Initial growth and fruiting of Summit sweet cherry (Prunus avium) on five rootstocks

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1 New Zealand Journal of Crop and Horticultural Science ISSN: (Print) (Online) Journal homepage: Initial growth and fruiting of Summit sweet cherry (Prunus avium) on five rootstocks A. Santos, R. Santos Ribeiro, J. Cavalheiro, V. Cordeiro & J. L. Lousada To cite this article: A. Santos, R. Santos Ribeiro, J. Cavalheiro, V. Cordeiro & J. L. Lousada (2006) Initial growth and fruiting of Summit sweet cherry (Prunusavium) on five rootstocks, New Zealand Journal of Crop and Horticultural Science, 34:3, , DOI: / To link to this article: Published online: 22 Mar Submit your article to this journal Article views: 715 Citing articles: 5 View citing articles Full Terms & Conditions of access and use can be found at

2 New Zealand Journal of Crop and Horticultural Science, 2006, Vol. 34: /06/ The Royal Society of New Zealand 2006 '269' Initial growth and fruiting of 'Summit' sweet cherry (Prunus avium) on five rootstocks A. SANTOS R. SANTOS-RIBEIRO J. CAVALHEIRO Departamento de Fitotecnia CECEA Universidade de Trás-os-Montes e Alto Douro Ap. 1013, Vila Real, Portugal asantos@utad.pt jtcc@utad.pt V. CORDEIRO DRATM Direcçào Regional de Agricultura de Trás-os-Montes CETQ Centro Experimental da Terra Quente Quinta do Valongo Carvalhais, MDL, Portugal victor.cordeiro@dratm.min-agricultura.pt J.-L. LOUSADA Departamento de Florestal CEGE Universidade de Trás-os-Montes e Alto Douro Ap. 1013, Vila Real, Portugal jlousada@utad.pt Abstract The sweet cherry (Prunus avium) cultivar 'Summit' still fits the standard of excellence for its typical characteristics, including large fruit size and cordate shape. This study was undertaken in Vila Real, northern Portugal, with 'Summit' scions raised in a nursery on five rootstocks. The orchard trials were set up in 1999, and tree growth, yield, and fruit size were monitored up to the 6th leaf. At this phase, the rootstock trunk cross-sectional areas (TCSAs) for Maxma 14, Cab 11E, Edabriz, and Gisela 5 were 79.7%, 60.2%, 37.9%, and 29.3% of that of Mazzard, respectively. Cumulative yield was higher on Gisela 5, but it did not differ significantly from Cab 11E Maxma 14, Edabriz, and P. avium attained only 56%, 50%, and 36% of H05125; Online publication date 25 August 2006 Received 31 October 2005; accepted 14 July 2006 Gisela 5 cumulative yield per tree, respectively. This latter rootstock also induced higher cumulative yield efficiency when compared with the other rootstocks. Average fruit weight varied significantly according to year, rootstock, and year rootstock interaction, which accounted for 62.6%, 13.2%, and 19.1% of the total variation, respectively. In 2002, it was Gisela 5 that permitted the cultivar to bear the best-sized fruits (9.8g), but in 2003 (6th leaf) this rootstock produced the lowest sized fruits(10.2g). Conversely, on Edabriz, Cab 11E, and P. avium average fruit weight increased 29%, 26%, and 24%, respectively. Trees on Gisela 5 had 5.6 leaves (190 cm 2 ) per fruit, whereas on Edabriz, Cab 11E, and P. avium they had 1.6, 2.3, and 6.4 times that value, respectively. Gisela 5 and Edabriz were very efficient in controlling vigour, having induced precocity and high cumulative yield efficiency. Leaf area/fruit ratio, however, limited fruit growth on Gisela 5, where initial high productivities demand appropriate tree nutrition to allow complete fruit, leaf, and limb growth and development on the current and subsequent season. Cab 11E was not so precocious, but proved to be productive and induced the best fruit growth. Suitable cultural practices must be adopted to fit rootstock requirements to optimise the balance between yield, fruit size, and economic value, especially for the most dwarfing. Keywords Gisela 5; Tabel Edabriz; Maxma 14; Cab 11E; dwarfing; productivity; fruit weight; leaf area/fruit INTRODUCTION The sweet cherry (Prunus avium L. ) harvesting period is placed in an advantageous position in the market, as consumers are eager for fresh fruit at that time of the year. Sweet cherries are also reputed for their health benefits, and their organoleptic characteristics combined with their excellent appearance add to their attractiveness. The increasing consumer demand for sweet cherries and the recent availability of new dwarfing rootstocks have motivated significant

