Fruit Crops: A Summary of Research 1998

Research Circular 299-99

Investigating the Relationship Between Vine Vigor and Berry Set of Field-Grown 'Seyval Blanc' Grapevines

Steven J. McArtney and David C. Ferree

Abstract

The number of clusters and shoots on mature field-grown grapevines was restricted soon after bud break to either 15/15, 15/30, 15/45, 30/30, 30/45 or 45/45 (cluster number/shoot number) in order to investigate the relationship between shoot vigor and berry set. There were no clear effects of shoot number per vine on either elongation rates or berry set within the range imposed in this study. Restricting the number of shoots per vine to 45 resulted in a 25 percent reduction in leaf area of individual shoots at bloom compared to vines with only 15 shoots. The reduced leaf area was related, at least in part, to a reduction in the number of leaves per shoot. Shoot elongation rates were higher for the two-week period following bloom than for either the period from bud break to bloom or from two to six weeks after bloom. Light transmission through the foliage canopy at bloom was inversely related to the number of shoots per vine. Leaf photosynthesis was the same for all treatments, suggesting that there was no compensation in photosynthesis even when the leaf area per shoot was reduced by 25 percent. Transpiration rates were positively related to the number of clusters per vine when measured under light saturation. Vine yields were positively related to cluster number whereas juice soluble solids and pH were negatively related to the number of clusters per vine. Petiole nitrogen was negatively related to the number of shoots per vine. The set of berries on the shoulder of individual clusters was a poor predictor of set on the whole cluster, accounting for only 34 percent of the total variation. These data suggest that when 45 shoots were retained per vine, which can be considered a commercial pruning intensity, the initial growth of individual shoots was limited by the supply of carbohydrates from storage reserves, as suggested by the reduction in leaf area per shoot at bloom, but this reduced leaf area was not a limiting factor for berry set.

Introduction

The relationship between vigor and fruiting potential has been extensively reviewed for apple (8), but similar information is lacking for grapevines. The number of fruit that set on apple trees is inversely related to the rate of vegetative development, particularly in the first few weeks following flowering. Grapevine inflorescences are a weak sink (12) and, presumably, the set of flowers is related positively to the supply of newly assimilated carbon from source leaves and negatively to the relative strength of competing sinks, i.e., other clusters on the same shoot and younger leaves at the shoot tip.

In the weeks that follow bud break, growth of grapevine shoots is dependant on the supply of remobilized carbohydrate reserves in cane, trunk, and root tissues. Buttrose (2) reported that four to five weeks of shoot growth were required before any net gain in dry weight of grapevine cuttings was observed, and cuttings made from a single node were retarded in growth rate from four to six weeks after bud break relative to cuttings grown from two-nodes. Winkler (19) demonstrated that leaf area at bloom determined the number of flowers that set and, subsequently, cluster weights at harvest. Taken together these results suggest that the growth rate of grapevine shoots is dependent on carbohydrate reserves in the cane tissues, and that shoots with a greater source leaf area at bloom will set more berries and yield higher. The situation for mature field-grown vines may be different, where the major reserve tissues for carbohydrates are the roots.

Overcropping and shading may both reduce the size of the pool of carbohydrate reserves in grapevines. Shading can also have a confounding effect on fruitfulness in the following season. May and Antcliff (13) found that when sunlight was reduced by about 70 percent for a four- to six-week period at the time of inflorescence initiation, there was a 20 to 40 percent reduction in the number of fruitful shoots in the following season. Altering the number of buds retained per vine at the time of winter pruning will alter the ratio of carbohydrate reserves relative to developing sinks (shoots), without altering the potential fruitfulness of the buds themselves. Williams (18) reported that when the number of shoots retained per vine was increased, both the leaf area per shoot and the mean size of primary shoot leaves were reduced. The growth rate of primary shoots, expressed on a growing-degree-day basis, on vines with only 52 shoots was more than double that for vines with 60 or 90 shoots.

Changes in leaf area may not result in a change in net carbon supply since rates of leaf photosynthesis can compensate for changes in leaf area. When leaf area was reduced by defoliation, photosynthesis of the remaining leaves increased (3, 11) or did not change (4). In explaining the lack of response, Candolfi-Vasconcelos et al. (4) proposed that a certain "degree of stress" originating from an unbalance in the source to sink ratio might be needed to trigger a compensatory response in photosynthesis

The growing shoot tip is the major sink for assimilated carbon during the period of cluster elongation on a grapevine shoot (9). In the first phase of berry growth, following cluster elongation, cells in the fruit are rapidly dividing (10) and the developing cluster becomes a major sink for assimilates relative to the shoot tip (15). There does not appear to be a clear relationship between the rate of shoot growth and berry set in the literature for the grapevine. Treatments that reduced the sink strength of developing shoots during the first growth stage, such as tipping (17), pinching and topping (6), and water stress (1), all reduced the number of berries set per cluster. However, May et al. (14) pruned vigorous Sultana vines to different bud numbers and found that berry number per bunch decreased as the number of buds per vine increased, suggesting the set of berries is reduced on rapidly growing shoots, and flowers are weaker sinks than the shoot tip during the period of berry set.

