OF "THOMPSON SEEDLESS" GRAPEVINES

EFFECT OF TIME AND SEVERITY OF DEFOLIATION ON GROWTH OF ROOTS, TRUNK, AND SHOOTS OF "THOMPSON SEEDLESS" GRAPEVINES W. MARK KLIEWER and R. D. FULLER Respectively Assciate Bichemist, Department f Viticulture and Enlgy, Davis, 95616, and Research Viticulturist, Paul Massn Vineyards, Sledad, Califrnia 93960. Presented at the Annual Meeting f the American Sciety f Enlgists, Mnterey, Califrnia, June 23, 1973. The authrs thank the Califrnia Wine Advisry Bard fr partial supprt f this research. Accepted fr publicatin May 21, 1973. ABSTRACT The effect f leaf remval n accumulatin f dry matter in grapevine parts was evaluated in a pt experiment n nnfruiting rted cuttings f Vitis vinifera L., 'Thmpsn Seedless'. Defliatin was 0 (cntrl), 25, 50, and 75% (herein called OD, 25D, 50D, and 75D vines), perfrmed at three different times ; simulated fruit-set (SET), veraisn (VER) and fruit maturity (MAT), ver a perid f 2 years. The 25D and OD vines did nt differ significantly in dry weights, regardless f time f defliatin. Dry weights (DW) f canes, trunk, and rts were significantly lwer in vines defliated 50 and 75% at fruit-set than in OD vines. With defliatin at veraisn, hwever, nly the trunk and rts f 50D and 75D vines had lwer DW than OD vines. At harvest, nly rt DW frm 50D and 75D vines was significantly less than in OD vines. Ttal leaf area was related psitively t ttal rt DW. Trunk DW was affected mst by defliatin, fllwed by DW f rts and canes. Ttal cane length and average internde length were significantly less in 75D-SET vines than in OD vines and in all ther defliated vines at all defliatin times except fr 50D-SET and 75D- VER vines. All levels f defliatin at fruit-set significantly increased the number f laterals, thugh defliatin at later dates did nt. DW per unit length f cane and number f mature ndes per vine were nt affected significantly by time r amunt f defliatin. There were n significant interactins between time and amunt f defliatin n any f the parameters measured. Previus investigatins (5,6,7,8,9) n defliatin f grapevines have dealt mainly with effects n fruit grwth and cmpsitin, and crp yields. Investigatins dealing with the effects f defliatin n grwth f ther parts f grapevines, such as rts, trunk, and shts, are scarce. An exceptin is the wrk f Buttrse (1), wh shwed that reductin in leaf area f ptted 'Muscat f Alexandria' vines reduced, in rder f decreasing degree, the grwth f rts, berries, shts, and trunk. Hwever, neither the time nr the effects f defliatin fr mre than 1 year were investigated. Fr a mre extensive review f the literature dealing with defliatin f grapevines, the reader is referred t Kliewer (5), Kliewer and Antcliff (6), and Kblet (8). With mechanical harvesting f grapes at hand, 59 which may result in lss f ttal vine leaf area between 20 and 95% during the harvesting peratin (10), it is imperative that bth the shrt and lng term effects f defliatin n grwth f all parts f grapevines and n vine prductivity be evaluated. The present investigatin was undertaken t determine hw different amunts f defliatin at varius stages f vine develpment ver a tw year perid affects the grwth f rts, trunk and shts f 'Thmpsn Seedless' grapevines. MATERIALS AND METHODS One-year-ld, virus-free, nnfruiting, rted cuttings f Vitis vinifera L. 'Thmpsn Seedless' (syn. 'Sultana'), with tp grwth pruned t a tw-bud spur and rts t 15-20 cm length were used in

