Relationships between xylem vessel characteristics, calculated axial hydraulic conductance and size-controlling capacity of peach rootstocks

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1 Annls of Botny Pge 1 of 5 doi: /o/mp281, ville online t Reltionships etween xylem vessel hrteristis, lulted xil hydruli ondutne nd size-ontrolling pity of peh rootstoks Sergio Tomesi 1, R. Sott Johnson 2, Kevin R. Dy 2 nd Theodore M. DeJong 2, * 1 Diprtimento di sienze grrie ed mientli, Università degli Studi di Perugi, Perugi, Itly nd 2 Deprtment of Plnt Sienes University of Cliforni, One Shields Ave., Dvis, CA 95616, USA * For orrespondene. E-mil tmdejong@udvis.edu Reeived: 11 August 2009 Returned for revision: 15 Septemer 2009 Aepted: 20 Otoer 2009 Bkground nd Aims Previous studies indite tht the size-ontrolling pity of peh rootstoks is ssoited with redutions of sion wter potentil during mid-dy tht re used y the redued hydruli ondutne of the rootstok. Thus, shoot growth ppers to e redued y dereses in stem wter potentil. The im of this study ws to investigte the mehnism of redued hydruli ondutne in size-ontrolling peh rootstoks. Methods Antomil mesurements (dimeter nd frequeny) of xylem vessels were determined in shoots, trunks nd roots of three ontrsting peh rootstoks grown s trees, eh with different size-ontrolling hrteristis: Nemgurd (vigorous), (intermedite vigour) nd (sustntilly dwrfing). Bsed on ntomil mesurements, the theoretil xil xylem ondutne of eh tissue type nd rootstok genotype ws lulted vi the Poiseuille Hgen lw. Key Results Lrger vessel dimensions were found in the vigorous rootstok ( Nemgurd ) thn in the most dwrfing one () wheres vessels of hd intermedite dimensions. The density of vessels per xylem re in Nemgurd ws lso less thn in nd. These hrteristis resulted in different estimted hydruli ondutne mong rootstoks: Nemgurd hd higher theoretil vlues followed y nd. Conlusions These dt indite tht phenotypi differenes in xylem ntomil hrteristis of rootstok genotypes pper to influene hydruli ondutne pity diretly, nd therefore my e the min determinnt of dwrfing in these peh rootstoks. Key words: Prunus, rootstok, vessel dimeter, hydruli ondutne, dwrfing, xylem ntomy, Poiseuille Hgen. INTRODUCTION Most fruit tree speies re propgted y grfting onto rootstoks seleted for speifi edphi onditions, tolerne to pests or diseses, ontrol of sion vigour nd/or induing erly prodution (Wester, 1995). Seleznyov et l. (2008) desried the effet of dwrfing pple rootstoks on shoot development, pointing out tht in trees grfted on dwrfing rootstoks, the nnul numer of vegettive extension shoots deresed nd the nnul numer of florl shoots inresed. The physiologil explntion of these phenomen hs een deted y mny uthors in the pst 70 yers (Wester, 1995). Some studies on pple (Olien nd Lkso, 1986; Cohen nd Nor, 2002) nd peh rootstoks (Weiel et l., 2003) showed tht speifi rootstoks influene shoot growth rte nd stem wter potentil. The pttern of stem wter potentil ourring during the fternoon strongly ffets shoot growth rtes in the field (Bermn nd DeJong, 1997). Bsile et l. (2003), who followed stem wter potentil nd shoot growth rte during single dys nd over growing seson on some of the sme peh rootstoks hrterized y Weiel et l. (2003), found strong orreltion etween stem wter potentil nd shoot growth over dy. Vegettive growth lso hs een orrelted with umultive wter potentil differenes during the first hlf of growing seson (Bsile et l., 2003). In ddition, differenes in stem wter potentil hve een uslly relted to differenes in reltive shoot growth rte mong peh trees on different rootstoks (Solri et l., 2006). Stem wter potentil is strongly influened y stem