Long-term Effects of Pruning Severity, Nodes per Bearing Unit, Training System, and Shoot JSHS 109(5):676-83 1984 Positioning on Yield and Quality of `Concord' Grapes

Yields on 'Concord' grape (Vitis labrusca L.) increased as pruning severity was decreased until the 6th and last year of this study, at which time the yields tended to equalize between the 30 + 10, 50 + 10, and 70 + 10 pruning treatments. By the last year, vines pruned to the 70 + 10 level produced fruit of unacceptable quality. When the 3-node spurs were shoot-positioned, their productivity was comparable to buds on the 6and 9-node canes, indicating the need for exposure to sunlight. The length of the bearing unit has little or no effect on fruit quality attributes. In general, shoot positioning increased yield, node productivity, the percentage of soluble solids, and lowered vine size throughout the study. Geneva Double Curtain (GDC) trained vines produced more fruit than the bilateral cordon (BC) trained vines. Fruit from GDC trained vines had a reduced percentage of soluble solids in 2 of the last 3 years, and tended to have a low pH. The most productive vines producing fruit of acceptable quality for the 6-year mean were the GDC trained, 50 + 10 pruned to 6-node bearing units, and shoot positioned. Vine vigor and vine size have been shown by early researchers (4, 21, 22) to determine the number of nodes that should be retained on 'Concord' grapes for optimum production and quality. Recently, it has been demonstrated that light pruning increases yield (3, 7, 9, 10, 13, 16, 18, 25, 28, 31, 32), but that excessively light pruning may reduce bud fruitfulness (3, 10, 16, 30) and fruit quality (3, 10, 16, 18, 23, 28, 31, 32). Several years of mechanical pruning without node adjustment has reduced bud fruitfulness and fruit quality (14, 15, 17). The number of nodes retained per cane or spur also affects grape yields. Basal buds are not as fruitful as others (6, 7, 11, 19, 20, 24) due to shading (25, 27). If shoots are positioned vertically downward, these lower nodes are exposed to increased light during the growing season and, consequently, become more productive (3, 25). Several training systems have been evaluated for 'Concord' grapes (l, 2, 3, 5, 8, 12, 16, 25, 26, 27, 29). In Arkansas, 'Concord' grapevines trained to the Geneva Double-Curtain System consistently produced larger yields than did vines trained to the bilateral cordon (3, 16) or Umbrella Kniffen (16) systems, and the yield increase from the Geneva Double Curtain system did not result in reduced quality (3, 16). Yet with the prospect of mechanized vine pruning (14, 15, 17), which requires cordon-trained vines, there is a need to evaluate cordon training of 'Concord' grapes further, and, in particular, to determine for them the optimum pruning severity and cane length and the effects of shoot positioning. This study examined the extended effects of pruning severity, nodes per bearing unit, training system, and shoot positioning on the yield and quality of 'Concord' grapes. Materials and Methods This study was initiated in 1973 in a 17-year-old, own-rooted nonirrigated 'Concord' vineyard at the Arkansas Agricultural Experiment Station, Fayetteville, and continued through 1979. Vine spacing was 2.4 m within the row and 3.1 m between rows. Treatments in a complete factorial design included: 1) 3 pruning severities; 30 + 10, 50 + 10, and 70 + 10 (30, 50, or 70 nodes retained for the 1st 454 g of dormant prunings and 10 additional nodes retained for each additional 454 g of prunings removed); 2) 3 levels of nodes/bearing unit; 3, 6, or 9 nodes per spur or cane; 3) 2 training systems, bilateral cordon (BC) or Geneva Double Curtain (GDC); and 4) 2 canopy positioning treatments; not positioned (NP) (shoots allowed to grow at random) or shoot positioned (SP) (shoots manually positioned vertically toward the vineyard floor). Shoot-positioning usually was required 3 times a year at about 2-week intervals, beginning at berry shatter. Prior to the study, all vines were spur-pruned (3 to 4 nodes in length) to a 30 + 10 pruning severity. A preliminary report (1st 2 years) of this study outlined the details of these treatments and was published in 1977 (3). Professor. Research Assistant. Received for publication 22 Feb. 1984. Published with the approval of the Director of the Arkansas Agr. Expt. Sta. The authors wish to thank the National Grape Co-operative Assn., Inc. for financial assistance in this research. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. All treatments were applied to the same plots each year. Each plot consisted of 5 vines and all treatments were replicated 3 times. Individual vine yields and pruning weights were determined. Three fruit samples were taken each year starting after veraison when the 50 + 10, bilateral cordon, nonpositioned, 6node cane plots had developed 12% soluble solids, and continuing at 7-10 day intervals. The last fruit samples were collected at harvest (Sept. 4, 2, 2, 7, 1 1, and 10 in years 1 through 6). Fruit samples, consisting of 3 whole basal clusters from each plot were frozen in polyethylene bags for subsequent analysis. Samples were thawed overnight at 2°C for analysis, and the number of berries per cluster and berry weight were determined. The fruit were blended at high speed for 15 sec in a blender and the percentage of soluble solids was determined on a Bausch and Lomb Abbe refractometer after filtering several drops of juice through 2 layers of Kim wipes. The samples then were heated for 1 hr at 85°, allowed to cool to about 40°, and the pulp was separated from the juice by squeezing through 2 layers of grade 50 cheesecloth. For color determination, a 5-m1 aliquot of juice was diluted to 100 ml with deionized water, centrifuged at 4000 rpm for 30 min, and the absorbance was determined at 520 nm on a Bausch and Lomb model 340 spectrophotometer. Another 5-ml portion of juice was diluted to 125 ml with deionized water, the pH determined, and acidity measured by titrating to pH 8.4 with 0.IN NaOH. Titratable acidity is reported as the percentage of tartaric acid. The data, by individual year and combined over all years, were subjected to factorial analyses of variance. Duncan's multiple range test at the 5% level was used to separate means of the main effects, and the least significant differences (LSD) was used to separate means of the significant interactions. Total yields, yield/node, pruning weight, production of soluble solids/ ha, berries per cluster, and berry weight are presented for every year of the study and for the 6-year mean. Since the results tended to be consistent across time. only the 6-year means are shown for the quality measures. The last year was selected because treatments had reached equilibrium by the 6th year of the study. The statistical analysis indicated that the majority of the significance can be explained by the main effects. The data, therefore, are presented as main effects, and only the relevant interactions are presented. Linear regression analysis was used to examine the relationship of acidity and color to the development of soluble solids. Table I . Main effects of pruning severity on the total yield, yield/node, pruning weight, and production of soluble solids/ha of `Concord' grapes for 6 years. Pruning Year Severity 1st 2nd 3 4 5 6th 6-year mean Yield (Mt/ha) 30 + 10 8.6 c' 12.1 b 3.1 6 17.4 c 14.6 b 18.8 a 12.4 c 50 + 10 11.0 b 13.9 b 5.3 a 19.5 b 16.8 ab 19..0 a 14.2 b 70 + 10 13.5 a 16.2 a 6.2 a 21.7 a 17.0 a 20.3 a 15.8 a Yield (g/node) 30 + 10 110 a 170 a 53 a 272 a 217 a 250 a 179 a 50 + 10 107 a 146 ab 67 a 221b 193 b 220 b 159 b 70 + 10 107a 140b 59a 198c 154c 186c 141 c Berries/cluster 30 + 10 41.0 a 34.4 a 20.5 b 44.8 a 35.3 a 45.6 a 36.9 a 50 + 10 38.9 a 34.5 a 20.9 a 43.7 a 33.0 b 42.3 b 35.5 b 70 + 10 39.7 a 33.1 a 22.4 a 42.2 a 31.4 b 3 9.8 b 34.8 b Berry weight (g) 30 + 10 3.59 a 2.82 a 2.93 a 2.94 a 3.02 a 2.71 a 3.00 a 50 + 10 3.51 ab 2.94 a 3.03 a 2.89 ab 3.00 a 2.88 a 3.04 a 70 + 10 3.42 b 2.91 a 2.91 a 2.78 b 2.94 a 2.63 b 2.93 b Pruning weight (kg/vine) 30 + 20 1.73 a 1.62 a 1.17 a 1.44 a 1.45 a 1.41 a 1.47 a 50 + 10 1.70 a 1.46 a 3.01 a 1.16 b 1.32 a 1.13 b 1.30 b 70 + 10 1.42 a 1.38 a 1.05 a 1.08 b 1.28 a 1.07 b 1.21 b Soluble solids (MT/ha) 30 + 10 1.35 c 2.01 b 0.50 b 2.49 b 