EFFECT OF DEFOLIATION---60 this investigatin. The rtings were numbered, weighed, and then divided int 12 grups f 10 vines each s that each grup had rtings representative f the entire range f weight classes. This was dne t take int accunt the large variability in riginal rting weights, which ranged frm 90 t abut 140 g. Percent dry matter f 12 additinal rfings, representing all weight classes, was determined after the rtings were dried in a frced draught ven at 70 C. The rtings were planted in 3-gal cans n March 23, 1971 in a mixture f sil, sand, and peat (2:2:1, v/v/v), and placed in a lathhuse cvered with plyprpylene shade fabric that reduced light intensity abut 50 %. Wd shavings were placed arund the cans t reduce the daily fluctuatins in rt temperatures and water lss. Bud break was abut April 20 in 1971 and March 27 in 1972. There were 12 treatments in the experiment ~ fur levels f defliatin (0, 25, 50, and 75%), hereafter referred t as OD, 25D, 50D, and 75D, initiated at three different times during the grwing seasn. The times crrespnded t fruit-set (SET), veraisn (VER), and fruit maturity (MAT) f nearby 'Thmpsn Seedless' vines grwing in the University vineyard at Davis. Hence, fr example, 25D-SET vines means vines defliated 25% at fruit-set. Each treatment was replicated 10 times except the cntrl (OD), which was replicated 30 times, with each rting serving as a replicate. The initial dates f defliatin fr the three times were June 20, August 7, and September 23 in 1971, and June 2, July 17, and September 1 in 1972. Twentyfive percent defliated vines cnsisted f remving every furth leaf n every sht and lateral, 50D cnsisted f remving every secnd leaf, and 75D designates remving cnsecutively 3 ut f every 4 leaves n every sht and lateral. The terminal 1 r 2 leaves at the sht tips were nt remved. Leaves emerging after the initial defliatins were remved in the same sequence and prprtins as described abve at mnthly intervals. Hwever, after the September defliatins there was little further sht grwth. Tw shts were retained n each rting in 1971 and 4 shts in 1972. All ther shts were remved befre they were 5 cm lng. Each sht was trained hrizntally n a wire abut 2 ft frm the grund and 1 ft apart, with ne sht per trellis wire. All clusters were remved frm shts shrtly after bud break; hwever, mst shts had n clusters. Leaf area per vine in 1971 was estimated by determining the rectangular area (length times width) f each leaf blade and summing the values. The relatinship between planimeter area and rectangular area f a leaf was determined, and is described by the equatin Y=0.619 + 0.603X in which Y=planimeter leaf area and X= rectangular leaf area (3). The crrelatin cefficient was 0.98. In 1972, leaf areas were estimated by determining TABLE 1 Effect f Time and Amunt f Defliatin n Estimated and Theretical Leaf Area Per Vine Amunt f Time f Estimated leaf area Theretical defliatin defliatin cm2/vine % f cntrl leaf area (% f leaves per vine remved) 1971 1972 1971,~ 1972 t, 1971 1972 % 0 -- -- 3987 10,048 100 100 100 25 June 20 June 2 2940 7,976 73.7 79.4 75 50 June 20 June 2 2067 5,753 51.8 57.2 50 75 June 20 June 2 1213 3,774 30.4 37.5 25 25 Aug. 7 July 17 3807 7,983 95.4 79.4 75 50 Aug. 7 July 17 2507 6,056 62.8 60.2 50 75 Aug. 7 July 17 1541 3,749 38.6 37.3 25 25 Sept. 23 Sept. 1 4000 7,456 100.3 74.2 75 50 Sept. 23 Sept. 1 2620 4,988 65.7 49.6 50 75 Sept. 23 Sept. 1 1316 3,733 33.0 37.1 25 a In 1971, leaf area was estimated by length-width measurements taken 20 days after the initial defliatins, using the crrectin factr described in Materials and Methds. b In 1972, leaf area was estimated by determining the rati between dry weight f leaf blades and the planimeter leaf area and multiplying the ttal dry leaf blade weight per vine at final harvest by the factr 178.6 cm2/g dry wt.