3 270 New Zealand Journal of Crop and Horticultural Science, 2006, Vol. 34 efficiency improvements on the grower's activity, by overcoming inefficiencies associated with large tree size and the long establishment period before first fruiting. Additionally, sweet cherry is a delicate fruit that must be harvested by hand, and smaller trees are able to be almost completely hand-picked, which reduces cropping risks and charges significantly. Ystaas & Frøynes (1998) consider that the cultivar recommended for commercial production should be selected for the large size, attractive appearance, consistent high productivity, and good flavour of its fruits. Valuable attributes are also fruit resistance to rain-induced cracking, good firmness to resist bruising caused during harvest and handling operations, storage ability, and maintenance of quality during marketing. Cultivar 'Summit' is still a standard of excellence for its large fruit size (Kappel & Lane 1998), its characteristic cordate shape, glossy skin (Lichou et al. 1990), and taste qualities that determine the consumer's preference. The adequate choice of the rootstock is vital for the intensification of the production of 'Summit' cherries, since it is a vigorous cultivar, of erect growth, low spreading, with narrow crotch angles, and is slow to start bearing fruit. Rootstocks and budding height can influence this cultivar's vigour (Santos et al. 2004). Webster (1995) also emphasises the effect of rootstock upon growth habit, precocity, and abundance of scion flowering and fruiting, as well as yield efficiency. Gonçalves et al. (2005) observed, on the trees of this trial, that the rootstock genotype influences water relations, leaf gas exchange, chlorophyll afluorescence,canopy light transmittance, leaf photosynthetic pigments, metabolites, and fruit quality indices, although the latter two are mainly dependent from the cultivar genotype. Thedwarfing rootstocks confer several advantageous traits besides vigour control, including precocious fruiting and high productivity. However, smaller tree stature and higher density orchards are becoming common as the experience in crop load management on highly productive and vigour-controlling rootstocks increases (Lang & Ophardt 2000; Gutzwiler & Lang 2001; lang 2005; lauri & Claverie 2005), giving rise to more competitive farming. Dwarfed trees have lower ratios of leaves/fruit, and their architecture facilitates the even distribution of light throughout the canopy (Lang 2000), favouring the photosynthetic efficiency of the tree. It is nevertheless essential to adjust the number of fruits to the available adjacent leaf area, to supply enough photosynthetic carbon to achieve marketable fruit size. Although fruit growth in the developing and the previous-year shoots is not restricted as the ratio of leaves/fruit is non-limiting, the same is not true for the clusters, where the associated photosynthetic area frequently becomes limiting to fruit development (Roper et al. 1987; Atkinson et al. 2001; Ayala 2004). Loeschter et al. (1986) verified that the spurs are unable to supply more than two or three fruits, and Whiting (2001) observed that there is the need of a cm 2 leaf area to bestow an optimum balance between fruit quality and vegetative growth. Ayala (2004) found that a cm 2 ratio of