2.23 a 2.92 a 1.92 c 50 + 10 1.74 b 2.16 b 0.86 a 2.74 ab 2.55 a 3.00 a 2.18 b 70 + 10 2.01 a 2.61 a 1.03 a 2.88 a 2.56 a 3.00 a 2.35 a Means within pruning severity and year separated by Duncan's multiple range test at the 5% level. Results and Discussion Pruning severity. In the 1st and 4th years of the study and across all years, each decrease in pruning severity resulted in increased yields (Table 1). The 70 + 10 pruning severity produced higher yields than the 30 + 10 severity for 5 of the 6 years. The unusually low yields in the 3rd year were due to late spring frosts which eliminated much of the crop. By the last year of the study, however, there were no differences in yield among any of the pruning severities. The equalization of yields by the last year can be explained partially by examining the yield components. Node fruitfulness (g yield/node) decreased as pruning severity decreased in the last 3 years of the study and for the 6-year mean (Table 1). Similar trends were noted in berries/ cluster, with significant reductions occurring on lightly pruned vines during the last 2 years of the study and for the 6-year mean (Table 1). The 70 + 10 pruning severity produced slightly smaller berries than 30 + 10 and 50 + 10 for the 1st, 4th, and 6th years and for the 6-year mean (Table 1). Vines pruned to the 50 + 10 and 70 10 severities were less vigorous than those pruned to 30 + 10 during 2 of the last 3 years and for the 6-year mean as indicated by smaller pruning weights (Table 1). The magnitude of pruning weight difference between 30 + 10 and 70 + 10 generally did not increase during the duration of the study, however, indicating no accumulative vigor-suppressing effect of continued light pruning. For the 1st 4 years of the study and for the 6-year mean, the production of soluble solids per hectare tended to increase as pruning severity decreased (Table 1). Yet there were no differences in the production of soluble solids per hectare due to the pruning severity by the last year of the study, which indicates an equilibrium of the total photosynthetic capacity of the vines may have been reached by the last year. The 70 + 10 pruning severity resulted in a lower percentage of soluble solids than the 50 + 10 and 30 + 10 pruning severities over all 6 years (Table 2). Fruit from vines pruned to the 70 + 10 severity did not meet the minimum requirements for the percentage of soluble solids (15%) established by the juice industry in the last year and for 2 other years (data not shown). Pruning severity did not affect fruit acidity during the study, but the 30 + 10 severity resulted in slightly higher fruit pH than 50 + 10 and 70 + 10 for the 6-year mean (Table 2). Pruning severity had a reverse effect on fruit pH during the short crop Table 2. Main effects of pruning severity, nodes/bearing unit, training system, and shoot positioning on the quality of 'Concord' grapes, 6-year means. Soluble Solids Acidity Color Main effect (%) (%tartaric) pH (abs. at 520nm) Pruning severity 30 + 10 15.6 a 0.81 a 3.65a 0.266a 50 + 10 15.6 a 0.80 a 3.61b 0.256a 70 + 10 15.1 b 0.81 a 3.62b 0.234b Nodes/bearing unit 3 15.5a 0.81a 3.64a 0.252a 6 15.3a 0.80ab 3.62a 0.249a 9 15.5a 0.79b 3.62a 0.255a Training system BC 15.5a 0.80a 3.65a 0.251a GDC 15.3a 0.80a 3.61b 0.253a Shoot positioning Not positioned 15.1b 0.81a 3.64a 0.244b Positioned 15.7a 0.80a 3.61b 0.260a Means within main effect separated by Duncan's multiple range test at the 5% level. of the 3rd year (data not shown). The 70 + 10 pruning severity produced fruit with poorer color quality (absorbance at 520 nm) than the 30 + 10 and the 50 + 10 for the 6-year mean (Table 2). When the rates of change in acidity and color were related to the development of soluble solids, interesting relationships were observed for the pruning treatments. As the pruning severity increased from 70 + 10 to 30 + 10, there was an increase in acidity at a given level of soluble solids for the 6-year mean (Fig. 1). This relationship was especially pronounced during the last year of the study. The. reduced acidity of fruit from lightly pruned vines may be due partly to the long time required for fruit