61--EFFECT OF DEFOLIATION dry weight-leaf area ratis as described previusly (5,6). In December 1971, after natural leaf fall, half f the replicates f each treatment were harvested. The rts were washed free f ptting sil, and the vines were divided int canes, trunk, and 1-yearld rtlets. The trunk in this cmmunicatin designates the riginal rting at the time f planting, which included several 15-20 cm length rts as well as a tw-nde spur. When referring t DW f trunk, the weight f the parent rting is nt included. Laterals were remved frm the canes and kept as a separate sample at harvest. Cane and lateral length, number f laterals per cane, and number f mature, immature, and ttal ndes per cane were determined after leaf fall. A lateral in this cmmunicatin is defined as a sht, arising frm an auxilliary bud, that is 2 cm r mre in length. Ndes and adjacent interndes that were hardened and brwn in clr were designated as mature. After drying fr several days at 70 C, all parts f the vines were then weighed. In 1972, the same harvesting prcedures were used as in 1971, except the vines were harvested in late Octber, just prir t natural leaf fall. Als, DW f leaves at final harvest, as well as f leaves defliated earlier, were determined. Significant, as used in this reprt, indicates that treatment means are different at the 5 % level r less. RESULTS Leaf area per vine: Agreement between the estimated leaf area, determined either by length-width measurements (1971) r by dry weight-leaf area rati (1972), and theretical leaf area per vine (as indicated by percentage f leaves remved) was reasnably gd, except fr the 25D-VER and-mat vines in 1971 (Table 1). As pinted ut previusly, the 25D, 50D, and 75D treatments were based n leaf number rather than leaf area, and this may accunt fr sme f the discrepancy between the theretical and estimated leaf areas. Effect f time f defliatin n dry weights: In general, the later the time f defliatin the greater the dry matter accumulatin in the canes, trunk, and rts (Table 2). Hwever, nly in rts frm vines defliated September 23, 1971, was the DW significantly greater than in rts frm vines defliated at earlier dates (Table 2). Effect f severity f defliatin n dry weights: The DW f trunk and rts f 50D and 75D vines were TABLE 2 Effect f Time and Amunt f Defliatin n Dry Weight f Whle Vine and Cnstituent Parts~ Amunt f defliatin % Time f Leaves b Canes Trunkd Rts Ttal vine defliatin (g) (g) (g) (g) (g) 1971 1972 1972 1971 c 1972 1971 1972 1971 1972 1971 1972 0 -- -- 64.1 29.1 75.0 12.2 44.6 63.2 106.2 107.5 316.6 25 June 20 June 2 68.8 29.8 78.3 10.4 51.7 59.0 97.2 94.4 328.9 50 June 20 June 2 73.0 22.0 70.0 5.6 25.8 54.3 83.6 88.5 270.8 75 June 20 June 2 77.2 18.3 50.3 0.9 14.7 46.4 78.5 69.3 230.5 25 Aug. 7 July 17 69.2 26.8 81.1 9.9 38.8 60.3 103.6 101.5 315.0 50 Aug. 7 July 17 73.5 26.5 84.1 4.5 39.5 48.3 87.9 82.4 310.1 75 Aug. 7 July 17 71.1 26.3 54.2 1.5 17.0 37.6 74.4 69.9 238.2 25 Sept. 23 Sept. 1 62.2 26.1 71.9 14.1 41.1 72.1 94.6 116.2 292.9 50 Sept. 23 Sept. 1 61.3 25.5 66.9 10.7 44.8 49.9 90.5 88.9 285.0 75 Sept. 23 Sept. 1 68.7 27.2 68.0 5.5 36.6 52.8 81.9 88.3 279.8 LSD at 5% level 8.6 6.5 15.1 4.5 12.7 8.4 14.2 13.5 37.3 a Data are the mean f 5 replicates, except fr the cntrls, which are the mean f 15 replicates. b Dry weight f leaves per vine includes the weight f leaves remved at the initial defliatin, fllw-up defliatins, as well as that at final harvest. c Data represent the mean f 10 replicates, except the cntrl, which is the mean f 30 replicates. d Parent trunk weight at time f planting is nt included. Amer. J. Enl. Viticult., Vh 24, N. 2, 1973

