, or other cnopy mngement prctices were pplied to permit full expression of potentil rootstock effects. The vineyrd ws drip-irrigted using pressure-compensted emitters with flow rte of 2 L/hr, spced 90 cm prt. Irrigtion ws pplied if necessry etween udrek nd loom to void plnt wter stress, then wter ws withheld through mid-july to chieve control of shoot growth, fter which irrigtion ws pplied pproximtely once weekly through summer nd less frequently during the cooler ripening period. The initil gol for the fruit set to verison period ws to mintin trget θ v 11% (verged over the top 90 cm, for mesurement see elow) for Chrdonny nd Merlot nd 10% for Syrh ecuse of the more vigorous shoot growth of the ltter. Given the very low vigor t this site, the trget θ v ws incresed to 11 12% in nd to 13 14% in. The mount of irrigtion wter (IW in mm) to e pplied for ech irrigtion set ws clculted from mesured θ v (converted to mm), rinfll (RF), nd crop evpotrnspirtion (ET c ): IW = trget θ v mesured θ v RF + ET c. In ddition, ET c = 0.8 K c ET 0, where K c ws the pulished V. vinifer crop coefficient (Evns et l. 1993) for pproprite cumultive growing degree dys (GDD, see elow) nd ET 0 ws the pn (grss) evpotrnspirtion for the preceding irrigtion intervl. Following irrigtion ner verison nd during erly ripening, the soil ws gin permitted to dry down to encourge cold cclimtion. After hrvest, irrigtion ws pplied to replenish θ v 18% to minimize cold injury to roots in winter. Nitrogen fertilizer (NH 4 NO 3 (NH 2 ) 2 CO) ws pplied nnully t rte of ~20 kg N/h y fertigtion; the rte ws split etween the six-lef nd loom stges. Becuse some vines showed symptoms of potssium deficiency in, potssium fertilizer (K 2 SO 4 2MgSO 4 ) ws shnked ~10 cm into the soil on oth sides of ech vine row fter hrvest of nd t rte of ~170 kg K/h. Vineyrd floor mngement consisted of mowing permnent cover crop nd 120 cm under-vine hericide strip. Mesurements. Meteorologicl conditions were monitored using dily rw dt derived from Wshington Stte University AgWetherNet wether sttion tht hs een in opertion since 1989 nd is locted t the sme elevtion <1 km to the est of the tril site. Growing-seson het units were estimted s GDD > 10 C ccumulted from 1 Apr through 31 Oct, using dily men tempertures clculted from dily mximum (T mx ) nd minimum tempertures (T min ). Neutron proes (503 DR Hydroproe; CPN Interntionl, Concord, CA) were used to monitor θ v. One ( nd ) or two () PVC proe-ccess tues were instlled in ech scion/ rootstock comintion to soil depth of 1 m eneth the drip line nd equidistnt etween drip emitters. In ddition, stem wter potentil (i.e., petiole xylem pressure, Ψ x ) ws mesured using pressure chmer (PMS Instrument Co., Alny, OR) on t lest four leves per tretment replicte. Fully expnded, sun-exposed leves were mesured fter they hd een enclosed in luminum-coted plstic gs for >30 min etween 11:00 nd 15:00 LST. Mesurements were conducted four times efore nd once fter verison in, four times ech efore nd fter verison in, nd weekly from fruit set through hrvest in. Vine phenology ws monitored t lest weekly. Flowers per cluster nd percent fruit set were estimted y counting scised flower cps collected in guze gs (1 mm perfortions) nd counting the erries of the sme clusters (Keller et l. 2010). Averge flower size for ech cluster ws estimted y drying (60 C) nd weighing the collected flower cps, ssuming tht cp weight is proportionl to flower weight nd, hence, size (Keller et l. 2010). Yield, clusters per vine, nd men erry weight were determined t hrvest nd used to estimte clusters per shoot nd erries per cluster. Pruning weights were recorded during winter pruning, nd cnes were counted t the sme time.
Rootstock Effects on Vine Performnce 31 Fruit ripening ws ssessed y iweekly smpling eginning during the lg phse of erry growth. Five erries were plucked from ech of five clusters per replicte, lterntely from the top, middle, nd ottom of ech cluster, nd kept in zip-lock g on ice. At hrvest, which occurred on the sme dy for ll rootstocks within scion cultivr, 100 erries were collected per replicte. Berry smples were weighed nd nlyzed the following dy for totl solule solids (TSS), titrtle cidity (TA), ph, nd nthocynin color (Hrertson nd Keller 2012). Juice potssium concentrtion ([K + ]) ws mesured in nd hrvest smples s descried y Hrertson nd Hrwood (). Additionl fruit composition dt nd winemking procedures nd results re reported in compnion pper (Hrertson nd Keller 2012). Experimentl design nd dt nlysis. The experiment ws designed s split-plot with ech of the three cultivrs rndomly ssigned to oth of two djcent 15-row locks nd the seven rootstocks (one own-rooted nd six grfted tretments) ssigned to five suplots within ech cultivr min plot. Ech cultivr plot consisted of five rows (60 vines/row), nd ech rootstock ws replicted once (7 vines/rootstock) in ech row. There were five or six own-rooted uffer vines t either end of the row nd five uffer rows on either side of the experimentl unit. All mesurements were tken on three interior vines (dt vines), flnked y two uffer vines of the sme rootstock on either side of ech of the 10 scion/ rootstock replictes. Vegettive nd yield component dt were collected seprtely for ech dt vine. Fruit set ws estimted on oth clusters of one two-cluster shoot on one vine of five scion/rootstock replictes. Fruit composition dt were collected s composite smples from the dt vines of ech replicte. All dt were nlyzed using Sttistic (version 10; Stt- Soft, Tuls, OK). Results were first nlyzed s split-splitplot design using four-wy (yer lock cultivr rootstock) nlysis of vrince (ANOVA) nd F-test. Becuse the lock effect ws lmost never significnt nd cultivr rootstock interctions were lmost lwys significnt, dt were next sujected to three-wy (yer cultivr rootstock) ANOVA. Three-wy interctions were lmost never significnt, ut yer nd cultivr effects nd yer cultivr interctions