leaf area/fruit indicates a persistent source limitation during fruit development. This paper aims to evaluate sweet cherry cultivar 'Summit' growth and productivity during the first 6 years of scion life when grafted onto rootstocks of different vigour, and their impact on fruit size. MATERIALS AND METHODS Climatic conditions and soil The study was carried out in an experimental orchard located in Vila Real, northern Portugal (41 27 N; 7 33 W) at 470m a.s.l. Local climatic conditions demand irrigation, usually between May and September, and so a drip irrigation system was activated for 3 h per day during these months, and 4 h per day during late spring and summer. Drippers were in line, 1 m apart, with a 4 litre h 1 flow rate. The soil was a deep (>100cm) sandy loam Distric Aric Anthrosol (FAO, UNESCO 1988), acid (ph 5.6), with high content of fine sand ( mm), high K 2 O content ( mg kg 1 ), medium P 2 o 5 ( mg kg 1 ), and low organic matter level Trial set up and management In September 1997, 'Summit' sweet cherry was chip-budded on five rootstocks: Edabriz (P. cerasus), Gisela 5 (P. cerasus P. canescens), Maxma 14 (P. mahaleb P. avium), Cab 11E (P. cerasus), and P. avium (Mazzard). The experiment was established in March The distance between the rows was 5.5 m, and the space between the plants along each row was chosen according to the expected relative vigour of the rootstock, as follows: 3, 4, 4.5, 5, and 5.5 m for plants on Edabriz, Gisela 5, Maxma 14, Cab 11E, and P. avium rootstocks, respectively. These spacings did not cause competition between canopies, as the trees did not fill their allocated space. Trees were

4 Santos et al. Productivity and value of 'Summit' sweet cherry 271 Fig. 1 Trunk cross-sectional area (TCSA) growing patterns of 'Summit' sweet cherry (Prunus avium) on different rootstocks by the end of the 6th year. Measurements on the rootstock, 5 cm above soil line. Mean values where the vertical bars represent standard errors (n = 12). CM X (ci CO o ; 175; 150; 12). IOO; 75; 0 Maxma14 / O A Prunus avium Cab11E / I Edabriz / / Gisela 5 / TZ^s^ T 25; 3 4 Tree age (years) allowed to grow freely, according to their natural predisposition. The experimental design was a split-split plot in randomised blocks, with two replications and two plants per experimental unit. The main plots were used for the rootstocks, the subplots for the cultivars, and three budding heights were taken as sub-subplots. In this study, sub-subplots were considered together, allowing 6 replications of each experimental unit, as Santos et al. (2004) found that only 4.1% was accountable to budding height effects. The field trial was minimally managed, the in-row soil kept free from weeds by herbicide sprayings, and appropriate fertilisation and irrigation were applied. Measurements and data analysis This study was carried out on cultivar 'Summit', up to the 6th leaf of scion life ( ). Trunk diameters were taken 5 cm above the soil line on the rootstock, in the nursery and every year onwards, and then trunk cross-sectional areas (TCSA) were calculated. In 2003 (6th leaf), tree height was measured, and canopy projection area on ground and tree canopy volume were calculated for all the trees. Canopy projection area was taken by measuring the area inside the line of projection of the largest crown diameter on the soil. The tree foliar area was calculated in October by counting the total number of leaves on one tree from each replication plot the reference tree. Five samples of 30 leaves were drawn from all the leaves of each reference tree, and individual leaf area was measured in a Li-Cor, LI 3100 device. The total leaf area of each reference tree was calculated by multiplying the total number of leaves by the average leaf area. Foliage density was assessed through five independent visual estimates based on the size of the