significantly less than in OD (cntrl) and 25D vines in bth 1971 and 1972 (Table 2). Increasing severity f defliatin decreased the DW f canes and increased the ttal DW f leaves (leaves n vines at harvest as well as thse remved earlier). Hwever, the differences between defliated and undefliated vines were nt significant. Effect f time and severity f defliatin n dry weights" Increase in severity f defliatin increased the percentage f ttal leaf dry matter per vine. Hwever, nly in 50D and 75D-SET (1972) was the ttal leaf DW per vine significantly greater than in the cntrl vines. (Table 2). Cane DW f 75D-SET vines in bth 1971 and 1972, and als at veraisn in 1972, was significantly less than in all ther treatment, except 50D-SET (1971) vines. Cane DW in the latter treatment was significantly less than in cntrl vines, but nt significantly less than in ther defliated vines. The 25D treatment, regardless f time, had n significant effect n cane DW (Table 2), nr did 50D-VER, 50D-MAT, and 75D-MAT. Dry weight f trunk (nt including parent trunk weight at time f planting) was significantly less in 50D and 75D-SET and VER vines (1971 nly) than in OD and 25 vines (Tables 2 and 3). N level f defliatin at harvest significantly reduced trunk DW, except 75D in 1971. Hwever, trunk DW f vines defliated 75D was less than that f 50D vines, at every defliatin except harvest in 1972. At nne f the defliatin times was trunk DW significantly reduced at the 25D level, cmpared t OD vines (Table 2). There was a highly significant psitive relatinship between leaf area and rt DW (Figure 1). Rt DW f 50D and 75D vines at each f the three defliatin times in bth years was significantly less than in OD vines (Tables 2 and 3). Dry weight f rts frm 25D vines was als usually less than in OD vines, althugh, the differences were nt significant. Hwever, rt weight in 25D vines was significantly greater than in 75D vines at each f the three defliatin times in bth years, and als greater than in 50D vines n several dates (Table 2). Ttal vine DW were significantly less in. the 50D and 75D vines at all dates in 1971, and als in the June 2 defliated vines in 1972, than in OD vines (Table 2). Ttal vine DW in 75D-VER vines (1972) was als significantly reduced cmpared t the cntrls, but nt n 75D-MAT vines. Ttal DW f 25D vines at all dates were nt significantly less than that f OD vines, nr was DW f 50D-VER and -MAT vines in 1972 significantly less than that f the cntrls. Significant reductin in dry matter accumulatin in vines defliated in September (harvest time) generally ccurred nly in the rts (Table 2). An exceptin were the 75D-MAT vines (1971), in which trunk DW was less than half that in OD vines. 150 EFFECT OF DEFOLIATION---62 140 Nt Defliated Defliated June 2 134 Defliated July 17 120 A Defliated Sept. 1 110 /% n /% IB 100 /% ~,,,.,,..,,,~e A,0 80 /%/% 70, t 5O 40 1 2,000 [3 I 1 1! I 1 I 4.00 0 6,000 8,000 10,000 LEAF AREA PER VINE (cm 2) Figure 1. Relatinship between leaf area per 'Thmpsn Seedless' vine and rt dry weight. 100 90 1971 70 t / /O Defliatin 50 ~ Cane 110 30 / & Trunk 90..I / ~ / Defliatin fr 10 /, ~ Rts, 70 ~./ O Cane I--.~-"~ /%Trunk " 50 O 90 C 30 70 110~ ' ' [ ~9 ~ a D. 50 90-10 ' ~ ~ 1 ' 50 i Amer. J. Enl. Viticuit., Vl. 24, N. 2, 1973 ' f,0 1972 e Rts LYl L ' L I I 1 30 I 1 A 1000 2000 3000 4000 3000 5000 7000 9000 LEAF AREA PER VINE-cm 2 Figure 2. Dry weights f cane, trunk, and rts f 'Thmpsn Seedless' vines defliated at simulated fruit-set, veraisn, and fruit maturity in 1971 and 1972, expressed as percenta.ges f the crrespnding cntrl values (n defliatin) against mean leaf area per vine. Cane and internde length, number f laterals, and cane maturity: Ttal cane length per vine in 75D-SET and VER plants (1972) was significantly less than in OD vines (Table 3). Ttal cane length f 75D-SET vines was als less than in 25D-SET vines. Hwever, differences in cane lengths amng all ther treatments were nt significant. Interndes f 75D-SET vines were significantly shrter than in 0D and 25D vines in 1971 and 1972, and als in 50 D vines in 1972 (Table 3). Internde length in 75D-VER vines in 1972 were als significantly shrter than in 0D and 25D vines. Hwever, differences in length f interndes amng all ther treatments were nt significant.