were lmost lwys significnt nd often filed Levene s test due to differences in vrince mong yers. Therefore, dt were lso nlyzed y two-wy ANOVA using the generl liner model procedure. This nlysis ws performed y cultivr (yer rootstock) to test for consistency of rootstock effects within cultivrs over time nd y yer (cultivr rootstock) to test for consistency of rootstock effects cross cultivrs. Duncn s new multiple rnge test ws used for posthoc comprison of significnt tretment mens, nd orthogonl contrsts were used to compre own-rooted vines with grfted vines for ech cultivr. The θ v, Ψ x, erry weight, nd fruit composition dt were nlyzed with repeted mesures design. Individul ph vlues were converted to [H + ] for sttisticl nlysis, nd the reported mens were reclculted from mens of [H + ]. Correltion nlysis ws used to compre reltionships etween selected pirs of vriles. Results Wether, soil moisture, nd vine wter sttus. Among the three growing sesons, nd were elow nd ws ove the 22-yer verge in terms of het ccumultion from 1 Apr through 31 Oct (Figure 1). Men T mx / T min etween udrek (phenologicl stges were verged for the three cultivrs) nd loom ws similr mong yers, vrying only from 22.3/7.4 C () to 22.8/7.9 C (). The T mx /T min rnge during loom-fruit set ws more pronounced: 23.1/8.3 C () to 26.8/10.2 C (). The vrition of 29.3/13.5 C () to 30.1/13.0 C () ws gin low etween fruit set nd verison ut significnt from verison to hrvest, rnging from 22.4/9.0 C () to 27.3/10.9 C (). While nd hd similr numers of hot (T mx > 30 C) nd very hot (T mx > 35 C) dys during the growing seson, hd considerly more hot nd very hot dys, most of which occurred etween fruit set nd verison (Tle 1). hd the most cool (T mx < 15 C) nd very cool (T mx < 10 C) dys in spring, nd hd severl very cool dys in fll. The first fll frost occurred etween 1 d efore () nd 16 d fter () the hrvest of Syrh, which ws lwys the lst cultivr to e hrvested. Precipittion ws elow verge in ll three yers, nd there ws very little rinfll during the growing seson (Tle 1). At udrek, θ v of the top 90 cm of soil vried from considerly elow (: 17.5% v/v; : 18.9%) to slightly elow (: 22.6%) field cpcity. Becuse of miniml rinfll, the susequent θ v pttern mostly reflected the sesonl irrigtion strtegy. In the soil egn to dry down immeditely fter udrek, wheres in nd more frequent irrigtion kept θ v high through fruit set (Figure 2). In ll yers, θ v reched temporry minimum efore verison, ut θ v ws lower (p < 0.001) throughout the growing seson thn in the other two yers except for strong temporry increse due to irrigtion t verison. Ech yer, nd s intended y the irrigtion strtegy, the soil under Syrh ws usully 1% (v/v) drier thn tht under Merlot nd Chrdonny (p < 0.05). Across the three scion cultivrs, ws Figure 1 Growing degree dy ccumultion (se 10 C) in Prosser, WA, from 1 Apr to 31 Oct through.
32 Keller et l. the rootstock tht ws ssocited with the lowest θ v, which ws on verge ~1.2% (v/v) lower thn with other rootstocks nd own-rooted vines (p < 0.01, dt not shown). The only other significnt rootstock effect ws the trend in towrd slightly elevted θ v with (p < 0.01). Ech yer, however, the sptil vrition in θ v due to vrying soil properties cross the vineyrd lock ws usully greter thn tht due to either scion or rootstock cultivr. In nd, ut not in, there were significnt positive correltions etween θ v nd Ψ x for ll three scion cultivrs; the strength of the reltionship vried mong cultivrs s well s etween yers (0.36 < r < 0.82, p < 0.05). When the Ψ x dt were verged for the pre- or postverison erry development phses, there were few nd inconsistent differences mong scion cultivrs (Tle 2) nd none mong rootstocks (dt not shown). Sesonl trends nd men vlues of Ψ x were rther similr mong scion cultivrs in, ut Syrh mintined somewht higher Ψ x fter verison in thn did the other cultivrs (Tle 2). In Chrdonny sustined the highest Ψ x fter verison. Evluting individul mesurement dtes uncovered few significnt ut smll differences mong rootstocks (dt not shown). All three cultivrs mintined the highest middy Ψ x on throughout most of the growing seson (p < 0.05). In, vines (especilly Syrh) grfted to hd lower Ψ x compred with other rootstocks (p < 0.05). In, (long with ) gin led to the highest Ψ x, while nd were ssocited with the lowest Ψ x (p < 0.001). Own-rooted vines did not differ from grfted vines in ny cultivr or yer. Vine growth. One of the rootstocks, 99R, ws eliminted from the evlution ecuse oth the rootstock itself nd the scions grfted to it often died ck during the winter Tle 2 Effect of scion cultivr on verge middy stem wter potentil (Ψ x ) during fruit ripening of field-grown grpevines in the Ykim Vlley, WA (ll se 0.05 MP). Scion Merlot Syrh Chrdonny Signf Ψ x (MP) -0.83-0.71-0.77 0.070-1.18-0.99-1.17 0.012-1.26-1.30-1.01 Significnce (p vlue) of cultivr effect. Preverison mens were similr for ll cultivrs (verge -0.81 MP in ; -0.84 MP in ; -1.01 MP in ). Mens within columns followed y different letters differ significntly t p < 0.05 y Duncn s new multiple rnge test. Tle 1 Meteorologicl dt from the Wshington Stte University AgWetherNet Roz wether sttion ner Prosser, WA (<1 km est of vineyrd site). Yer GDD ( C) Sesonl temperture (d) Precipittion (mm) >30 C PV/RP >35 C PV/RP <15 C S/F <10 C S/F Annul Sesonl 1989 2010 1314 1333 1481 1409 26/8 30/3 33/14 38 1/0 5/0 11/2 7 Cumultive growing degree dys (>10 C) nd rinfll from 1 Apr to 31 Oct. Numer of dys from 1 Apr to 31 Oct with mximum tempertures greter or lower thn four threshold tempertures (PV: preverison/rp: ripening; S: spring/f: fll). 16/19 23/13 14/12 13/11 0/0 6/0 2/6 1/2 152 117 135 227 70 45 64 111 Figure 2 Influence of growing seson nd scion cultivr on the volumetric soil wter content in the top 90 cm (mens ± se) of deficit-irrigted rootstock tril lock in Prosser, WA, in (n = 5), (n = 5), nd (n = 10; BB: udrek, B: loom, V: verison, H: hrvest).