reference tree. From the 4th to the 6th leaf ( ), total tree yield was examined and productivity indexes calculated: cumulative production (kg/tree); TCSA (kg cm 2 ); canopy projection area (kg m 2 ); and canopy volume (kg m 3 ). At the 5th and 6th leaf, on harvesting date, two samples of 15 fruits (in 2002) and three samples of 20 fruits (in 2003) from Ebabriz, Gisela 5, Cab 11E, and P. avium were picked and weighed. The data analysis followed the experimental design, and SuperANOVA (Abacus Concepts, Inc. 1991) was used to carry out the statistical analysis. Each selected variable was examined to compare the effects of the rootstock concerning tree growth, fruit yield, and fruit weight. The data analysis relative to fruit weight was performed as a 2-way factorial with 2 years and four rootstocks. Duncan's multiple range test at the 5% level was used to statistically evaluate different means. RESULTS Tree growth Trunk cross-sectional area differences were apparent, particularly after the 3rd leaf (Fig. 1). At the end of the 6th leaf, rootstock TCSAs for Maxma 14 and Cab 11E were 79.7% and 60.2% of Mazzard,

5 272 New Zealand Journal of Crop and Horticultural Science, 2006, Vol. 34 respectively. The TCSA of the scions increased less on the dwarfing rootstocks, reaching 37.9% on Edabriz and 29.3% on Gisela 5, when compared with P. avium. Trunk cross-sectional area is the most common method for estimating tree size (Webster 1995), since tree crown weight is closely related to trunk girth (Pearce 1952). Santos et al. (2004) also found a significant correlation between total tree length growth and TCSA. However, there are other growing parameters (Table 1 ) that allow for a better assessment of the implications rootstock has on the growth of the trees at the 6th leaf. When comparing growth in height of the trees on P. avium with that on other rootstocks, a significant variation was observed, ranging from 92% in Cab 11E to 61% in Edabriz. Trees on Edabriz and Gisela 5 reached similar height. Canopy projection area was also found to differ (P < 0.05) among the most vigorous trees (in Cab 1 1E and P. avium), the semi-vigorous (in Maxma 14), and the most dwarfed (in Gisela 5 and Edabriz). The plants on Maxma 14, Gisela 5, and Edabriz only reached 41%, 34%, and 20% of the canopy volume of those on P. avium. Rootstock Gisela 5 had the smallest total leaf area (Table 1). Trees on Edabriz, Maxma 14, Cab 11E, and P. avium, produced 1.5,2.3,3.3, and 4.4 times more leaf area than those on Gisela 5, respectively. Production and productivity 'Summit' trees started producing at the 4th leaf, with production varying between rootstocks. Of the tested rootstocks, Gisela 5 induced more precocity the production was c. 1 kg per tree at as early as the 4th leaf (Fig. 2). At the 5th leaf, production improved substantially, mostly in the trees on Gisela 5 (5.2kg/tree). In the following year, production rose dramatically in all rootstocks, and it was the scions on Cab 11E that produced higher yield per tree (9 kg). The cumulative yield from the 4th to the 6th leaf (Table 2) shows Gisela 5 as the rootstock with the highest yield accumulation as much as 12.6 kg/ tree. However, this value does not differ (P > 0.05) from those of the trees on Cab 11E. Maxma 14, Edabriz, and P. avium, produced only 56%, 50%, and 36%, respectively. Considering that production per tree can be a misleading parameter for fertility, because of the influence of tree size, the cumulative yield was also determined by cm 2 TCSA, by m 2 of canopy projection area, and by m 3 of canopy volume. Table 2 shows that Gisela 5 had the highest cumulative yield efficiency, and differed significantly from the other rootstocks; however, in the cumulative production by m 2 of canopy projection area, it did not differ from Edabriz. P. avium was the rootstock that promoted the lowest