The Effect of Trellis Systems on the Performance of Vitis vinif era L. cvs. Sultanina and Chenel in the Lower Orange River Region

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1 The Effet of Trellis Systems on the Performne of Vitis vinif er L. vs. Sultnin nd Chenel in the Lower Ornge River Region J.J. Swnepoel1, J.J. Hunter 1 nd E. Arher 1) Vitiulturl nd Oenologil Reserh Institute (YORI), Privte Bg X Stellenbosh, Republi of South Afri ) Deprtment of Vitiulture, University of Stellenbosh, 76 Stellenbosh, Republi of South Afri Submitted for publition: Mrh 199 Aepted for publition: August 199 Key words: Grpevine, trellis system, reprodutive growth, vegettive growth, light, photosynthesis The effet of six trellis systems on the reprodutive nd vegettive performne of Sultnin nd Chene), grown in the lower Ornge River region of South Afri, ws investigted. Lrger trellis systems signifintly inresed the yield of both ultivrs, nd the photosyntheti tivities of the leves t verison s well s the nopy light environment tended to be higher for these systems. The higher yields reorded for Sultnin were ttributed to improved budding perentges, whih were used by improved light environments t the bsl 'buds. The improved yield obtined for Chene! however, ws due to higher bunh msses, whih were most likely used by the higher photosyntheti tivities of the leves. The trellising of grpevines, ommon prtie in the vitiulturl world, leds to ltertions in growth, yield nd fruit omposition through inter li its influene on the mirolimte (Smrt, 195). Positive effets on yield were obtined by enlrging nopy folige (Shulis & My. 1971; Ksimtis, Lider & Kliewer, 1975; Wever & Ksimtis, 1975; Crbonneu, Cstern & Lelir, 197) or inresing the generl dimensions of the nopy, thereby enourging replement shoots to grow upwrds (Shulis & My, 1971; Wever & Ksimtis, 1975). Thin nopies improved sunlight exposure nd photosyntheti pity. Sine diret sunlight in ombintion with the lef re index ontributes the most to totl photosynthesis of the nopy (Crbonneu, 197), nopy of three lef lyers (two exterior nd one interior) is ner the optimum s regrds photosynthesis (Smrt, 197, 195; Fernndez, Blkr & Meyer, 197). The rte of photosynthesis, is, however, ffeted not only by light intensity but lso by intermittent light nd light qulity, temperture, reltive humidity, o nd onentrtions, lef ge, moisture supply, sesonl ptterns nd rop lod (Hunter & Visser, 19 nd the referenes therein). An inrese in yield per vine ws found to be the result of n inrese in luster weight (My, Suer & Sholefield, 1973), the number of berries (Lynn, 1965), berry mss (Crbonneu et l., 197), bud burst (Shulis, Amberg & Crowe, 1966; Shulis & My, 1971; Clingeleffer & My, 191 ), fruitfulness (My et l., 1973; Crbonneu et l., 197; Clingeleffer & My, 191) nd the number of nodes left per vine fter pruning (Ksimtis et l ; My, Clingeleffer & Brien, 1976; Wever et l., 19), or ombintions of these ftors. Sultnin omprises bout 7% ( 17 5 h) of the totl vineyrd re in the lower Ornge River region of South Afri nd is used for drying ( 115 t dried grpes), vinifition ( 3 15 t) nd tble grpes (3 5 t). Grpes other thn Sultnin, suh s Chene! (Chenin bln x Trebbino), Chenin bln nd Colom br, whih re grown for vinifition, re ultivted on 6 h nd ontribute 6 t (Anon., 197). More thn 9% of Sultnin is urrently trined on T trellis, but vriety of trellis systems re used for other wine grpes. Aording to Le Roux (1973), the hrvesting nd pruning of vines trined on the T-trellis is diffiult, nd rows hve to be wide to ommodte the system nd llow for ultivtion