Rootstock Effects on Vine Performnce 33 following grfting. Those vines tht survived the first two yers fter grfting hve hd no further prolems with winter survivl, proly ecuse once estlished, the woody rootstocks nd grfts no longer suffered from the lte mturtion tht chrcterized their green shoots. Among the remining rootstocks (including own-rooted vines) there ws no consistent effect on scion phenology in ny cultivr (dt not shown). However, own-rooted Merlot nd Chrdonny hd greter cpcity for growth thn did grfted vines. Across the three yers nd despite efforts to prune to similr ud numers, these cultivrs grew on verge 52% more shoots (21/m) on their own roots thn when they were grfted (14/m; Tle 3). Merlot nd Chrdonny grfted to nd usully grew intermedite shoot numers. These differences decresed from to s the vines mtured. No such rootstock effect ws oserved with Syrh s the grfting prtner; ll comintions grew ~15 shoots/m of cnopy (Tle 3). Tle 3 Effect of rootstock on mesures of vine vigor nd lnce of three scion cultivrs in the Ykim Vlley, WA, over three yers. Merlot Syrh Chrdonny Signf S R Y S Y R Pruning wt (g/m) 246 254 177 184 230 253 218 236 219 301 c 351 306 c 246 c 393 306 c 288 322 335 442 390 211 c 233 c 195 c 326 245 321 340 0.053 0.017 Cne no. (cnes/m) 20 16 13 c 14 c 15 c 16 19 13 14 16 17 14 16 17 16 18 15 15 23 17 13 d 15 cd 14 d 16 c 22 13 14 0.301 Cne wt (g) 12.8 c 16.8 13.7 c 13.9 c 15.7 15.9 11.8 c 17.6 15.0 19.9 19.8 19.3 15.1 c 21.4 18.0 c 17.2 20.1 19.4 20.3 22.6 16.1 cd 15.3 cd 14.0 d 19.1 c 11.1 20.7 21.9 0.097 Yield: pruning wt 10.1 d 13.0 c 15.0 12.4 cd 16.0 10.4 cd 7.0 c 17.2 13.2 7.3 d 8.9 cd 14.2 11.0 c 14.5 11.3 c 6.7 c 15.5 10.4 7.3 c 9.0 c 16.9 10.7 16.0 9.2 c 8.9 12.9 11.1 0.195 0.031 Significnce (p vlue) of scion (S) rootstock (R), yer (Y) S, nd Y R interctions. Rootstock nd yer mens within columns followed y different letters differ significntly t p < 0.05 y Duncn s new multiple rnge test. Shoot numers vried more thn 10-fold ut were strongly correlted etween yers in ll scion/rootstock comintions (0.77 < r < 0.81, p < 0.001), indicting tht the sptil vrition within this vineyrd ws dominnt over the temporl vrition. While shoot numer my e tken s mesure of vine cpcity, verge cne weight t pruning is etter indictor of shoot vigor. These two vriles re usully inversely relted (i.e., vines tht grow more shoots grow less vigorously), ut in this study there ws no consistent ssocition etween shoot numer nd cne weight. Cne weights were lowest fter the growing seson nd similr in the other two yers (Tle 3). Syrh hd hevier cnes thn Merlot nd Chrdonny in, nd Merlot hd lighter cnes thn the other cultivrs in nd (p < 0.001). Merlot produced hevier cnes on,, nd thn on the other rootstocks or own roots, wheres led to lower cne weights compred with other rootstocks in Syrh. Chrdonny cnes were heviest in own-rooted vines,, nd. In ll three cultivrs, the vrition in pruning weight ws somewht more closely ssocited with differences in cne weight (0.60 < r < 0.86, p < 0.001) thn with differences in cne numer (0.46 < r < 0.69, p < 0.001). In ll scion cultivrs nd rootstocks, pruning weight ws positively correlted with the previous winter s pruning weight. The contriution of the vrition in pruning weight in one yer to tht in the following yer incresed from to : r = 0.50 0.70 for Merlot; r = 0.55 0.83 for Syrh; nd r = 0.54 0.87 for Chrdonny (ll p < 0.001). These results show tht lrger vines remined lrger over time nd tht within-vineyrd vrition chnged little from yer to yer. Merlot consistently hd the lowest pruning weights, nd Syrh hd the highest pruning weights in ut ws similr to Chrdonny in nd (Tle 3). While Merlot pruning weights did not exceed 0.7 kg/m of cnopy, some Syrh nd Chrdonny vines reched pruning weights of up to 1.6 kg/m. However, the men (± se) pruning weight vried only from 0.22 ± 0.01 to 0.34 ± 0.02 kg/m cross scion cultivrs nd yers. The rootstock effect ws significnt in nd, which resulted in significnt yer rootstock interction (Tle 3). Becuse the scion rootstock interction ws lso significnt, the rootstock effect ws nlyzed seprtely for ech cultivr. In Merlot, nd decresed pruning weights y 27% compred with other rootstocks nd ownrooted vines (Tle 3). Syrh hd the lowest pruning weights when grfted to nd the highest on. Chrdonny pruning weights were 49% lower with,, nd compred with nd own-rooted vines. Yield formtion nd vine lnce. A vine s yield potentil t the eginning of growing seson my e estimted from the numer of clusters per vine (shoots/vine clusters/ shoot) nd the verge numer of flowers per cluster (inflorescence size). Annul vrition dominted the totl vrition in cluster numers. Despite higher shoot numers, there were generlly fewer clusters per vine in thn in nd, with rnge mong mens of 1.6-fold in Merlot, 1.8- fold in Syrh, nd 1.3-fold in Chrdonny (Tle 4). There ws significnt yer rootstock interction cross ut not