cumulative yield efficiency of 'Summit' up to the 6th growing season. Taking Gisela 5 as a reference, Mazzard reached only 11% of its cumulative yield per cm 2 TCSA and per m 3 of canopy, and 21% of its cumulative yield per m 2 of canopy projection. Fruit weight Average 'Summit' cherry weight varied significantly with year, rootstock, and year rootstock interaction, as shown in the ANOVA on Table 3. These factors were responsible for c. 95% of the individual fruit weight variance, each corresponding to a different value: 62.6% to year, 13.2% to rootstock, and 19.6% to the year rootstock interaction. The average weight of fruits picked in 2003 ( 11.0 g) was 21 % higher than of those picked in 2002 (8.7 g). Concerning rootstocks, it was the scions on Cab 11E that raised the heaviest fruits (10.9 g), but their weight did not differ much from those on P. avium. As for dwarfing rootstocks, the average fruit weights were quite low up to 10.0 g on Gisela 5 and only 9.3 g on Edabriz. Table 1 Tree height, canopy projection area, canopy volume and total leaf area of 'Summit' sweet cherry (Prunus avium) trees by rootstock at the end of the 6th scion growing season. Mean ± SD (n = 12). Values with the same letter are not significantly different at P 0.05 (Duncan's multiple range test). Rootstock Tree height (m) Projection (m 2 ) Canopy Volume (m 3 ) Leaf area (m 2 ) Edabriz Gisela 5 Maxma 14 Cab 11E P. avium 3.33±0.34a 3.42±0.49a 4.59±0.40b 4.98±0.16c 5.42±0.29d 1.77±0.62a 2.81±0.88b 2.17±0.57ab 4.34±0.83c 4.58±0.68c 1.51±0.60a 2.51±0.93ab 3.07±0.81b 6.39±1.32c 7.56±1.49c 16.53±2.34b 11.07±1.30a 25.66±1.49c 36.10±1.18d 48.38±1.63e

6 Santos et al. Productivity and value of 'Summit' sweet cherry 273 Fig. 2 Fruit yield per 'Summit' sweet cherry (Prunus avium) tree onto different rootstocks from the 4th to the 6th scion growing season. vertical bars represent standard errors (n = 12) o> per tree 2 4- Cab 11E El Edabriz H Gisela 5 H Maxma 14 Prunus avium T P I Ti i9 1 T - 2- o- Iiri 1 Tree age (years) Table 2 Effect of the rootstock on cumulative yield efficiency on ' Summit' sweet cherry (Prunus avium) trees on the first three production years ( ). Mean ± SD (n = 12). Values with the same letter are not significantly different at P 0.05 (Duncan's multiple range test). (TCSA, trunk cross-sectional area.) Rootstock Cumulative yield (kg/tree) kg cm- 2 TCSA Cumulative yield efficiency kg m 2 soil kg m 3 canopy Edabriz Gisela 5 Maxma 14 Cab 11E P. avium 6.29±0.77ab 12.62±3.66c 7.07±2.69ab 9.95±3.69bc 4.55±1.11a 0.085±21b 0.208±48c 0.045±17ab 0.080±24b 0.023±90a 4.15±2.25cd 4.99±2.17d 3.35±1.26bc 2.30±0.71ab 1.03±0.37a 4.94±2.72c 6.01±3.48d 2.35±0.84b 1.55±0.41ab 0.65±0.28a Table 3 ANOVA of 'Summit' sweet cherry (Prunus avium) fruit weight at the 5th and at the 6th growing seasons. Source of variation d.f. MS F(sig.) Variance comp. (%) Year (A) Rootstock (R) A R Residual (P<0.001) 32.1 (P<0.001) 23.6 (P<0.001) Fruit weight by rootstock can be observed on Fig. 3. At the 5th leaf, average weight per fruit was low in all rootstocks except Gisela 5, which bore fruits of 9.8 g. On the following year, the fruits grown on this rootstock had similar size but those of Edabriz, Cab 11e, and P. avium had an average size increase of 29%, 26%, and 24%, respectively. Regarding tree yield per rootstock in 2002 (Fig. 2), Gisela 5 promoted more and generally larger fruits (Fig. 3); this could have caused plant growth to be slower than on other rootstocks (Fig. 1). DISCUSSION TYee growth and productivity Under our experimental conditions, ' Summit' growth suffered reductions of 20% and 40% in TCSA when grafted on Maxma 14 and Cab 11E, respectively, compared with P. avium. This is in accordance with Edin & Tronel (1988), who mention vigour reductions of Maxma 14 ranging between 20% and 50%, depending on the cultivar. Furthermore, Saunier et al. (1998) add that this rootstock induces