prties. The pproprite trellis system for wine grpes is still not known. The im of this investigtion ws to ompre the performne of Sultnin grpevines trined onto the T-trellis with those trined on other systems, nd lso to determine the most suitble system for Chene! in this region. MATERIALS AND METHODS Experimentl vineyrd: A trellising tril with V. vinifer v. Sultnin, ungrfted, s ws the generl prtie in tht re t tht stge, nd v. Chene!, grfted to 99 Rihter (l Ry 13), ws estblished in 1979 t the Upington Agriulturl Reserh Sttion ( 5S; 1 16E) in the lower Ornge River region (limti region V) (Symn, 191). The soil ws lssified s Dundee series ording to the system of MVir et l. (1977) nd is representtive of the lluvil soils long the Ornge River. To sertin the effet of trellis systems, the plnting width ws 3, x 1,5 m, nd len ultivtion nd full surfe-flood irrigtion were pplied. S ultnin ws trined to deentrlised rown-development s desribed by Zeemn & Arher (191 ), resulting in one rown per vine for the smller systems nd two rowns per vine for the T, slnting, swing-rm nd ftory systems. Chene! ws trined to bilterl ordon on the lengthened Pero Id, USA hedge, I,5 m slnting nd T-trellis nd to prllel Aknowledgements: The tehnil ssistne of H.C. Struss. A. C/it:. H.J. Ne/ nd S. Bruwer is grtefully knowledged. S. Afr. J. Enol. Viti., Vol. 11, No.,

2 6 Effet of Trellis System on the Pe1formne of Sultnin nd Chene! x I 3mm -f- 5mm 1mm FIGURE l Digrmmti representtion of the USA hedge trellis. (x=wire positions). bilterl ordons on the ftory system nd Genev Double Curtin. Aording to generl prtie, vines of ll the trining systems were topped twie but no ttempt ws mde to position the shoots. Vines were pruned ording to the Guyot (Sultnin) nd spur (Chene!) pruning systems, respetively, with n initil bud lod of (Sultnin) nd 16 (Chene!) buds per kg shoot mss. Adjustments during the tril led to pruning norm of to 1 nes for sultnin ( to 15 buds per ne) nd buds per kg shoot mss for Chene!. Experimentl design: The tril ws lid out s rndomised blok design with six tretments nd four replites for eh ul ti vr. Eh plot onsisted of 1 tril vines per replite nd border effets were eliminted using border vines nd rows. Tretments (trellis systems) for both Sultnin nd Chene! were : lengthened Perold, 1,5 m slnting trellis,,9 m T trellis, ftory system s desribed by Zeemn ( 191) s well s USA hedge (Steinhuer & Bowers, 1979) (Fig. l). Furthermore, for Sultnin, the swing-rm trellis suggested by Clingeleffer & My ( 191 ), whih ws originlly designed to improve mehnil hrvesting nd to llow the prtil mehnistion of pruning, ws lso used. This trellis ws modified (Fig. 1 b) to llow the independent movement of both rms. The dpttion ws mde in order to djust the trellis to horisontl system during flowering to obtin better light penetrtion in the luster zone of the unfruitful Sultnin. To obtin longer ordon length per vine, omprble to tht of the ftory system, Genev Double Curtin (Shulis et l., 1966) ws used for the more fruitful Chene!. Dt olletion: Dt were olleted during seven sesons (193-'9). Phenologil dt nd the pperne of the +-if-----1mm mm FIGURE lb Digrmmti representtion of the Austrlin swing-rm trellis. (x=wire positions). S. Afr. J. Enol. Viti., Vol. 11, No., 199