34 Keller et l. within scion cultivrs, indicting tht the rootstock effect on cluster numers of ech scion ws reltively consistent over time. Merlot produced fewer clusters when grfted to nd compred with other rootstocks nd own-rooted vines, Syrh ws most productive on, nd Chrdonny produced the fewest clusters on nd the most on its own roots (Tle 4). Merlot hd the fewest flowers per cluster in nd the most in, while inflorescence size vried little from yer to yer in Syrh nd Chrdonny (Tle 5). Chrdonny hd the lrgest flowers, followed y Syrh nd finlly Merlot (p < 0.001). Across scion cultivrs, flowers were 23% smller in thn in nd (Tle 5), nd ws often ssocited with smller flowers compred with other rootstocks nd own-rooted vines (p < 0.01). Wheres there ws no significnt rootstock effect on Merlot nd Chrdonny inflorescence size, Syrh tended to produce more flowers per inflorescence on nd thn on its own roots (p < 0.05). Merlot hd more flowers per Tle 4 Effect of rootstock on yield nd its components of three scion cultivrs in the Ykim Vlley, WA, over three yers. Merlot Syrh Chrdonny Signf S R Y S Y R Yield (kg/vine) 4.50 c c 5.26 4.29 c 4.05 c 5.44 4.65 c 2.70 c 6.24 4.86 3.84 c 5.11 5.15 4.34 c 7.05 4.64 c 3.40 c 6.90 4.41 5.37 5.25 3.83 4.14 4.17 4.35 3.77 4.86 4.92 0.019 Clusters /vine 73 69 59 58 69 67 48 75 72 51 54 54 52 67 55 42 75 47 91 79 65 c 68 c 70 c 73 c 64 77 82 0.012 Cluster wt (g) 57 c 74 66 63 c 75 66 56 c 76 67 70 d 88 85 c 79 cd 97 76 cd 73 86 87 57 65 55 57 54 56 57 58 58 Berries /cluster 57 c 71 61 c 64 66 64 64 67 61 59 d 78 69 c 68 c 76 62 cd 68 66 72 58 58 54 59 52 55 67 49 c 55 0.398 Berry wt (g) 0.98 c 1.06 c 1.10 1.04 c 1.16 1.03 c 0.85 c 1.19 1.11 1.21 c 1.15 c 1.26 1.16 c 1.32 1.24 1.14 c 1.32 1.21 1.01 1.11 1.05 1.04 1.03 1.07 0.85 c 1.20 1.08 0.016 0.015 Significnce (p vlue) of scion (S) rootstock (R), yer (Y) S, nd Y R interctions. Yield in t/h cn e otined y douling the numer in kg/vine. c Rootstock nd yer mens within columns followed y different letters differ significntly t p < 0.05 y Duncn s new multiple rnge test. cluster thn Syrh nd Chrdonny, ut Syrh set more fruit thn did Merlot nd Chrdonny (Tle 5). The percentge fruit set in Merlot nd Syrh ws lowest in nd highest in (p < 0.001), while Chrdonny fruit set vried little from yer to yer. The rootstock did not lter fruit set in Syrh, ut own-rooted Merlot set ~8% more fruit thn did its grfted counterprts (p < 0.05), wheres Chrdonny hd ~9% lower fruit set on thn on other rootstocks or own roots (p < 0.05). In Merlot nd Syrh, the numer of erries per cluster ws not relile indictor of fruit set (r < 0.11, n.s.), ut insted ws more closely ssocited with the numer of flowers per cluster (r > 0.64, p < 0.001). In Chrdonny, oth flower numer (r = 0.43, p < 0.001) nd percentge fruit set (r = 0.48, p < 0.001) contriuted eqully to the vrition in erry numer. Except in own-rooted vines of ll cultivrs, cluster weights vried fr less from yer to yer thn did cluster numers (Tle 4). Becuse of compensting effects of flower numers nd fruit set, the numer of erries per cluster ws much less dependent on sesonl effects thn on scion cultivr nd rootstock, lthough the internnul vrition ws quite pronounced (1.4-fold) in Chrdonny (Tle 4). Chrdonny hd fewer erries per cluster (56 ± 1.2) thn Merlot (64 ± 0.9) nd Syrh (69 ± 1.2). Own-rooted Merlot nd Syrh hd fewer erries per cluster thn grfted vines, while vines on nd typiclly hd the most erries per cluster (Tle 4). The vrition in erry weights ws gin dominted y sesonl effects: erries were smllest in nd lrgest in with men rnge of 1.4-fold in Merlot nd Chrdonny nd 1.2- fold in Syrh (Tle 4). Syrh consistently hd hevier erries thn the other cultivrs (p < 0.001). Merlot nd Syrh gener- Tle 5 Inflorescence nd flower size (estimted from dry weights of collected flower cps) nd fruit set of three scion cultivrs in the Ykim Vlley, WA, over three yers. Merlot Syrh Chrdonny Signf S R S R Y S Y R Flowers /cluster 265 c c 475 358 233 264 245 261 258 0.076 0.270 0.056 Flower size (mg) 0.30 c 0.40 0.37 0.32 c 0.44 0.42 0.56 0.59 0.005 0.479 0.230 Fruit set (%) 38 33 c 43 57 53 61 39 42 0.408 0.580 0.351 0.291 Flower cps not collected for Chrdonny in. Significnce (p vlue) of scion (S) nd rootstock (R) effects nd S R, yer (Y) S, nd Y R interctions. c Yer mens within columns followed y different letters differ significntly t p < 0.05 y Duncn s new multiple rnge test.