Low light levels can reduce the set of berries (7). Catechini and Palliotte (5) reported that PAR level in the region of the cluster was around 7 percent of ambient levels during flowering. In a growth chamber study, Roubelakis and Kliewer (16) found that percentage fruit set and ovule fertilization at 2,680 ft-c were three- and eight-fold greater, respectively, than at 750 ft-c.

The objective of this experiment was to explore the relationship between shoot growth rate and berry set on grapevines.

Materials and Methods

The number of shoots retained on mature field-grown Vitis vinifera L. Hybrid 'Seyval blanc' grapevines was restricted to either 15, 30, or 45 per vine when developing shoots were approximately 2 cm in length (May 20, 1996). Clusters were removed to leave the basal cluster on each shoot. There were three additional treatments (15 clusters/30 shoots; 15 clusters/45 shoots; 30 clusters/45 shoots) in order to separate the effects of shoot and cluster number per vine on shoot growth rate and berry set. Each of the six treatments was applied to six grapevines arranged in a randomized complete block design. Ten fruiting shoots per vine were selected on May 20, 1996. The length of each of these sample shoots was measured at bud break (May 20, 1996), bloom (June 18, 1996), two weeks after bloom (July 3, 1996), and six weeks after bloom (August 6, 1996), and the growth rate (mm.day^-1) between each of these dates calculated. The relationships between (i) shoot diameter (at the base), (ii) shoot length, or (iii) leaf number and total leaf area were assessed on a sample of 45 shoots destructively harvested from adjacent vines. Shoot length was used to predict leaf area per shoot for each of the sample shoots at bloom. Photosynthesis and transpiration were measured under light saturation at bloom on four fruiting mid-shoot leaves per vine using a portable infrared gas analyzer equipped with a 6.25 cm² leaf chamber (Analytical Development Co. model LCA2, Hoddesdon, England). Air-flow rate was regulated at 300 ml.min-1, and ambient CO₂ concentration was monitored periodically during each series of measurements. Light transmission (percent ambient) through the canopy was measured on June 24, 1996, by placing a 1 m line quantum sensor (LiCOR, Lincoln, Nebraska) under the foliage canopy of each vine in the north, south, east, and west quadrants. Berry set was estimated for the 10 sample clusters per vine as the number of berries, counted at harvest, per 100 flowers, counted at bloom. Flower counts were made on the shoulder of the cluster. If there were less than 60 flowers on the shoulder, then a count of flowers on the entire cluster was taken. Berry set on the shoulder was compared to that of the total cluster on a sample of 30 clusters. Yield and cluster number per vine were recorded at harvest, and fruit quality [soluble solids, pH, and titratable acidity (TA)] were measured on a random sample of 100 berries taken from the pooled fruit from the 10 sample clusters per vine. The nitrogen content of petioles was determined using the Kejldahl method on a sample taken at harvest.

Results and Discussion

Shoot growth rates were highest during the two weeks following bloom (Table 1), coincident with the period of maximum flower abscission. Slowest growth of shoots occurred in the period from two to four weeks after bloom. There were only minor effects of the treatments on shoot elongation rates during the period from bud break to bloom and from two to six weeks after bloom, but there were no effects due to treatment in the two-week period starting at bloom. Shoot elongation between bud break and bloom was less on vines with 30 clusters and 45 shoots compared with the other treatments (P < 0.05). Vines with 15 clusters and 45 shoots had faster shoot elongation rates during the period from two to six weeks after bloom compared to vines with 15 clusters and either 15 or 30 shoots.

Shoot length was a better predictor of leaf area per shoot than shoot diameter or leaf number. Eighty-four percent of the total variation could be explained by shoot length, compared to only 71 percent for both shoot diameter and leaf number (Figure 1). Leaf area per shoot at bloom, estimated from the regression relationship between shoot length and leaf area, was negatively related to the number of shoots per vine. Increasing the number of shoots per vine from 15 to 30 resulted in a 10 percent reduction of the leaf area per shoot, measured at bloom, whereas leaf area was reduced by an average of 25 percent when 45 shoots were retained per vine (Table 2). This reduction could be explained, at least in part, by a reduction in the number of leaves per shoot (Table 2). These data suggest that leaf appearance is more sensitive to a limitation in carbohydrate supply than shoot elongation.