3 Effet of Trellis System on the Performne of Sultnin nd Chene! 61 growth-rrestment phenomenon, ommon problem in this region (Symn, 193), were reorded through the growth seson, wheres rop, luster nd berry mss were determined t hrvest. Must sugr ( B) ws mesured using hnd refrtometer, nd totl idity (expressed s g/dm 3 trtri id) ws determined by titrtion with O,lN NOH nd phenolphthlein s n inditor. Fruitfulness (the number of bunhes per bud lloted during pruning), the budding perentge (% lloted buds whih sprouted) nd pruning mss were reorded in winter. Sine infloresene initition ourred prior to bloom (Swnepoel & Arher, 19), nopy density nd photosynthetilly tive rdition (PAR) were reorded in the luster zone t tht stge. Cnopy density ws determined in the luster zone (between the ordon nd first wire) using the point qudrtpriniple of Smrt et l. ( 195), where needle is pssed through the nopy nd the number of ontt points nd the thikness of the nopy reorded. Photosynthetilly tive rdition in the bunh zone s well s mbient rdition bove the nopy were determined with hnd-held quntum sensor (Li-Cor). Photosyntheti tivity (mg CO/dm h) of the middle nd bsl leves ws mesured t bloom nd verison during 19 nd 199 using portble photosynthesis meter (Anlytil Development Compny MK 1) nd instrument prmeters s desribed by Hunter & Visser (19). Reltive humidity (KM humidity meter), temperture nd windspeed (KM 3 thermo-nemometer) were mesured in the entre of the nopy s well s mbient. These mesurements were rried out between 1: nd 1: on loudless dys with mximum mbient tempertures of 5,3 C (Sultnin) nd the following dy 3,3 C (Chene!) t bloom nd 3,5 C (Sultnin) nd the following dy 33, 1 C (Chene!) tverison, respetively. The lengthened Pero Id ws omitted for these mesurements in Sultnin sine this trellis ws hnged to gble system. Sttistil nlysis: The signifine of differenes between trellis systems for ul ti vr ws lulted per ultivr by mens of ftoril nlysis bsed on Tukey's formul (Snedeor & Cohrn, 197) using stndrd YORI sttistil softwre pkge. Furthermore, for the period 196 to 199, stepwise liner regression (Drper & Smith, 191) ws employed to selet those vribles hving strong reltionship with rop mss. RESULTS Phenologil dt: Although the effet of trellis systems on the dte of bud burst (1-13 September) nd full bloom ( 1-3 Otober) of Sultnin nd Chene! ws very smll (dt not shown), vines on the smller vertil systems (lengthened Pero Id nd USA hedge) tended to reh these stges lter thn those on the higher systems. Yield: Generlly, horizontl trellises (1,5 m slnting, T system, ftory nd swing-rm) tended to indue higher verge yields over yers thn the vertil trellises for Sultnin (Tble 1). This onfirms the results of other workers who found tht lrger trellises used inresed yields (Wever & Ksimtis, 1975). Typil of Sultnin, lrge vrition in yield over yers ws observed (dt not shown). Albeit not signifint, berry mss tended to be the highest for the T-trellis but bunh msses showed no definite tendeny. For Chene! the ftory system indued signifintly higher yields thn the vertil systems nd the 1,5 m slnting trellis. The lrger systems tended to inrese bunh msses, but the speifi berry mss showed no tendeny. Growth-rrestment phenomenon: This phenomenon, whih uses loss in yield (Symn, 193), ws observed TABLE 1 Men performne ( ) of Sultnin nd Chene! trined onto different trellis systems in the lower Ornge River region. Trellis system Crop mss (t/h) s Bunh mss (g) s Berry mss/1 berries (g) s Budding (%) Fruitfulness (bunhes/ Cne mss (kg/vine) shoot) s s s Crop:ne mss rtio s Lengthened Perold 1,9 1,7b 3,l 1, I 159, 15,5 59,b 9,6,39 l,5lb,,3b 3,9b 5,lb USA hedge 1,b,b 37,l 19, 15,9 17,9 59,3,9, l,61b,7,7 3,7b,5b 1,5 m Slnting 3,lb 5,3b 7,l 7,5 167,l 1, 66,3 9,,5 l,6b l,9b,b 5, 5,5b T-system, 7,~b,, 169,l 151, 65,b 9,5,l l,77,lb,lb 5,5 6, Ftory, 3,9 39,9 7,5 16,5 1, 66,9 9,, l,63b,,6b,b 5,6b Swing-rm/GDC* 6,,3b 3,7 51,7 166,9 151,3 65,b,6, l,59b,b,3b 5, 6,3 Men,9 6, 396, 3,7 163,1 19,7 63,6 9,9,3 1,6,3,, 5,6 S = Sultnin. C =Chene!. *Swing-rm for Sultnin. Genev Double Curtin for Chene!. Vlues designted by the sme letter do not differ signifintly (p <,5) for eh prmeter nd ultivr. S. Afr. J. Enol. Viti., Vol. 11, No., 199