on the vine to reach a given level of soluble solids. Acidity declines rapidly after veraison under the high maturation temperatures experienced in Arkansas. This relationship between soluble solids and color development showed a similar trend during the last year of the study. The juice of grapes from the 70 + 10 pruning treatment had inferior color compared to juice from the heavily pruned vines at a given level of soluble solids (Fig. 2). Even though the yields remained high on vines for the 70 + 10 pruning level for the entire 6 years, and adequate soluble solids may have been attained by delaying harvest, quality as determined by acidity and color were adversely affected. Nodes/bearing unit. The main effects of nodes per bearing unit indicate that the 3 node spurs produced lower yields than the 6and 9-node canes for the 1st year of the study, and tended to produce lower yields during the remainder of the study as indicated by the 6-year mean (Table 3). The 9-node canes had greater node productivity (g yield/node) than 3-node spurs and 6-node canes in the last year of the study, and the 6-year mean shows that node productivity increased with each increase in cane length (Table 3). The 9-node canes also produced larger clusters (berries/cluster) than did the 3-node spurs in the last year of the study, and for the 6-year mean (Table 3). These results are in agreement with Partridge (21, 22) who reported that the 4th and 5th nodes are the most productive nodes on 'Concord' canes. Berry weight was not affected by nodes/bearing unit (Table 3). Pruning to 3-node spurs resulted in increased vine vigor as compared to pruning to 9-node canes for 4 of the years, and the 6-year mean shows that vine vigor decreased with increasing cane length (Table 3). The 3-node spurs tended to have lower production of soluble solids/hectare than did the 9node canes as indicated by the 6-year mean (Table 3). The percentage of soluble solids, pH, and color were not affected by the number of nodes left on the cane, but the 3-node spurs tended to produce fruit with slightly higher acidity than the 9-node canes (Table 2). Table 3. Main effects of nodes/bearing unit on the total yield, yield/ node, pruning weight, and production of soluble solids/ha of 'Concord' grapes for 6 years. Nodes/ Year Bearing 6-year Unit 1st 2 3rd 4th 5 6th mean Yield (Mt/ha) 3 9.0 b 13.6 a 5.1a 18.7 a 15.6a 18.4a 13.4b 6 11.4 a 13.9 a 4.7 a 19.8 a 16.1a 19.7a 14.4a 9 12.7 a 14.6 a 4.8 a 20.0 a 15.7a 20.0a 14.6a Yield (g/node) 3 85 6 139 b 65 a 220a 179a 201b 148c 6 113 a 148 ab 56a 235a 194a 217b 160b 9 127 a 170 a 57 a 237 a 191 a 238a 170a Berries/cluster 3 48.3 a 34.1 a 20.8a 42.5a 31.36 40.7b 35.0b 6 38.9 a 33.9 a 21.1 a 44.2 a 34.4 a 42.8ab 35.9ab 9 40.4 a 34.1 a22.0 a 43.9 a 33.9 a 44.1a 36.4a Berry weight(g) 3 3.52 a 2.94 a2.95 a 2.90 a 3.09 a 2.76 a 3.03a 6 3.51 a 2.86 a 2.96a 2.88a 2.87b 2.71 a 2.97a 9 3.49 a 2.87 a 2.95 a 2.84 a 3.00 ab 2.75 a 2.98a Pruning weight (kg/vin) 3 2.00 a 1.74 a 1.05 a 1.27 a 1.54 a 1.43 a 1.50a 6 1.44 b 1.47 b 1.09 a 1.24 a 1.40 ab 1.26 a 1.32b 9 1.42 6 1. 24 b 1.10 a 1.17 a 1.12 b 0.92 b 1.16c Soluble solids (MT/ha) 3 1.40 b 2.19 a 0.83a 2.58a 2.44a 2.85a 2.05a 6 1.77 a 2.19 a 0.77 a 2.75 a 2.54 a 2.98 a 2.17ab 9 1.92 a 2.41 a 0.79 a 2.78 a 2.37 a 3.08 a 2.22a Means within nodes/bearing unit and year separated by Duncan's multiple range test at the 5% level. Training system. Training system did not affect yield of vines for the 1st 3 years of the study, but vines on the GDC system produced a higher yield than those on the BC system for the last 3 years and for the 6-year mean (Table 4). The large yields on the GDC system during the last 3 years were probably a result of improved node fruitfulness on the GDC system (Table 4). The GDC system resulted in more berries/cluster than the BC system during the last year of the study and for the 6-year mean, but vines on the GDC system produced larger berries only in the last year of the study (Table 4). There were no differences in the vine vigor between the GDC and BC system with the exception of the 5th year, when the GDC system produced increased vine growth (Table 4). The