hydruli ondutne (Tyree nd Sperry, 1988). Low hydruli ondutne n lso limit stomtl ondutne nd therefore lower photosyntheti ssimiltion. Stomtl losure is the primry mens for trees to prevent vittion in xylem vessels during periods of high potentil evpotrnspirtion (Jones nd Sutherlnd, 1991). Thus, stem or root hydruli ondutne influene stem wter potentil nd n govern growth potentil. Hydruli ondutne per unit lef re hs een reported to e less in dwrfing peh rootstoks thn in vigorous rootstoks nd diretly linked to redutions in rootstok hydruli ondutne of genotypes tht hd redued shoot extension growth rtes (Solri et l., 2006; Solri nd DeJong, 2006). Thus, rootstok hydruli ondutne hs een diretly relted to tree vigour in peh trees. This hs provided one explntion for how rootstoks n influene the sion growth in peh trees: hydruli ondutne influenes stem wter potentil (Tyree nd Sperry, 1988), whih, s demonstrted y Bermn nd DeJong (1997), Bsile et l. (2003) nd Solri nd DeJong (2006), is driving vrile of shoot extension. # The Author Pulished y Oxford University Press on ehlf of the Annls of Botny Compny. All rights reserved. For Permissions, plese emil: journls.permissions@oxfordjournls.org

2 Pge 2 of 5 Tomesi et l. Xylem vessels nd size-ontrolling in peh Axil stem hydruli ondutne is funtion of ntomil hrteristis of the xylem, espeilly vessel dimensions (Vermre et l., 2002). Condutnes through pillry tue re theoretilly desried y the Poiseuille Hgen eqution (Ewers nd Fisher, 1989; Tyree nd Ewers, 1991) where the flow is given y the summtion of vessel or trheid lumen dimeters, eh rised to the fourth power. The Poiseuille Hgen lw hs lso een used to lulte theoretil hydruli xylem ondutne of tree stems (Ewers nd Fisher, 1989). Stem hydruli ondutne in trees is relted to xylem vessel numers nd dimeters (Gison et l., 1985). Vessel dimeter ppers to e highly orrelted with hydruli ondutne euse of the importne of vessel dimeter in the Poiseuille Hgen eqution (Ewers nd Fisher, 1989). Sweet herry dwrf rootstoks pper to hve lrger numers of vessels ut smller vessel dimeters thn vigorous rootstoks (Olmsted et l., 2006; Gonlves et l., 2007). The im of the present study ws to test the hypothesis tht xylem vessel hrteristis re orrelted with dwrfing hrteristis of peh rootstoks in whih xylem hydruli ondutne ppers to e min use of dwrfing (Solri et l., 2006, ; Solri nd DeJong, 2006). If true, this would indite tht the numer nd the dimeter of xylem vessels re importnt ftors tht influene dwrfing potentil of speifi rootstok genotypes nd these hrteristis ould eome vlule seletion riteri for future rootstok improvement. MATERIALS AND METHODS The rootstoks used in this experiment were representtive of three different vigour lsses: high (Prunus persi L. Btsh Prunus dvidin hyrid, Nemgurd, seedpropgted), intermedite (Prunus sliin Lindl. Prunus persi L. Btsh hyrid,, vegettively propgted) nd low (Prunus sliin Lindl. Prunus persi L. Btsh hyrid,, vegettively propgted). Commerilly, nd re sold s Controller 9 TM nd Controller 5 TM, respetively. To test whether the xylem vessel hrteristis nlysed were hrteristi of speifi genotypes nd onsistent ross tissue origins, the xylem from three different prts of the tree were nlysed, nmely roots, trunk nd shoots. Root nd trunk xylem smples were olleted from n experimentl orhrd of the University of Cliforni loted in the Kerney Agriulturl Center, Prlier, CA. Trees used for otining root nd trunk smples were ll grfted with the sion ultivr O Henry. All trees were 7 yers old, trined to perpendiulr V (DeJong et l., 1995) nd reeived norml hortiulturl re. During My, 2009, three woody root segments, pprox. 