4 6 Effet of Trellis System on the Pe1formne of Sultnin nd Chene! 1 - LLN I I D I 6- () 3 - LP USA 1,5 s T Fe. SA FIGURE Lef lyer numbers (LLN) nd distne between ontt points (D) mesured in the luster zone of Sultnin trined onto six trellis systems. Vertil brs designted by the sme letter do not differ signifintly (p <,5) for eh prmeter. [LP= lengthened Perold; USA=USA hedge; 1,5 S = 1,5 m slnting trellis; T=T-trellis; FAC=ftory; SA=swing-rm]. - LLN. 1 DD 1 z...i 6 I 6 -() 3 - LP USA 1,5 s T Fe. GDC FIGURE b Lef lyer numbers (LLN) nd distne between ontt points (D) mesured in the luster zone of Chene\ trined onto six trellis systems. Vertil brs designted by the sme letter do not differ signifintly (p <,5) for eh prmeter. [LP= lengthened Perold; USA=USA hedge; 1,5 S = 1,5 m slnting trellis; T=T-trellis; FAC=ftory; GDC=Genev Double Curtin]. S. Afr. J. Enol. Viti., Vol. 11, No., 199

5 Effet of Trellis System on the Pe1formne of Sultnin nd Chene! 63 during two yers only for Sultnin trined on the T-trellis. Budding perentge nd fruitfulness: A signifintly lower budding perentge ws found for Sultnin trined on the vertil systems (Tble 1 ). Though not signifint, the lrger systems, e.g. the ftory system, tended to indue higher fruitfulness. Smll vritions (v =,3%) were observed in the budding perentge of Chene! trined on different trellis systems. The vertil lengthened Perold, however, indued signifintly lower fruitfulness thn the horisontl T-trellis (Tble I). A stepwise vrible seletion proedure, during whih ll vegettive nd reprodutive vribles were used in the regression eqution in order of their importne for redution in the totl sum of squres of Y (rop mss), indited tht the budding perentge ws the most importnt prmeter in delring the vrition in rop mss of Sultnin (R =,). Although the fit of the eqution ws not signifint t 95% level, the vrition in rop mss for Chene!, however, ws minly used by differenes in bunh mss (R =,7). Grpe omposition: Must sugr, whih vried from l,6 B to 3, B for Sultnin, ws the highest for the ftory (3, B) nd the swing rm (3, B) systems, but it ws the lowest for the USA hedge ( l,6 B) nd the T-trellis ( l,9 B ). Totl idity, lbeit very low, ws the highest for the ftory system (,9 g/dm 3 ). For Chene!, the ftory system lso indued the highest (5,5 B) nd the T-trellis nd the USA hedge the lowest (, B) sugr onentrtion, wheres the highest totl idity ws obtined with the 1,5 m slnting trellis ( 6, g/dm 3 ). Cne mss: From Tble I it is evident tht trellis systems hd mrked effet on ne mss, espeilly for Sultnin. For Sultnin the vertil nd the ftory systems indued signifintly higher ne mss, wheres for Chene! the vertil systems nd the T-trellis retrded vigour sine they indued signifintly lower ne msses. The rop: ne mss rtios were, however, very low for the vertil systems for both ultivrs. This ws probbly due to exessive growth whih ould not be ommodted by these systems, the result of whih ws lso poorer grpe development. Cnopy density: Exessive vigour nd too dense nopies re lso depited in the distne between ontt points (leves, lusters, shoots) in the folige. Although the verge lef-lyer number (LLN) for Sultnin during full bloom ws the lowest in the lengthened Perold (5,3) nd USA hedge (5,) nd still not ner the optimum of 3, s