production of soluble solids per hectare was greater for vines on the GDC system than those on the BC system for 2 of the last 3 years, and for the 6-year mean (Table 4). The vines on the GDC system produced fruit with a lower percentage of soluble solids than the BC system for 2 of the last 3 years (data not shown), but there were no differences in the percentage of soluble solids between training systems for the 6-year mean (Table 2). Acidity and color quality were the same for juice from both training systems during the study, but the GDC system resulted in slightly reduced juice pH for the 6-year mean (Table 2). Although vines on the GDC training system generally are considered to be more productive than those on BC in this study, the high yields did not result in significant overall juice quality reductions. Shoot-positioning. Yield and node productivity were increased by shoot positioning in every year except the 1st (Table5). Shoot positioning significantly increased cluster size in only one year, but tended to increase cluster size as shown by the 6-year mean (Table 5). Berry weight was not affected by shoot positioning in any year. Shoot positioning lowered pruning weight in all years except in the 1st year (Table 5). The production of soluble solids per hectare was increased by shoot positioning in 4 of the years, and for the 6-year mean (Table 5). Shoot positioning increased the percentage of soluble solids and color quality and slightly lowered the pH of grapes at harvest for the 6-year mean, but fruit acidity was not affected by shoot positioning (Table 2). A regression analysis showing the relationship between soluble solids development and acidity changes showed that there was a slightly reduced acidity at a given soluble solids level for fruit from the nonpositioned vines for the 6-year mean and during the final year of the study (Fig. 3). The reduced acidity of fruit from nonpositioned vines can be explained partially as additional time required to reach a given level of soluble solids, and the relationship between postveraison acid loss and the high maturation temperature in Arkansas. Fruit from positioned and nonpositioned vines were similar in color at a given soluble solids (data not shown). Interactive and combination effects. A significant interaction between nodes per bearing unit and shoot positioning for the 6-year mean shows the advantage of shoot positioning 3-node spurs and 6-node canes to increase total yield (Fig. 4). This yield increase was a result of increased node productivity (g fruit/node) of the shoot positioned vines. Shoot positioning had little effect on yield (per hectare or per node) when vines were pruned to 9-node canes. Pruning to the long canes effectively reduces the extent of shading occurring along the cordon and thus shoot-positioning is not beneficial. Shoot-positioning vines pruned to short spurs results in more productive basal buds due to improved exposure to sunlight. Increasing the productivity of basal nodes by shoot-positioning is in agreement with Shaulis et al. (27). Pruning severity and shoot positioning produced a significant interaction for yield/node, indicating the tremendous increase in node productivity obtained by shoot-positioning vines pruned to 30 + 10 (Fig. 5). This response was due to reduced shading of nodes on these vigorous vines. Several interactions that were significant during the 1st 2 years of the study (1974 and 1975) and previously published (3) were not significant during the remaining years of the study or for the 6-year mean. These interactions included a reduction in yield of shoot positioned vines pruned to 3and 6-node spurs in the 1 st year. This reduction was probably due to the mechanical damage caused by the initial shoot-positioning process, since in the initial year all bearing units of the shoot positioned vines were not selected from the lower 180° of the cordons (3). The interactive effects of pruning severity x training system and pruning severity x shoot-positioning on fruit yield/kg of prunings were significant in the 1st 2 years of the study (3), but not during the remaining years of the study (data not shown).