Rootstock Effects on Vine Performnce 35 lly produced slightly hevier erries on thn on other rootstocks or on their own roots. Consequently, own-rooted Merlot nd Syrh tended to hve the smllest clusters, nd vines grfted to nd the lrgest (Tle 4). In Merlot, the ltter two rootstocks were lso ssocited with 21% higher yields compred with other rootstocks or own roots, wheres Syrh on produced 61% more crop thn on other rootstocks or own roots. Rootstocks did not influence erry numers nd erry weights on Chrdonny clusters. Nonetheless, yields of own-rooted nd -grfted Chrdonny were 28% higher in comprison with other rootstocks (Tle 4). Across scion cultivrs, own-rooted vines produced lower yields thn grfted vines in ut not in nd. Averge yields in ll three cultivrs nd cross rootstocks were lowest in, ut the nnul vrition ws more pronounced in Merlot (2.3-fold) nd Syrh (2-fold) thn in Chrdonny (1.3-fold). Merlot nd Syrh yields were highest in, while Chrdonny yields were similr in nd. Most of the vrition in the yield:pruning-weight rtio (Y/P) ws due to sesonl effects followed y rootstock effects. The Y/P ws generlly lowest in nd highest in (Tle 3); the men vried 2.5-fold in Merlot, 2.3-fold in Syrh, nd 1.4-fold in Chrdonny. All three scion cultivrs hd higher Y/P on nd thn on other rootstocks (Merlot +35%, Syrh +49%, Chrdonny +81%; p < 0.001), with own-rooted vines consistently t the low end (Tle 3). For ll cultivrs, there were significnt positive correltions etween pruning weight nd cluster numer s well s yield in the following seson, nd these correltions generlly ecme stronger over time (dt not shown). Although yields on n individul vine sis vried from 0 to 34 t/h in Merlot, from 0 to 40 t/h in Syrh, nd from 0 to 25 t/h in Chrdonny, there ws no sign of higher yields leding to lower pruning weights. On the contrry, higher-yielding vines were ssocited with higher pruning weights the following winter: r = 0.67 for Merlot, r = 0.72 for Syrh, nd r = 0.75 for Chrdonny (ll p < 0.001). Thus, lrger vines hd greter yield potentil thn smller vines, nd higher yields did not compromise vine size nd cpcity for the susequent yer. Fruit ripening nd composition. Vrition in fruit ripening ws dominted y scion nd yer effects. Rootstocks contriuted little to this vrition nd to within-vineyrd vrition (dt not shown). Sugrs typiclly ccumulted rpidly during the first 30 to 35 dys of the ripening period, ut ccumultion slowed mrkedly therefter nd effectively cesed 40 dys fter verison in Chrdonny, 40 to 45 dys fter verison in Merlot, nd 45 to 50 dys fter verison in Syrh. The rte of sugr ccumultion (Brix/d) ws positively correlted with the rte of orgnic cid degrdtion (g TA/L/d), ut the degree of this ssocition vried y cultivr: r = 0.58 for Merlot; r = 0.29 for Syrh; r = 0.88 for Chrdonny (ll p < 0.001). The low yields in nd, to lesser extent, the high tempertures in ccelerted sugr nd nthocynin ccumultion nd cid degrdtion compred with in Merlot nd Syrh, ut merely dvnced the onset of ripening in Chrdonny. Although erries of ll cultivrs lso hd higher ph during the initil ripening phse of, ph ws lower during tht period when compred t similr TA or TSS concentrtions (p < 0.001). While TA declined rpidly during the erly ripening phse, the decrese slowed round 16 to 18 Brix nd essentilly cesed t ~20 to 21 Brix, irrespective of cultivr, rootstock, nd yer. Nonetheless, ph consistently continued to increse to t lest 24 to 26 Brix. Over the entire ripening period, correltions etween TSS nd ph (trnsformed to [H + ]) were generlly higher (r > 0.92, p < 0.001) nd less vrile from yer to yer thn were correltions etween TA nd ph (r > 0.84, p < 0.001). Anthocynins in Merlot nd Syrh erries incresed during ripening ut usully reched plteu t 22 to 24 Brix. In Syrh this plteu shifted to 28 Brix in, when nthocynins ccumulted more slowly ut to similr finl level compred with the other yers. With few exceptions there ws no cler rootstock effect on sugr nd nthocynin ccumultion or orgnic cid degrdtion in the fruit (dt not shown). Significnt scion rootstock nd yer rootstock interctions indicted tht rootstock effects were neither consistent mong scion cultivrs nor mong growing sesons within cultivr. In, fruit from Syrh on hd lower TSS nd ph throughout most of ripening compred with other rootstocks nd own roots (p < 0.05) nd egn the ripening phse with higher TA thn own-rooted Syrh (p < 0.01). In, grpes from own-rooted Merlot hd the highest ph throughout ripening, nd the difference incresed over time (p < 0.001). Ripening grpes from own-rooted Syrh hd higher TSS thn did grpes from grfted Syrh (p < 0.001); the former, together with, lso hd the lowest TA (p < 0.05), highest ph (p < 0.01), nd highest nthocynin concentrtions (p < 0.001). Sugr ccumultion nd cid degrdtion in Chrdonny ws fster on its own roots,, nd thn on the other rootstocks ( p < 0.05), nd grpes from own-rooted Chrdonny hd higher ph throughout ripening (p < 0.001). In, ws ssocited with more rpid cid degrdtion thn nd in Syrh, nd nd led to fster cid degrdtion compred with other rootstocks or own roots in Chrdonny (p < 0.05). The ph incresed more slowly in