5.5mm in dimeter, were smpled from eh of five trees on eh rootstok. Root smples were olleted from distne of out 20 m from the se of the trunk from three different positions round the se of eh tree. During the sme period smples of trunk xylem tissue (pprox. 1.5 m long 0.5 m wide 0.25 m deep) were extrted from the rootstok trunk elow the grft union using wood hisel. A few dys lter, shoot smples were olleted from the sme rootstok genotypes tht were grown s grfted trees on Nemgurd rootstok for the purpose of growing shoots for vegettive propgtion, in experimentl orhrds on the University of Cliforni Dvis mpus in Dvis, CA. Three shoots with sl dimeter of pprox. 4.5 mm were olleted from eh of five trees per rootstok. All smples were immeditely pled in plsti gs on ie nd susequently stored t 0 8C until setioned. Smples were fresh setioned with mnul mirotome t 150 mm of thikness to otin two ross-setions from eh field smple. The setions were stined with Toluidine-Blue-O to inrese visul ontrst. Photogrphs of the ross-setions were tken with mer (Model Lei 750, Lei, Wetzlr, Germny) mounted on light mirosope (Elipse E 600, Nikon, Tokyo, Jpn). Imges were then quired with DEI-750D softwre (Optronis, Golet, CA, USA). Three photogrphs were mde from eh ross-setion slide: the first t 4 mgnifition to mesure the thikness of xylem tissue, nd the other two t 10 to lulte vessel density nd dimensions onsidering two rndomly seleted fields of view of xylem tissue. Vessels were mesured nd ounted in frequeny lsses, s desried y Soll nd Gil (2002), using omputer grphis progrm (GIMP, freewre; to pste ruled grid t the sme mgnifition onto photogrphs of vessels. The frequeny lsses were estlished t intervls of 30 mm for trunk nd root vessels, nd t 15 mm for shoot vessels. Theoretil hydruli ondutne (k h ;kgmmp 21 s 21 ) ws lulted with the modified Hgen Poisseuille s lw desried y Tyree nd Ewers (1991): k h ¼ pr X n ðdi 4 128h Þ i¼1 where d is the rdius of the vessel in metres, r is the fluid density (ssumed to e 1000 kg m 23 or equl to tht of wter t 20 8C) nd h is the visosity (ssumed to e MPs.s, or equl to tht of wter t 20 8C). A weighted men (W m ) dimeter ws lulted s men lss dimeter per totl numer of vessel produts, divided y the totl numer of mesurements: w m ¼ P n i¼1 V n;lss i d lss i where V n is the numer of vessels in eh lss, d is the men dimeter in eh lss nd T N is the totl numer of vessels per visul field. Sttistil nlyses of the dt were performed with SAS sttistil softwre (SAS Institute, Cry, NC, USA). Tretments were nlysed y one-wy ANOVA with signifine level set t Mens were seprted y Tukey s w- proedure t P ¼ 0.05 (Sokl nd Rohlf, 1969). For shoot nd root mesurements, two rndomly hosen visul fields from eh of two setions of eh of three shoots or roots were determined for eh of five trees to lulte grnd men with n ¼ 5. For trunk vlues, the grnd men vlues (n ¼ 5) were lulted using dt from two rndomly T N

3 Tomesi et l. Xylem vessels nd size-ontrolling in peh Pge 3 of 5 Numer of vessels 40 Shoots Nemgurd Vessel dimeter (µm) Vessel dimeter (µm) Vessel dimeter (µm) FIG. 1 Frequeny distriutions of xylem vessel sizes per visul field in shoots, trunks nd roots of Nemgurd, nd rootstok genotypes. For shoots nd roots eh vlue is the men of two visul fields from two setions per three shoots or roots from eh of five trees + s.e. (n ¼ 5). For trunks eh vlue is the men of two visul fields from four setions of one smple from eh of five trees + s.e. (n ¼ 5). Mens with different lower-se letters re signifintly different t P, 0.05 (Tukey test). hosen visul fields in eh of four setions from eh of five trees. RESULTS Totl xylem thikness of the trunk ws not evluted euse trunk xylem ntomil nlysis ws determined on pthes extrted