7 274 New Zealand Journal of Crop and Horticultural Science, 2006, Vol " I 9 '5 O of leaves per fruit ro co 4^ en o o o o 10- T Gisela 5 Edabriz P. avium Cab 11E Rootstock Fig. 3 Average fruit size of ' Summit' sweet cherry (Prunus avium) by rootstock, at the 5th and 6th leaves. Mean values where the vertical bars represent standard errors (n = 30, 2002; n = 60, 2003). o- Edabriz Gisela 5 Cab11E P. avium Rootstock Fig. 5 Number of leaves per fruit on 'Summit' sweet cherry (Prunus avium) at the 6th leaf by rootstock. Mean values where the vertical bars represent standard errors (n = 12). E "5 >. Q. O <0 ü 10 1 y = x R 2 = Cab11E *. 4 - P. avium Gisela 5 Maxma Edabriz Leaf area (m 2 ) Fig. 4 Correlation between total leaf area and canopy volume of 'Summit' sweet cherry (Prunus avium) at the 6th scion growing season. good development during the first years, but not so good in adult trees, since it only allows for 60-70% of the vigour on F12-1. Compared with the other rootstocks (Maxma 14, Edabriz, and Gisela 5), tree height, canopy volume, canopy projection, and total leaf area were significantly higher on Cab 11E and P. avium (Table 1). As for Edabriz, the TCSA reduction at the 6th leaf was of c. 60% when compared with P. avium. This is in accordance to Edin (1989) who states that Edabriz can cause a diameter reduction of 40-70% when compared with F12-1, therefore being considered a dwarfing rootstock. Edabriz was the rootstock that originated, in the 'Summit' cultivar, lower height, canopy projection, and volume. Nevertheless, the difference recorded in relation to Gisela 5 was not significant except for the canopy projection parameter. Gisela 5 is also regarded as dwarfing by Walther & Franken-Bembenek (1998), who recorded canopy volume reductions of 33% in relation to F12-1 at the 7th leaf, and of 55% at the 9th leaf. However, the vigour reduction obtained under our experimental conditions concerning P. avium was rather intense as much as 70% of the TCSA, and 67% of the canopy volume. It is possible that the lower growth obtained with Gisela 5 could be attributable to the origin of this rootstock areas whose climate is not similar to the Mediterranean conditions of our experimental locations. Scion canopy volumes on Gisela 5 and Maxma 14 were not significantly different, but this latter rootstock promoted slimmer canopies and stronger

8 Santos et al. Productivity and value of 'Summit' sweet cherry 275 growth in height, which entails lower labour efficiency and higher management costs. Conversely, Gisela 5 is prone to change the cherry cultivar morphology crown architecture, and induce a more spreading and open growth habit (Perry et al. 1998; Saunier et al. 1998). Comparing total leaf area with canopy volume, Edabriz and Maxma 14 cause higher leaf density for unit of volume (Fig. 4). However, when analysing individual behaviour by rootstock, this interdependence of factors varies greatly from rootstock to rootstock: it is strong on Cab 11E (R 2 = 0.775), Edabriz (R 2 = 0.721), and Gisela 5 (R 2 = 0.457), but not in Maxma 14 (R 2 = 0.086) nor P. avium (R 2 = 0.051). Our results also emphasise the precocity and the excellent productivity of 'Summit' when grafted onto Gisela 5. On this rootstock, the accumulated yield per tree ( ) was c. 2.8% greater than that on P. avium, and the cumulative yield efficiency was higher than that observed on the other tested rootstocks (Table 2). When comparing F12-1 and Gisela 5, under Norwegian conditions, Ystaas &Frøynes (1996) found that the scion yield efficiency on the latter rootstock was 3 times higher, and Vestergaard (1996) refers to 4-7 times as much in Germany. In our experimental conditions, Gisela 5 outperformed P. avium, with 9.0, 4.8, and 9.2 times higher cumulative yield efficiency concerning TCSA, canopy projection, and canopy