grpes from own-rooted compred with grfted Chrdonny, ut it strted from higher level t verison (p < 0.05). In Merlot, y contrst, the ph ws similr cross rootstocks t verison, ut incresed more rpidly in own-rooted vines (p < 0.001). Berries from Syrh grfted to hd the highest nthocynin concentrtions throughout ripening ( p < 0.01). For the most prt, differences in fruit composition mong rootstocks disppered y hrvest (Tle 6; rootstock dt not shown). However, there ws significnt scion rootstock interction on ph: ech yer fruit from own-rooted Merlot nd Chrdonny hd the highest ph (p < 0.001), ut tht ws not true for Syrh. Merlot grfted to consistently hd the lowest ph (0.2 units elow own-rooted vines) followed y (p < 0.001); lso consistently led to slightly lower ph in Syrh (p < 0.05), ut there were no differences mong rootstocks in grfted Chrdonny. The ph ws lwys positively correlted with [K + ] (0.32 < r < 0.70, p < 0.001 to 0.05) nd often ut not lwys inversely correlted with TA (-0.89 < r < 0.05, p < 0.001 to 0.75). Fruit from Merlot on its
36 Keller et l. own roots hd the lowest TA, while ws consistently ssocited with the highest TA t hrvest (p < 0.001). No significnt differences were found mong rootstocks for ny other fruit composition vrile in ny scion cultivr. The following reltionships prtly reflected the low crop nd ssocited rpid ripening in, ut correltions of similr mgnitude nd direction s those reported cross yers were often found within yers. Across yers there were negtive correltions etween yield nd TSS (Merlot: r = -0.60; Syrh: r = -0.52; Chrdonny: r = -0.26; ll p < 0.001) nd etween yield nd ph (Merlot: r = -0.38; Syrh: r = -0.53; Chrdonny: r = -0.24; ll p < 0.01) ut not TA. Somewht weker negtive correltions were lso found etween Y/P nd TSS for Merlot (r = -0.51, p < 0.001) nd Syrh ( r = -0.48, p < 0.001), ut not for Chrdonny. Still the ph decresed with incresing Y/P in ll cultivrs (Merlot: r = -0.51; Syrh: r = -0.24; Chrdonny: r = -0.42; ll p < 0.01), while [K+] decresed significntly only in Merlot (r = -0.34, p < 0.001) nd Syrh (r = -0.21, p < 0.001). The ph incresed s cnopy density (shoots/m) incresed in Merlot (r = 0.50, p < 0.001) nd Chrdonny (r = 0.39, p < 0.001), ut not in Syrh. This ssocition ws prtly driven y the higher shoot numer (Tle 3) nd higher ph of own-rooted Merlot nd Chrdonny compred with grfted vines. There were positive correltions etween verge postverison (ut not preverison) Ψ x nd TSS (Merlot: r = 0.46; Syrh: r = 0.38; Chrdonny: r = 0.59; ll p < 0.01). Yet TA ws positively correlted with oth preverison Ψ x (Merlot: r = 0.58; Syrh: r = 0.55; Chrdonny: r = 0.59; ll p < 0.001) nd postverison Ψ x (Merlot: r = 0.64; Syrh: r = 0.42; ll p < 0.01; Chrdonny: n.s.). Anthocynins were negtively correlted with oth preverison Ψ x (Merlot: r = -0.51; Syrh: r = -0.46; ll p < 0.001) nd postverison Ψ x (Merlot: r = -0.70; Tle 6 Bsic fruit composition t hrvest of three scion cultivrs in the Ykim Vlley, WA, over three yers. Merlot Syrh Chrdonny Signf S R S R Y S Y R TSS (Brix) 25.2 23.4 c 24.5 26.7 22.1 c 24.5 25.4 23.2 23.5 0.055 0.288 0.698 0.263 TA (g/l) 8.06 6.78 5.89 c 8.33 8.43 6.95 8.47 9.07 8.01 0.083 0.019 0.905 ph 3.61 3.52 3.54 3.54 3.49 c 3.61 3.39 3.27 c 3.35 0.633 K + (g/l) 2.04 1.69 1.58 1.89 1.15 1.25 0.072 0.949 0.204 Significnce (p vlue) of scion (S) nd rootstock (R) effects nd S R, yer (Y) S, nd Y R interctions. Yer mens within columns followed y different letters differ significntly t p < 0.05 y Duncn s new multiple rnge test. Syrh: r = -0.46; ll p < 0.001). In Syrh, ut not in the other cultivrs, fruit [K + ] incresed s Ψ x decresed oth preverison (r = -0.84, p < 0.001) nd postverison (r = -0.76, p < 0.001), which ws coupled to n increse in ph with decresing preverison Ψ x (r = -0.54, p < 0.001) nd postverison Ψ x (r = -0.31, p < 0.05). Yet, none of these ssocitions etween plnt wter sttus nd fruit composition were ltered y grfting or the rootstocks used in this study. Discussion This three-yer tril in deficit-irrigted vineyrd tested the inf luence of six rootstocks, in comprison with ownrooted vines, on wter use, growth, yield formtion, nd fruit ripening of three V. vinifer cultivrs. From n economic perspective, we currently cnnot recommend plnting 99R or other rootstocks with very long vegettive cycles in res with short growing sesons nd cold winters ecuse their lte shoot mturtion ppers to e ssocited with lte cold cclimtion nd hence poor initil grft survivl in winter. Overll, the remining rootstocks induced few, nd often minor, differences in scion performnce. This finding ws true not only for the vrition mong the different rootstocks, ut lso for the vrition introduced y grfting in comprison with own-rooted vines. The vrition of most vriles evluted here ws clerly dominted y nnul climte vrition, sptil differences cross the vineyrd, nd differences mong scion cultivrs. Where rootstock effects were significnt nd consistent from yer to yer, there lso often ws significnt scion rootstock interction, indicting tht scion cultivrs modified the rootstock impct. Bsed on θ v mesurements, ppered to e ssocited with somewht higher