63--EFFECT OF DEFOLIATION All levels f defliatin n June 2, 1972, significantly increased the number f laterals per vine cmpared t undefliated vines. Hwever, defliatin at veraisn and at harvest had n effect n lateral frmatin (Table 3). Dry weight per unit length f cane, ttal number f ndes per vine (excluding ndes n laterals), and ttal and percentage mature mature ndes per vine were nt significantly affected by time r amunt f defliatin (Table 3). DISCUSSION The extent t which the dry matter accumulatin in canes, trunk, and rts was affected by leaf reductin at different time f defliatin is expressed as a percentage f crrespnding cntrl values in figure 2. These data reveal that, at mst levels and time f defliatin, dry matter accumulatin in the trunk was mst severely reduced, fllwed in rder by rts and canes. These data indicate that pruning weights f canes wuld nt be a gd indicatr f reduced vine capacity due t lss in leaf area, especially if defliatin ccurred at veraisn r later. Buttrse (1) fund that a decrease in leaf area f 'Muscat f Alexandria' vines reduced rt dry weight mst severely, fllwed by that f berries, shts, and trunk, in direct cntrast t ur results. Hwever, in his investigatin, number f leaves was maintained at fixed levels by sht pruning, whereas shts were allwed t grw cntinually in ur study. Furthermre, Buttrse used ttal dry weight f trunk, which included ne year's grwth, befre treatments were initiated, fr calculating percentage decrease in dry weight. In ur wrk, we did nt include the weight f the parent rting in the dry weight f the trunk. In anther experiment, Buttrse (2) varied the number f berries per plant frm 0 t 90 and kept the number f leaves per plant cnstant at 3. He fund that the level f starch in the trunk was greatly reduced with increasing crp level, but dry matter per unit length f sht and trunk were nly slightly less than in vines with n fruit and rt dry weight was nt reduced at all. T evaluate efficiencies f carbn dixide assimilatin in vines defliated t varius degrees, the net assimilatin rates (NAR), i.e., the increase in dry weight per unit leaf area per unit time, were calculated. Only vines defliated at fruit-set were used fr these calculatins. Ttal leaf area per vine at veraisn was used as an estimate f the average leaf area per vine fr the grwing seasn in cntrl vines; but, in defliated vines, leaf area per vine at harvest was used. This was dne t cmpensate fr leaves nt remved prir t fruit-set in defliated TABLE 3 Effect f Time and Amunt f Defliatin n Cane and Internde Length, Dry Weight Per Centimeter f Cane, and Number f Laterals, Ndes, and Mature Ndes Per Vine Amunt f defliatin % N. f Avg N. f - mature Ttal Cane internde Avg dry wt. Avg n. f ndes ndes x Time f length f length per cm cane laterals per per defliatin vine (cm) (cm) (mg) per vine vine a vine 1971 1972 1971 1972 1971 1972 1971 1972 1971 1972 1972 1972 0 / -- -- 223.5 660.1 4.91 4.98 120 106.9 20.8 22.2 132.1 91.8 25 June 20 June 2 216.7 602.0 4.58 4.68 120 120.3 21.6 32.7 127.7 92.7 50 June 20 June 2 200.5 567.4 4.26 4.67 110 112.0 25.4 39.0 123.0 89.2 75 June 20 June 2 166.9 422.0 3.66 3.41 110 115.0 25.4 36.2 124.4 90.8 25 Aug. 7 July 17 248.0 640.4 4.64 5.05 120 120.8 16.2 26.6 126.8 91.2 50 Aug. 7 July 17 210.0 663.6 5.06 4.99 120 117.0 15.0 28.2 131.0 96.2 75 Aug. 7 July 17 279.4 508.8 5.34 4.37 110 96.4 14.8 25.8 116.0 80.2 25 Sept. 23 Sept. 1 239.4 646.6 4.74 5.10 120 106.6 19.4 21.0 127.2 91.8 50 Sept. 23 Sept. 1 230.0 639.5 4.52 4.91 110 100.0 14.0 18.3 130.2 92.8 75 Sept. 23 Sept. 1 222.2 651.4 4.36 5.19 120 100.0 20.0 18.6 126.0 88.2 LSD at 5% level N.S. 151.0 0.81 0.59 N.S. N.S. 7.2 6.6 N.S. N.S. a Number f ndes and number f mature ndes per vine include nly ndes n the primary sht (cane), and des nt include thse n laterals.