volume, respectively. In relation to Edabriz, Edin (1993) states that it confers very good precocity and high yielding capacity as it induces higher density of spurs and flowers. However, by the 6th growing season under our experimental conditions, Gisela 5 outperformed Edabriz too, with a 2.4 times higher cumulative yield efficiency concerning TCSA (Table 2). Hilsendegen (2005) also obtained higher productivities of 'Hedelfinger' and 'Regina' on Gisela 5 than on Edabriz at the 4th leaf, as did Charlot et al. (2005) with 'Summit' at the 10th leaf, although the 5th to 10th leaf cumulative yield had been 1.2 times higher on Edabriz under French conditions. Although invigorating rootstocks led to improved water status and high photosynthetic capacity (Santos & Moutinho-Pereira 2004; Gonçalves et al. 2005), limited carbon uptake did not necessarily reduce fruit yields on dwarfing rootstocks. Scions on dwarfing rootstocks differentiate more flower buds and flowers than on invigorating rootstocks. Maguylo (2003), working on the 'Hedelfinger' cultivar grafted onto Gisela 5, observed about four reproductive buds and flowers per spur, whereas on Mazzard this cultivar originated only 0.4. Factors affecting fruit weight The ANOVA of our data showed year and rootstock as the main factors influencing fruit weight. The effect of dwarfing rootstocks on fruit weight was indirect as it slowed limb growth rate and enhanced flower differentiation. Thus, the leaf area/fruit ratio was reduced, and affected directly fruit size. It was on Cab 1 1E that the cultivar bore the heaviest fruits, though the weight did not differ significantly from those on P. avium. De Salvador et al. (2005) also observed better sized fruits on cultivar 'Lapins' on Cab 11E, but their size did not differ significantly from those raised on F12-1 or Maxma 14. However, Kappel & Lichou (1994) had better sized 'Burlat' fruits from the cultivar grown on F12-1 than on Edabriz and Maxma 14. Fruit size also increased significantly from the 5th to the 6th leaf in all rootstocks but Gisela 5 (Fig. 3), even with a considerable gain in yield at the 6th leaf. Despite the lower graded fruits produced on the 6th leaf by scions grafted on Gisela 5, their weight was not significantly different from scions on Edabriz. However, fruit size was still good (10.2 g), in the range of 9-11 g, which was defined as appropriate by Lichou et al. (1990) for 'Summit'. Kappel et al. (1996) mention that this weight would not be enough to meet the North American market demands: 11-12g. in our trial, only Cab HE and P. avium, in 2003, promoted a yield good enough for that range. Nevertheless, as seen elsewhere, the vigour of this latter rootstock restrains the intensification of the crop, but Cab 11E combines vigour control with high productivity and some precocity. The relatively poor fruit size on Gisela 5 at the 6th leaf (2003) was probably determined by the high scion bearing in two consecutive years (Fig. 2), and also by the trees not having been pruned until then, which caused an excessive crop load in It has been widely demonstrated that crop load is the main cause of fruit size reduction, and Proebsting (1990) reported that 'Bing' cherry fruit size is negatively correlated to yield if leaf area is relatively constant. Both vegetative and fruit growth are correlated with total leaf area, since leaves are the main source of photoassimilates. With Gisela 5, it was observed that the total leaf area per tree was quite small (Table 1), resulting in as little as 5.6 leaves per fruit at the 6th leaf (Fig. 5). Presumably, fruits were smaller on the 6th leaf because of that low source-sink relationship, 190cm 2 of leaf area per fruit (18.8 cm 2 /g of cherry). This rate is lower than those mentioned by other authors (Whiting 2001; Whiting & Lang 2004) as being susceptible to limit fruit growth.