Figure 1. Relationship between the diameter of a shoot at its base (A), shoot length (B), and leaf number per shoot (C) on total leaf area of Vitis vinifera L. Hybrid 'Seyval' grapevines (n=45).

There was no effect of treatment on berry set, measured as the number of berries that set per 100 flowers on the shoulder of each of 10 sample clusters per vine (Table 1). Berry set was around 50 percent for all treatments. Reducing the leaf area per shoot by 25 percent had no effect on berry set when there was only one cluster present on each shoot. The highest number of shoots per vine imposed in this study could be considered a conventional commercial treatment. Under a system of minimal pruning where greater numbers of shoots are retained per vine, one might expect to see more inhibition of growth of individual shoots and a parallel reduction in berry set. The authors observed poorer berry set on vines adjacent to those used in this study which carried as many as four clusters on a single shoot, suggesting that set may be reduced by competition between clusters on the same shoot.

Light transmission through the foliage canopy at bloom was related to shoot number per vine, transmission being higher on vines with fewer shoots (Table 2). Approximately 50 percent of ambient light was transmitted through the canopy on vines with 15 shoots, whereas transmission was an average of 37 and 29 percent of ambient for vines with 30 and 45 shoots respectively. Cluster number per vine had no effect on light transmission. Cartechini and Palliotti (5) reported much lower values for light transmission, finding that PAR levels measured at the cluster at bloom were only 7 percent of ambient. Considering that the authors found that 29 percent of the ambient light was transmitted beneath the foliage canopy on what they considered 'commercially' managed vines, then light levels at the cluster would have had a higher light level. Photosynthesis under light-saturated conditions (> 800 µmol.m^-2.s^-1) was not affected by either the number of clusters or shoots per vine (Table 2), suggesting there was no compensation and that perhaps even with 45 clusters and shoots, the vines were not under stress. Leaf transpiration was related to the number of clusters per vine, transpiration rates generally being lower on vines with fewer clusters.

The number of clusters per vine at harvest was fewer than was intended when the treatments were applied soon after bud break (Table 3). Vines that were intended to carry 15, 30, and 45 clusters in fact produced an average of 9.4, 23.1, and 37 clusters respectively. The authors believe that the major loss of clusters occurred soon after bloom as a result of damage to clusters during the counting process. Cluster number per vine was positively related to yield; however, vines with a greater leaf to fruit ratio (more shoots than clusters) did not produce larger clusters, suggesting that movement of assimilated carbon did not occur between shoots.

Fruit quality at harvest was affected by the treatments. The soluble-solids content of juice was inversely related to cluster number (Table 4). Fruit from vines with 15, 30, and 45 clusters had an average soluble-solids content of 18.0, 16.1, and 15.3 percent respectively. The ratio of clusters to shoots per vine had no effect on soluble-solids content. A similar trend was observed for juice pH; vines with only 15 clusters tended to have a higher juice pH (Table 4). There were no significant effects of the treatments on TA of juice, although the trend was for lower TAs of juice from vines with only 15 clusters. Increasing the number of vegetative shoots reduced the nitrogen content of petioles on vines with only 15 clusters. The number of clusters per vine did not affect the petiole nitrogen content (Table 4).

There was a poor relationship between the set of berries on the shoulder of individual grape clusters and the set of the entire cluster (Figure 2). Only 34 percent of the variation in total cluster berry set was explained by a linear relationship with the set of berries on the shoulder of the same cluster.

Figure 2. Relationship between set of berries on the shoulder of clusters of mature field-grown Vitis vinifera L. Hybrid 'Seyval' grapevines and berry set on the total cluster (n=29).