suggested by Smrt (195) for low-vigour vines, the distnes between ontt points were similrto those of the horisontl systems, suggesting nopies of omprble densities (fig. ). Although the nopies were denser in the se of Chene!, similr tendeny ws obtined (Fig. b). Cnopy mirolimte: Photosynthetilly tive rdition, mesured in the luster zone during full bloom for Sultnin, s well s tht expressed s perentge of mbient light intensity, ppered to be very low in generl. Although -(/) C\I E w ::L PAR % x 1 1 ~ 6 )> 3 C" CD 6 LP USA 1,5 s T Fe. SA FIGURE 3 Photosynthetilly tive rdition (PAR) nd perentge of mbient PAR mesured in the luster zone of Sultnin trined onto six trellis systems. (LP=lengthened Perold; USA=USA hedge; 1,5 S = 1,5 m slnting trellis; T-T-trellis; FAC =ftory; SA = swing-rm). S. Afr. J. Enol. Viti., Vol. 11, No., 199

6 6 Effet of Trellis System on the Pe1formne of Sultnin nd Chene! -.. M ' E "O '15 C"I () O> E -Cl) 1 ro I- {) Cl).. 5 > (/).... -Bloom Cillill] V.. er1son USA 1,5 s T Fe. SA FIGURE Speifi photosyntheti rte mesured for the middle leves during bloom nd verison for Sultnin trined onto five trellis systems (lengthened Perold omitted). [USA=USA hedge; 1,5S=l,5m slnting trellis; T=T-trellis; FAC=ftory; SA=swing-rm] M ' E "O "N () -O> E 15 - Bloom Hm+I Verison {) 1 Cl).. >- (/) LP USA 1,5 s T Fe GDC FIGUREb Speifi photosyntheti rte mesured for the middle leves during bloom nd verison for Chene! trined onto six trellis systems. [LP=lengthened Perold; USA=USA hedge; 1,5S=l,5m slnting trellis; T=T-trellis; FAC=ftory; GDC=Genev Double Curtin]. S. Afr. J. Enol. Viti., Vol. 11, No., 199

7 Effet of Trellis System on the Pe1jormne of'sultnin nd Chene! 65 not signifintly, it ppers to be lower in the vertil USA hedge thn in the horisontl ftory system (Fig. 3). This ws lso observed during verison, with mesurements s low s,% of mbient light intensity for the USA hedge. For Chene!, the vertil systems lso tended to indue the lowest PAR vlues (,1 %) t verison (dt not shown). Furthermore, good reltionship between PAR nd the distne between ontt points (nopy density) ws obtined for Sultnin (r=,79). Although no signifint differenes were obtined between trellis systems onerning temperture, reltive humidity nd winds peed in the nopy during full bloom nd t verison (dt not shown), higher nopy tempertures (5,7 C; 33, C) were reorded for Sultnin trined on the T-trellis thn in the other systems (3,9 C; 3,5 C). Speifi photosyntheti tivity: Although the speifi photosyntheti tivity of the middle leves ws higher thn tht of the bsl leves, the differenes between trellis systems for suh leves were similr to tht observed for the bsl leves. Therefore, only the results of the middle leves re disussed. The speifi photosyntheti rtes of the middle leves of Sultnin during full bloom were higher for the T-trellis thn for the ftory nd lso tended to be higher thn for the other systems, wheres during verison the 1,5 m slnting nd ftory trellises tended to indue higher rtes (Fig. ). In ontrst to tht observed for Sultnin, trellis systems hd no effet on the photosyntheti rte of Chene! during full bloom (Fig. b). Photosyntheti rtes, whih tended to be the highest in the vertil systems t bloom, were the lowest in these trellises during verison. The photosyntheti rtes generlly deresed from full bloom to verison for both ultivrs, onfirming the results of Hunter & Visser ( 19). Stomt! resistne vlues for both ultivrs were very low t full bloom (-,3 s/m), but t verison (between I, 11 nd 5, s/m) it ws omprble to those found for otherultivrs s quoted by Hunter & Visser (19). In