9 276 New Zealand Journal of Crop and Horticultural Science, 2006, Vol. 34 The number of leaves per fruit observed on cultivar 'Summit' grown on Edabriz, Cab HE, and P. avium was 1.6, 2.3, and 6.4 times higher than on Gisela 5, respectively (Fig. 5). Despite the nonsignificant differences observed in the number of leaves/fruit between Gisela 5 and Edabriz, on this latter rootstock that relation (371 cm 2 leaf area/fruit) did not affect fruit size at the 6th leaf. With Cab HE and P. avium, each fruit could benefit from c. 13 and 36 leaves respectively (c. 533 and 1475cm 2 / fruit), those being high ratios of leaves per fruit; this favours additional vegetative growth as only a small portion of the available photosynthates are directed to fruit growth. The performance of Gisela rootstocks, especially Gisela 5, has been highlighted on several occasions (Franken-Bembenek 1995; Vogel et al. 1997; Wertheim et al. 1998; Franken-Bembenek 2005). It is adapted to several training systems and plant densities, and has been increasingly planted by commercial growers. The results of this work also show that the 'Summit' cultivar grafted onto dwarfing rootstocks Gisela 5 and Edabriz raises precocious, small, and productive trees. From the 5th to the 6th leaf, tree yield increased sharply in every rootstock, and average fruit weight also improved (P < ), except for Gisela 5. The influence of crop yield on fruit size was most apparent at the 6th leaf on the dwarfing rootstocks, particularly on Gisela 5. Consequently, our results emphasise the need to adjust cultural techniques to dwarfing rootstocks, especially Gisela 5 and Edabriz, to keep a good ratio of leaves/fruit and optimise the balance between the quantity of fruits produced and the quality sought after. Cab HE rootstock, though having a lower cumulative yield efficiency than the dwarfing Edabriz and Gisela 5, proved to be very productive, especially at the 6th leaf, and bore better-sized fruits. However, Cab HE requires additional cultural practices to control vigour (i.e., high budding, summer pruning, bending) and de-suckering. This is why the techniques to be adopted in the orchard play a decisive role in the industrial production of superior quality 'Summit' cherry, and must be oriented to perf ectly fit specific stock characteristics and requirements. ACKNOWLEDGMENTS We thank Eng. Mario de Carvalho for helping with the concept of the experimental design. REFERENCES Atkinson CJ, Else MA, Stankiewicz AP, Webster AD Limited availability of photoassimilates: effects on the abscission on sweet cherries. Acta Horticulturae 557: Ayala M Carbon partitioning in sweet cherry (Prunus avium L.) on dwarfing precocious rootstocks during fruit development. Unpublished PhD dissertation, Michigan State University, United States. 254 p. Chariot G, Edin M, Floc'hlay F, Soing P, Boland C Tabel Edabriz: a dwarf rootstock for intensive cherry orchards. Acta Horticulturae 667: De Salvador FR, Piccioni C, Bonofiglio P Performance of new and standard cherry rootstocks in different soils and climatic conditions. Acta Horticulturae 667: Edin M Tabel Edabriz, porte-greffe nanisant du cerisier. Infos, CTIFL55: Edin M Porte-greffe du cerisier. Le point sur Tabel Edabriz. Infos, CTIFL 96: EdinM, Tronel C Cerisier Evolution technique du verger. Nouveaux porte-greffes et variétés. Infos, CTIFL 40: Franken-Bembenek S Vergleichende Darstellung der Versuchsergebnisse mit Giessener Kirschenunterlagen. Erwerbsobstbau 37: Franken-Bembenek S Gisela 5rootstockin Germany. Acta Horticulturae 667: Gonçalves B, Moutinho-Pereira J, Santos A, Silva AP, Bacelar E, Correia C, Rosa E Scionrootstock interaction affects the physiology and fruit quality of sweet cherry. Tree Physiology 26: Gutzwiler J, Lang GA Sweet cherry crop load and vigor management on Gisela rootstocks. Acta Horticulturae 557: Hilsendegen P Preliminary results of a national German sweet cherry rootstock trial. Acta Horticulturae 667: Kappel F, Lane WD Recent sweet cherry introductions from the breeding program at Summerland, British Columbia, Canada. Acta Horticulturae 468: Kappel F, Lichou J 1994 Howering and fruiting of 'Burlat' sweet cherry on size-controlling rootstock HortScience 29(6): Kappel F, Fisher-Heming B, Hogu E Fruit characteristics and sensory attributes of an ideal sweet cherry. HortScience 31(3):

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