vines. The estimated NAR in units f grams dry matter per dm 2 leaf area per grwing seasn fr vines defliated 0, 25, 50, and 75% were, respectively, 3.3, 4.1, 5.5, and 7.8 in 1971, and 3.3, 3.3, 3.6, and 4.8 in 1972. In terms f mg dry matter per dm 2 per day (assuming a 180-day grwing seasn), the NAR ranged frm 18.3 t 43.3 respectively, fr undefliated and 75%-defliated vines. Althugh these values are crude apprximatins f NAR, they d indicate that leaf efficiency increased with decrease in leaf area. Several investigatrs (1,2,4,6,9) have shwn that, as the size f the phtsynthetic surce (leaf area) decreases with respect t the size f the sink (rts, shts, and trunk), the phtsynthetic efficiency increases. Remval f leaves frm vines during rapid sht elngatin (fruit-set), regardless f amunt, greatly stimulated lateral grwth. Hwever, all levels f defliatin at midseasn (veraisn) r later had little r n effect n lateral elngatin (Table 4). A pssible explanatin fr this finding is that leaves at fruit-set, but nt a veraisn r later, prduce a substance (s) that inhibits lateral bud grwth. Upn remval f leaves, the lateral bud in the leaf axis may then be free t grw. Length f interndes was als reduced by defliatin at fruit-set, but nt at later dates; and this, t, may have ben due t reduced synthesis f sme substance(s), such as prmtr hrmnes, with lss in leaf area. Degradatin f inhibitrs, such as abscisic acid, culd als accunt fr these phenmena. LITERATURE CITED EFFECT OF DEFOLIATIONm64 1. Buttrse, M. S. The effect f reducing leaf area n the grwth f rts, stems, and berries f Grd grape vines. Vitis 5:455-64 (1966). 2. Buttrse, M. S. The effect f varying the berry number n Grd grape vines with cnstant leaf area. Vitis 7:299-302 (1968). 3. Fuller, R. D. The effect f time and rate f defliatin n grwth f Vitis vinifera L. grapes. M. S. Thesis, University f Califrnia, Davis. (1970). 4. Humphries, E. C. and G. N. Thrne. The effect f rt frmatin n phtsynthesis f detached leaves. Ann. Bt. N.S. 28:391-400 (1964). 5. Kliewer, W. M. Effect f time and severity f defliatin n grwth and cmpsitin f 'Thmpsn Seedless' grapes. Amer. J. Enl. Viticuit. 21:37-47 (1970). 6. Kliewer, W. M. and A. J. Antcliff. Influence f defliatin, leaf darkening, and cluster shading n the grwth and cmpsitin f Sultana grapes. Amer. J. Enl. Viticult. 21:26-36 (1970). 7. Kliewer, W. M. and C. S. Ough. The effect f leaf area and crp level n the cncentratin f amin acids and ttal nitrgen in 'Thmpsn Seedless' grapes. Vitis 9:196-206 (1970). 8. Kblet, W. The effect f leaf area n the yield and quality f grapes. Schweitz. Z. bst-u. Weinb. 105:624-7 (1969). 9. May, P., N. J. Shaulis, and A. J. Antcliff. The effect f cntrlled defliatin in the Sultana vine. Amer. J. Enl. Viticult. 20:237-50 (1969). 10. Olm, H. P. 1970: The year machine.havest came f age. Wines and Vines 52(2):30-1 (1970).