ontrst to the findings of these uthors, trnspirtion rte inresed from full bloom to verison (dt not shown). This phenomenon n probbly be explined by the higher mbient s well s nopy tempertures t verison, resulting in higher trnspirtion. DISCUSSION In view of the smll effet of trellis systems on the dte of bud burst, higher ordon development should rther be employed to overome the problem of lte frost (up to mid Otober). Sine trellis systems hve smll effets on the dtes of bloom, whih ourred during the lst hlf of Otober, nopy mngement prties suh s sukering nd shoot positioning should ommene t this dte, irrespetive of trellis system nd ultivr, to ensure n optimum light environment for infloresene formtion. Higher yields of Sultnin in this study were due minly to n improved budding perentge whih onfirms the results of Shulis et l. ( 1966), Shulis & My ( 1971) nd Clingeleffer & My ( 191 ). Improved budding perentges in the lrger systems were primrily used by more effiient ommodtion of vegettive growth resulting in n improved light environment in the nopy, lthough tht improvement ws very smll. A higher budding perentge ws lso obtined by Hunter & Visser (199) fter prtil defolition (improved light environment) of Cbernet Suvignon. If pproximtely 1, kg (nes per vine retined during pruning) ws dded to the verge ne mss, the even lower rop: ne mss rtios indited serious misblne between yield nd growth. Mss per ne s well s shoot length ould hve been more urte indition of the vigour. Photosynthetilly tive rdition levels of bout 1 me/m /s were well below the minimum of 36 me/m /s required for infloresene formtion (Buttrose, 1969) nd were used not only by denser nopy but probbly lso by lrger leves. The pprently higher bunh msses found for Chene! when trined on lrger trellises resulted in higher yields ompred to those of the smll vertil trellises. This onfirms the findings of other reserhers who reported n inrese in yield by enlrging the nopy folige, either by widening the trellis (Shulis & My, 1971; My et l., 1973) or by inresing the height of the nopy (Sholefield, My & Neles, 1977). The former used n inrese in the mount of diret solr rdition interepted by the folige, s found by Crbonneu et l. ( 197) nd Kliewer ( 19) nd, therefore, would result in higher photosyntheti pity of the nopy (Smrt, 197, 195). Although no differenes ould be found in the budding perentge of Chene! trined to different trellis systems, the lrger nopies inresed bud fruitfulness. This n be sribed to less dense nopies, resulting in n improved light environment in the luster zone. The fruitfulness vlues obtined for both ultivrs, however, lerly showed tht Chene! is still reltively fruitful t rdition levels where Sultnin is unfruitfui. In generl, the lower vertil trellis systems, i.e. the lengthened Perold nd USA hedge, resulted in high photosyntheti tivities of the leves t full bloom ompred to those of the lrger systems. This ws probbly due to less leves exposed to diret sunlight in the former systems, using the leves to ompenste, nd therefore higher speifi photosyntheti tivities were reorded. This ws lso found by Hunter & Visser ( 19). This onfirms the generl oneption mong vitiulturists tht nopy mngement prties suh s sukering, shoot positioning, tipping, topping nd lef removl re neessry to hieve the optimum potentil of trellis system for given in-row sping. The lower photosyntheti tivities during verison in the vertil trellises probbly resulted from the higher densities of the nopies t tht stge nd, therefore, resulting in deresed yields. The high sugr ontent of 3 B of Sultnin