from the outer lyers of xylem tissue from trunks. However, shoot nd root xylem thikness reltive to their respetive dimeter did not signifintly differ mong rootstoks (dt not shown). The distriution of shoot xylem vessels in different size lsses differed depending on the rootstok genotype. Nemgurd (vigorous) shoots hd high numer of vessels in the mm lss nd low numer of vessels in the lower dimeter lsses (Fig. 1). The most frequent dimeter lss for this genotype ws mm. (intermedite vigour) hd higher numer of vessels in the medin dimeter size lsses (15 30 nd mm) nd lower numers in the low- nd high-dimeter size lsses (0 15 nd mm). (sustntilly dwrfing) hd higher numer of vessels in the mm lss nd low numers in the nd mm lsses. For this genotype there were very few vessels with lrge dimeters. The totl numer of vessels per visul field in shoots lso vried with genotype (Tle 1). hd more vessels per field thn (P, 0.001) nd hd more vessels per visul field thn Nemgurd (P, 0.001). The weighted men vessel dimension (W m ) of shoot xylem ws highest in Nemgurd followed y nd (Fig. 2). Xylem vessel dimensions in trunk xylem lso vried depending on the rootstok genotype. Nemgurd hd high numers of vessels in the two medium size lsses (30 60 nd mm) nd lower numers in the other lsses (Fig. 1). The reltively high numer of vessels in the lrgest dimension lss ( mm) ws hrteristi of this rootstok. hd high numer of vessels in the mm lss with few in the other lsses nd no vessels in the lrgest size lss. hd the highest numer of vessels in the 0 30-mm lss, ut high numers of vessels were lso present in the mm lss. No vessels were TABLE 1. Numer of xylem vessels per visul field in shoots (n ¼ 5), trunks (n ¼ 5) nd roots (n ¼ 5) of Nemgurd, nd rootstok genotypes tok Shoot Nemgurd For shoots eh vlue is the men of two visul fields from two setions per three shoots from five trees + s.e. (n ¼ 5). For trunks eh vlue is the men of two visul fields from four setions from five trees + s.e. (n ¼ 5). For roots eh vlue is the men of two visul fields from two setions per three roots from five trees + s.e. (n ¼ 5). Mens with different lower-se letters re signifintly different t P, 0.05 (Tukey test). Weighted men vessel dimeter (µm) Shoots Nemgurd FIG. 2 Weighted men xylem vessel dimeters in shoots, trunks nd roots of Nemgurd, nd rootstok genotypes. For shoots nd roots eh vlue is the men of two visul fields from two setions per three shoots or roots from eh of five trees + s.e. (n ¼ 5). For trunks eh vlue is the men of two visul fields from four setions of one smple from eh of five trees + s.e. (n ¼ 5). Mens with different lower-se letters re signifintly different t P, 0.05 (Tukey test).

4 Pge 4 of 5 Tomesi et l. Xylem vessels nd size-ontrolling in peh deteted in the two lrgest size lsses ( nd mm). As found in shoots, in trunk xylem the numer of xylem vessels per field vried with rootstok (Tle 1). hd more vessels thn (P, 0.001) nd hd more thn Nemgurd (P, 0.001). W m ws higher in Nemgurd thn in (P, 0.001) nd it ws higher in thn in (P, 0.001). Xylem vessel hrteristis of roots lso differed depending on the rootstok genotype, similr to shoots nd trunks (Fig. 1). Nemgurd hd high numer of vessels in the two medium size lsses (30 60 nd mm) while the other lsses hd lower numers. Agin, Nemgurd hd some vessels in the lrger size lsses ( nd mm). hd high numers of vessels in the nd mm lsses nd lower numers in other lsses nd no vessels in the upper two size lsses. hd the highest numer of vessels in the mm lss, high numers of vessels in the 0 30-mm lss, very low numers of vessels in the mm lss nd no vessels in the two lrgest lsses ( nd mm). As found in shoots nd trunks, the numer of