soil wter use, ut tht ws not reflected in Ψ x mesurements. The ltter indicted tht vines grfted to tended to mintin slightly higher nd those grfted to slightly lower wter sttus thn other vines. Other studies found no or inconsistent rootstock effects on vine wter sttus (estimted s middy Ψ lef ) in Chrdonny (Stevens et l. ), Syrh (Stevens et l. 2010), or Cernet Suvignon (Nuzzo nd Mtthews 2006, Willims 2010). However, our mesures of vine vigor, such s shoot numer, cne weight, nd pruning weight, suggested tht own-rooted vines were more vigorous thn were grfted vines nd consistently induced low vigor; ws often grouped with own-rooted vines nd with. The >50% higher shoot numer of own-rooted Merlot nd Chrdonny compred with grfted vines ws especilly striking. In contrst, ws ssocited with high vigor in Syrh, intermedite vigor in Merlot, nd low vigor in Chrdonny. However, over the three yers oth pruning weights nd cne weights generlly remined low y pulished stndrds. Optimum pruning weights re thought to e in the rnge of 300 to 600 g/m of cnopy, nd optimum cne weights fll in the rnge of 20 to 40 g (Smrt 1985, Smrt et l. 1990). All three scion cultivrs used here hd yerly verge vlues ner or elow the lower limit of these rnges, nd no rootstock ws ssocited with vlues tht exceeded their upper limit in ny cultivr. In ddition, despite considerle vrition mong
Rootstock Effects on Vine Performnce 37 vines, the verge shoot numer per unit cordon length, mesure of cnopy density, ws close to the optimum of 15 shoots/m. This suggests tht in dry climtes vine vigor is predominntly controlled y wter deficit (nd hence y irrigtion), with rootstocks hving only minor effect. Moreover, the overll direction of this effect ws generlly one of lower vigor compred with own-rooted vines; rootstocks such s nd my decrese oth scion cpcity nd vigor. However, nd led to higher vigor thn did in unirrigted Cernet Suvignon (Nuzzo nd Mtthews 2006). A recent field tril, conducted under similr climtic conditions, uncovered no differences in scion vigor mong irrigted own-rooted Mlec nd Mlec grfted to,,, mong other rootstocks (Di Filippo nd Vil 2011). Of the rootstocks tested in the present study, the viticulturl literture often clssifies s drought tolernt, 99R nd s intermedite to tolernt, s less to poorly tolernt, nd s poorly drought tolernt (e.g., Glet 1998, Whiting 2004). Yet, 99R,, nd were reported to e quite drought tolernt when grfted to nonfruiting Cernet Suvignon nd grown in snd in smll pots (Cronneu 1985). More recently, nd, nd in some cses, were found to tolerte wter deficit eqully well when grfted to mture, fruit-ering Chrdonny (Stevens et l. ), Syrh (Stevens et l. 2010), or Cernet Suvignon (Willims 2010). With the exception of the Mlec tril mentioned ove, none of these studies included own-rooted vines for comprison. Becuse of its geogrphic origin, V. vinifer is likely to e more drought tolernt thn mny Americn Vitis species. Consequently, rootstocks derived from Americn species might tend to reduce vigor nd/or vine cpcity reltive to own-rooted vines in rid regions, where the soil dries down sufficiently to permit implementtion of deficit irrigtion strtegies. The low overll vigor in this study ws lso the reson for the high Y/P rtios, especilly for grfted vines. Rther thn eing generlly overcropped, these vines might hve een clssified s undervigorous. Low θ v or low temperture evidently did not limit fruit set in ny yer; percentge fruit set in ws similr to other yers, lthough hd the lowest θ v etween udrek nd verison nd the lowest temperture during loom. The low yield in ws consequence of low ud fruitfulness comined with low erry weights tht resulted from low soil moisture (McCrthy et l. 1997). Much of the difference in erry size my hve een estlished efore loom, s demonstrted y the smller flower size in compred with the other yers. Thus, while the wter deficit ws not severe enough to reduce fruit set, it my hve een sufficient to limit flower size nd hence erry size (cf. Keller et l. 2010). Rootstock effects on yield formtion vried y scion cultivr, ut nd were often ssocited with high yields. Yield differences rose from comintion of rootstock effects on cluster numer, inflorescence size (flower numer), fruit set, nd erry growth. For instnce, high yields of Merlot on were mostly result of higher erry weights, wheres on they were due to higher erry numers per cluster; other rootstocks hd inconsistent nd opposing impcts on different yield components. In Syrh, resulted in the most clusters with the most flowers nd hence erries, nd the heviest erries. In Chrdonny, on the other hnd, reduced the yield potentil y decresing oth cluster numer nd fruit set, ut compenstory processes in other yield components msked this rootstock effect so tht finl yields were similr cross ll rootstocks nd own-rooted vines. The yield-promoting influence of on Merlot nd Syrh contrsts with cool/humid-climte rootstock tril with Müller-Thurgu (Keller et l. 2001), in which decresed oth erry numer per cluster (n effect it shred with ) nd erry weight. In other dry-climte field trils tht included some of the rootstocks used in this study with irrigted Chrdonny (Stevens et l. ), Syrh (Stevens et l. 2010), Cernet Suvignon (Willims 2010), Mlec (Di Filippo nd Vil 2011), or unirrigted Cernet Suvignon (Nuzzo nd Mtthews 2006), rootstock effects on yield nd its components tended to e minor nd, lthough sometimes significnt, were often inconsistent etween yers. Although rootstocks my sometimes led to considerle differences in scion yield, sesonl effects hve long een deemed to strongly outweigh their influence on fruit composition (Schumnn 1974). The outcomes from the present field tril confirmed this notion. Nuzzo nd Mtthews (2006) found tht fruit ripening of Cernet Suvignon ws quite insensitive to rootstock. Few nd inconsistent rootstock effects on fruit composition were mesured in recent field tril tht included own-rooted Mlec vines (Di Filippo nd Vil 2011). Similr to our study, Ruhl et l. (1988) found tht rootstock effects on TSS were inconsistent nd tht the ph ws higher in grpes from own-rooted compred with grfted Chrdonny ut not Syrh. These uthors lso reported positive correltion etween juice K + (nd in some cses N + ) nd ph. Potssium, sodium (N + ), nd other metl ctions my sustitute for H +, which increses the ph nd thus counters the influence of orgnic cids (Boulton 1980, 1980). The higher ph of Merlot nd Chrdonny fruit from own-rooted vines in our study might hve een consequence of greter cnopy density (Smrt et l. 1985, Morrison nd Nole 1990) resulting from the high shoot numer of these vines. However, [K + ] ws not significntly higher in juice from own-rooted vines. Gong et l. () found similr K + ut higher N + concentrtions in fruit from own-rooted Syrh nd Chrdonny compred with grfted vines, ut we did not mesure N +. While grfting might hve indirectly influenced fruit ph vi cnopy ltertions in Merlot nd Chrdonny, the ph ws insted ltered y vine wter sttus, irrespective of rootstock, in Syrh. The rtes of sugr ccumultion nd orgnic cid (presumly mlte) ctolism decresed nd eventully cesed during the lte ripening period. These chnges were likely ssocited with declining sink strength of the erries ~30 d fter verison nd with declining tempertures in the fll. The continued increse in ph t tht time my hve een consequence of continued K + (nd perhps some N + ) influx vi the phloem (Rogiers et l. 2006). Moreover, the concomitnt
38 Keller et l. decrese of TSS, K +, nd ph with incresing yield nd Y/P is in greement with erlier reserch (Hepner nd Brvdo 1985) nd indictes tht higher yields nd crop lods reduced phloem influx per erry. It ppers tht the more hevily cropped vines were source-limited, which is in greement with the low pruning weights in this tril. This conclusion is further corroorted y the ssocition etween postverison Ψ x nd TSS nd suggests tht implementtion of deficit irrigtion in this vineyrd restricted vine growth, nd consequently functionl lef re, considerly more thn yield formtion (Eich nd Alleweldt 1985). Conclusions The field performnce of three V. vinifer cultivrs (Merlot, Syrh, Chrdonny) ws evluted on six rootstocks nd on their own roots in rid estern Wshington for three yers. One rootstock (99R) ws ndoned ecuse of its poor winter survivl s result of its long vegettive period. Thus, rootstocks with similr chrcteristics cnnot e recommended for regions with short growing sesons nd cold winters. The remining rootstocks induced few, nd often minor, differences in scion performnce. For the most prt, the vrition in growth, yield formtion, nd fruit ripening nd composition ws dominted y scion cultivr, sptil differences cross the vineyrd site, nd climte vrition mong yers. Although own-rooted vines grew more shoots thn grfted vines, nd nd tended to reduce scion vigor, the rootstocks generlly did not impct vine phenology, fruit set, nd plnt wter sttus. The influence of rootstocks on yield formtion depended on the scion cultivr, ut nd were often ssocited with high yields. Nevertheless, the rootstocks hd only minor effects on fruit ripening nd did not consistently lter solule solids, TA, K +, or nthocynin pigments, lthough the ph tended to e higher in fruit from ownrooted compred with grfted vines. It ppers tht in this dry climte vine vigor, reproductive performnce, nd fruit composition were mostly controlled y wter deficit, through the implementtion of deficit irrigtion, while rootstocks hd minor effects tht often depended on their grfting prtner. Literture Cited Boulton, R. 1980. The generl reltionship etween potssium, sodium nd ph in grpe juice nd wine. Am. J. Enol. Vitic. 31:182-186. Boulton, R. 1980. The reltionships etween totl cidity, titrtle cidity nd ph in grpe tissues. Vitis 19:113-120. Cronneu, A. 1985. The erly selection of grpevine rootstocks for resistnce to drought conditions. Am. J. Enol. Vitic. 36:195-198. Currle, O., O. Buer, W. Hofäcker, F. Schumnn, nd W. Frisch. 1983. Biologie der Ree. Meininger, Neustdt n der Weinstrsse, Germny. Dvenport, J.R., R.G. Stevens, nd K.M. Whitley.. Sptil nd temporl distriution of soil moisture in drip-irrigted vineyrds. HortScience 43:229-235. Di Filippo, M., nd H. Vil. 2011. 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