found for the ftory nd swing-rm t.rellises, together with the higher yields in omprison with the vertil systems, my result in more risins of better qulity. The higher levels were probbly used by better nopy exposure nd the improved light environments reted by these nopies. From the sugr nd id nlyses s well s smll differenes in the nopy mirolimte of Chene!, very little differenes in the wine qulities of grpes hrvested from different trellis systems re expeted. CONCLUSIONS By influening the mirolimte, espeilly the light envi- S. Afr. J. Enol. Viti., Vol. 11, No., 199

8 66 Effet of Trellis System on the Poformne of Sultnin nd Chene! ronment, trellis systems exerted n importnt influene on the reprodutive nd vegettive performne of both Sultnin nd Chene!. An improvement over the reprodutive performne of vines on the T-system ( trellis ommonly used in the lower Ornge River region for the ultivtion of Sultnin) ws obtined with the ftory nd swing-rm trellises, wheres the vertil trellises (lengthened Perold nd USA hedge) performed poorly. This improved performne of the two lrger systems for Sultnin ould hve been more pronouned hd the soil volume (lrger in-row sping) been enlrged nd the vilble nopy volume utilised. Furthermore, system suh s the lyre trellis s proposed by Crbonneu & Cstern ( 196) in ombintion with lef removl my overome the problems of too muh vigour. The improvement in yield ws due minly to less dense nopies using better light environment, whih resulted in higher budding perentges, espeilly in the se of Sultnin. Furthermore, the higher speifi photosyntheti tivities nd, therefore, probbly lso the totl photosyntheti tivities found for the lrger nopies during verison, ould be responsible for the higher bunh msses obtined for Chene! with onomitnt inrese in yield. Sine ll the nopies for both ultivrs were generlly too dense nd not ner the optimum density of three, the differenes in yield, budding perentge, fruitfulness, PAR nd photosyntheti tivities ould hve been more pronouned hd the nopies been mnged orretly. Sine nopies were denser nd rdition levels lower for the more fruitful Chene!, it is evident tht Sultnin needs higher levels of rdition to improve fruitfulness in this ultivr. Furthermore, lthough Chene! ws still reltively fruitful under poor light onditions, its fruitfulness ws influened to lrger extent by poor light environment thn tht of the unfruitful Sultnin. This spet needs to be investigted further. LITERATURE CITED ANONYMOUS, l 97. Sttistieke vn wingerdstokke soos op 3 November l 97. KWV, P.O. Box 5, 76 Prl, Republi of South Afri. BUTTROSE, M.S., Fruitfulness in grpevines: effets oflight intensity nd temperture. Bot. Cz. 13, CARBONNEAU, A., l 97. Stress moderes sur feuillge induits pr le systeme de onduite et regultion photosynthetique de l vigne. In: Bourd, J. & Pouget, R., (eds.). Physiologi de l Vigne. Bordeux, - 7 June l 96. OIV rue Roquepine F-75, Pris, Frne. pp CARBONNEAU, A. & CASTERAN, P., 196. Optimiztion of vine performne by the lyre trining systems. In : Lee, T. (ed.). Pro. of 6th Austrlin Wine Industry Tehnil Conferene, 1-l 7 July 196, Adelide, South Austrli. pp CARBONNEAU, A., CASTERAN, P. & LECLAIR, Ph., 197. Essi de determintion en biologi de l plnt entiere. Lie reltions essentills entre le biolimt nture!, l physiologi de l vigne t l omposition du risin. Ann. Amelior. Plnt., I CLINGELEFFER, P.R. & MAY, P.. 19 l. The swing-rm trellis for Sultn grpevine mngement. S. Aji-..!. Eno/. Viti., 37-. DRAPER, N.R. & SMITH, H., l 91. Applied regression nlysis. 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