xylem vessels per field in roots vried with the rootstok genotype (Tle 1). hd more vessels thn (P, 0.001) nd hd more vessels thn Nemgurd (P, 0.001). W m ws higher in Nemgurd thn in (P, 0.001) nd it ws higher in thn in (P, 0.001). W m in ll three mesured orgns (shoots, trunks nd roots) vried onsistently mong rootstok genotypes (Fig. 2). Nemgurd hd the lrgest weighted men vessel dimensions in ll orgns followed y nd. In Nemgurd nd there were no differenes etween root nd trunk weighted men vessel sizes ut there were differenes etween the weighted men xylem vessel dimeters of orgns nd shoots for these two ultivrs. By ontrst, in there were differenes etween weighted men vessel dimeters of roots nd trunks, ut not etween trunks nd shoots. Condutne per visul field lulted using the modified Poiseuille Hgen eqution (Tyree nd Ewers, 1991) vried depending on the rootstok genotypes (Fig. 3). Nemgurd hd the highest lulted ondutne in ll the orgns tested, followed y nd then. DISCUSSION Xylem vessel numers nd dimensions vried mong rootstok genotypes in ordne with the vigour of trees when these rootstoks re used with ommeril peh sion genotypes. In ll the orgns tested there were ler differenes in vessel dimeter size lss distriutions. Nemgurd, the most vigorous rootstok, hd lrger xylem vessels thn, the semi-dwrfing rootstok, nd, the more dwrfing rootstok, respetively (Weiel et l., 2003). Weighted men vessel dimeters of the vigorous rootstok ( Nemgurd ) were lso lrger thn the semi-dwrfing nd dwrfing rootstoks ( nd, respetively). This hrteristi ws the inverse of the numer of vessels per visul field (greter in thn nd Condutne (kg m Mp 1 s 1 ) Shoots Nemgurd ). Thus, the most vigorous rootstok hd fewer xylem vessels ut with lrger dimeters thn the dwrfing rootstoks, whih hd more xylem vessels ut with smller dimeters. The vessel dimeter results re similr to those reported y Gonlves et l. (2007) nd Olmsted et l. (2006) for sweet herry rootstoks. However, ontrry to herries the density of vessels per xylem ross-setionl re in the peh rootstoks lso vried. The potentil effet of differenes in xylem hrteristis on hydruli ondutne were refleted in the theoretil ondutne lulted with the Poiseuille Hgen lw. There were ler differenes mong rootstok genotypes orresponding to previously reported vigour hrteristis nd mesured hydruli ondutnes given y Solri et l. (2006). The sle of theoretil hydruli ondutnes in the present study lso orresponded to tht reported y Solri et l. (2006) otined y empiril mesurements of stem hydruli ondutne. The vrition in xylem dimensions in the shoots of different genotypes, even though these rootstok genotypes were ll grfted onto vigorous rootstoks, indites tht the redutions of vessel dimeters of the dwrfing genotypes re proly due to speifi hrteristis driven y geneti ftors. Further studies re neessry to understnd these hrteristis etter. Therefore, the numer nd the dimeter of xylem vessels pper to e key ftors tht influene dwrfing potentil of speifi rootstok genotypes y influening hydruli ondutne. Redued hydruli ondutne, s demonstrted y Solri et l. (2006) nd Solri nd DeJong (2006), n use redutions in stem wter potentil during mid-dy hours (Bsile et l., 2003; Solri et l., 2006). This lower Nemgurd FIG. 3 Clulted xil hydruli ondutne per visul field in shoots, trunks nd roots of Nemgurd, nd rootstok genotypes. For shoots nd roots eh vlue is the men of two visul fields from two setions per three shoots or roots from eh of five trees + s.e. (n ¼ 5). For trunks eh vlue is the men of two visul fields from four setions of one smple from eh of five trees + s.e. (n ¼ 5). Mens with different lowerse letters re signifintly different t P, 0.05 (Tukey test).