Conclusions

Increasing the number of shoots per vine did not have a clear effect on the rate of shoot elongation but did reduce the leaf area per shoot at bloom, at least in part by reducing leaf number, suggesting that the supply of carbohydrates from remobilized reserves to each shoot was limited and that leaf number was more sensitive than shoot elongation to this limitation. Despite a 25 percent reduction in the leaf area per shoot at bloom, berry set was unaffected. The data suggest that either (i) individual shoots are independent in their carbon economy and that even with a reduction of 25 percent there is still sufficient leaf area (current assimilates) to ensure optimal set of berries, or (ii) shoots are not independent in their carbon economy and the delivery of current assimilates from proximal vegetative shoots can compensate for a reduction in leaf area on flowering shoots. The authors found no evidence for compensation in the rate of photosynthesis when leaf area per shoot was reduced by 25 percent, suggesting that even with 45 clusters and shoots, vines were not under stress. In this study, the rate of shoot elongation was most rapid during the two weeks following bloom, coincident with the period of maximum flower abscission. During this period, the shoot tip is a major sink for newly assimilated carbon. This carbon is exported from the basal leaves on the shoot proximal to the developing cluster(s) (9). Set in the present study was high, with almost half of the flowers on each cluster developing into a berry. Perhaps in further studies the potential for variation in berry set due to imposed treatments can be enhanced by leaving additional clusters on each shoot so that the ratio of vegetative and reproductive sinks is reduced.

Literature Cited

1. Alexander, D. M. 1965. The effect of high temperature regimes or short periods of water stress on development of small fruiting Sultana vines. Austr. J. Agric. Res. 16: 817-823.
2. Buttrose, M. S. 1966. Use of carbohydrate reserves during growth from cuttings of a grapevine. Austr. J. Biol. Sci. 19:247-256.
3. Candolfi-Vasconcelos, M. C. and W. Koblet. 1991. Influence of partial defoliation on gas exchange parameters and chlorophyll content of field-grown grapevines. Mechanisms and limitation of the compensation capacity. Vitis 30:129-141.
4. Candolfi-Vasconcelos, M. C., W. Koblet, G. S. Howell, and W. Zweifel. 1994. Influence of defoliation, rootstock, training system, and leaf position on gas exchange of 'Pinot Noir' grapevines. Amer. J. Enol. Vitic. 45:173-180.
5. Cartechini, A. and A. Palliotti. 1995. Effect of shading on vine morphology and productivity and leaf gas exchange characteristics in grapevines in the field. Amer. J. Enol. Vitic. 46:227-234.
6. Coombe, B. G. 1959. Fruit set and development in seeded grape varieties as affected by defoliation, topping, girdling, and other treatments. Amer. J. Enol. Vitic. 10:85-100.
7. Ebadi, A., P. May, and B. G. Coombe. 1996. Effect of short-term temperature and shading on fruit set, seed, and berry development in model vines of V. vinifera cvs Chardonnay and Shiraz. Austr. J. Grape Wine Res. 2:2-9.
8. Forshey, C. G. and D. C. Elfving. 1989. The relationship between vegetative growth and fruiting in apple trees. Hortic. Rev. 11:229-287.
9. Hale, C. R. and R. V. Weaver. 1962. The effect of developmental stage on direction of translocation of photosynthate in Vitis vinifera. Hilgardia 33: 89-131.
10. Harris, J. M., P. E. Kreidemann, and J. V. Possingham. 1968. Anatomical aspects of grape berry development. Vitis 7:106-119.
11. Hofacker, W. 1978. Investigations on the photosynthesis of the vine. Influence of defoliation, topping, girdling, and removal of the grapes. Vitis 17:10-22.
12. Keller, M. and W. Koblet. 1994. Is carbon starvation rather than excessive nitrogen supply the cause of inflorescence necrosis in Vitis vinifera L.? Vitis 33:81-86.
13. May, P. and A. J. Antcliff. 1963. The effect of shading on fruitfulness and yield in the Sultana. J. Hortic. Sci. 38:85-94.
14. May, P., M. R. Sauer and P. B. Scholefield. 1973. Effects of various combinations of trellis, pruning, and rootstock on vigorous Sultana vines. Vitis 12:192-206.
15. Peterson, J. R. and R. E. Smart. 1975. Foliage removal effects on 'Shiraz' grapevines. Amer. J. Enol. Vitic. 26:119-124.
16. Roubolakis, K. A. and W. M. Kliewer. 1976. Influence of light intensity and growth regulators on fruit set and ovule fertilization in grape cultivars under low-temperature conditions. Amer. J. Enol. Vitic. 27:163-167.
17. Skene, K. G. M. 1969. A comparison of the effect of Cycocel and tipping on fruit set of Vitis vinifera L. Austr. J. Biol. Sci. 21:1305-1311.
18. Williams, L. E. 1987. Growth of 'Thompson Seedless' grapevines: I. Leaf area development and dry weight distribution. J. Amer. Soc. Hortic. Sci. 112:325-330.
19. Winkler, A. J. 1958. The relation of leaf area and climate to vine performance and grape quality. Amer. J. Enol. Vitic. 9:10-23.