5 Tomesi et l. Xylem vessels nd size-ontrolling in peh Pge 5 of 5 wter potentil is the sis for dereses in shoot growth (Bermn nd DeJong, 1997; Bsile et l., 2003; Solri et l., 2006). Thus, xylem vessel hrteristis pper to e importnt ftors relted to the dwrfing pity of grft-omptile peh rootstoks. Furthermore, the theoretil lultion of xylem hydruli ondutne sed on vessel numers nd dimensions per unit of xylem re my e n effetive mens to estimte the dwrfing pity of speifi genotypes. At the prtil level, xylem ntomil mesurements my e useful inditors for prediting rootstok vigour induing hrteristis during erly stges of plnt development in rootstok reeding/development progrmmes. ACKNOWLEDGEMENTS We thnk Dr V. Polito for use of ntomil lortory equipment, Ms K. Pinney for setting up the mirosopi equipment nd relted softwre nd Dr P. Proietti for mking this ollortion possile. LITERATURE CITED Bsile B, Mrsl J, DeJong TM Dily shoots extension growth of peh trees growing on rootstoks tht redue sion growth to dily dynmis of stem wter potentil. Tree Physiology 23: Bermn ME, DeJong TM Diurnl ptterns of stem ex tension growth in peh (Prunus persi): temperture nd flututions in wter sttus determine growth rte. Physiologi Plntrum 100: Cohen S, Nor A The effet of three rootstoks on wter use, nopy ondutne nd hydruli prmeters of pple trees nd prediting nopy from hydruli ondutnes. Plnt Cell nd Environment 25: DeJong TM, Dy KR, Doyle JF, Johnson RS The Kerney Agriulturl Center perpendiulr V (KAC-V) orhrd system for pehes nd netrines. HortTehnology 4: Ewers FW, Fisher JB Tehniques for mesuring vessel lengths nd dimeters in stems of woody plnts. Amerin Journl of Botny 76: Gison AC, Clkin HW, Noel PS Hydruli ondutne nd xylem struture in trheid-ering plnts. Interntionl Assoition of Wood Antomy Bulletin n.s. 6: Gonlves B, Correi CM, Silv AP, et l Vrition in xylem struture nd funtion in roots nd stems of sion rootstok omintions of sweet herry tree (Prunus vium L.). Trees 21: Jones HG, Sutherlnd RA Stomtl ontrol of xylem emolism. Plnt Cell nd Environment 14: Olien WC, Lkso AN Effet of rootstok on pple (Mlus domesti) tree wter reltions. Physiologi Plntrum 67: Olmsted MA, Lng NS, Ewers FW, Owens SA Xylem vessel ntomy of sweet herries grfted onto dwrfing nd non dwrfing rootstoks. Journl of Amerin Soiety of Hortiulturl Siene 131: Seleznyov AN, Tustin DS, Thorp TG Apple dwrfing rootstoks nd interstoks ffet the type of growth units produed during the nnul growth yle: preoious trnsition to flowering ffets the omposition nd vigour of nnul shoots. Annls of Botny 101: Sokl RR, Rohlf FJ Biometry. Sn Frniso: WH Freemn nd Co. Solri LI, DeJong TM The effet of root pressuriztion on wter reltions, shoot growth, nd lef gs exhnges of peh (Prunus persi) trees on rootstoks with differing growth potentil nd hydruli ondutne. Journl of Experimentl Botny 57: Solri LI, Johnson RS, DeJong TM Reltionship of wter sttus to vegettive growth nd lef gs exhnge of peh (Prunus persi) trees on different rootstoks. Tree Physiology 26: Solri LI, Johnson RS, DeJong TM Hydruli ondutne hrteristis of peh (Prunus persi) trees on different rootstoks re relted to iomss prodution nd distriution. Tree Physiology 26: Solri LI, Pernie F, DeJong TM The reltionship of hydruli ondutne to root system hrteristis of peh (Prunus persi ) rootstoks. Physiologi Plntrum 128: Soll A, Gil L Xylem vessel dimeter s ftor in resistne of Ulmus minor to Ophiostom novo-ulmi. Forest Pthology 32: Tyree MT, Ewers FW The hydruli rhiteture of trees nd other woody plnts. New Phytologist, 119: Tyree MT, Sperry JS Do woody plnts operte ner the point of tstrophi xylem dysfuntion used y dynmi wter stress? Plnt Physiology 88: Vermre G, Doussn C, Pges L, Hi R, Pierret A Influene of xylem development on xil hydruli ondutne within Prunus root systems. Trees 16: Wester AD tok nd interstok effets on deiduous fruit tree vigour, preoity, nd yield produtivity. New Zelnd Journl of Crop nd Hortiulturl Siene 23: Weiel A, Johnson RS, DeJong TM Comprtive vegettive growth responses of two peh ultivrs grown on size-ontrolling versus stndrd rootstoks. Journl of Amerin Soiety of Hortiulturl Siene 128: