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Keywords:

  • anthocyanin;
  • berry mass;
  • canopy management;
  • fruit microclimate;
  • fruitset;
  • leaf removal

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References

Background and Aims

Early defoliation (ED) can reduce vine yield and improve fruit composition in vigorous vineyards. The objective of this study was to test the effectiveness of this technique for the Vitis vinifera (L.) cultivar Tempranillo under the temperate warm and semi-arid climatic conditions of south-eastern Spain.

Methods and Results

Four treatments were applied over three seasons to drip-irrigated vines, planted with rows orientated north–south and shoots vertically positioned. Non-defoliated vines (control) were compared with vines defoliated either just before anthesis (phenological stage H, treatment ED) or at fruitset [phenological stage J, treatment late defoliation (LD)]. In the fourth treatment, only the leaves facing east were removed at phenological stage H (treatment east ED). In the fourth experimental season, all treatments were managed similarly. Defoliation did not reduce fruitset but reduced berry mass, particularly in the ED and the LD treatments. Defoliation, however, had a cumulative negative effect on vine bud fertility. Even in the fourth experimental season, the yield of the ED treatment was 18% lower than that of the control. Both the ED and particularly the LD treatments increased berry total soluble solids (TSS) and phenolic concentration. The effect of leaf removal on berry TSS and phenolic concentration was not significant in the east ED treatment.

Conclusions

Defoliation at fruitset was the most effective treatment for increasing berry phenolics and TSS while maintaining must acidity. Growers should take into account, however, the important yield penalty because of defoliation, particularly in the mid-term.

Significance of the Study

Early defoliation of Tempranillo grapes growing in semi-arid and temperate climates needs to be applied with caution and probably limited to specific seasons while consecutive defoliations should be avoided.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References

Traditionally, defoliation has been used to increase fruit exposure to sunlight and airflow in the fruiting zone to improve berry composition and disease control (Jackson and Lombard 1993). This practice is more often applied in cool climates or to vigorous vines, where fruit microclimate and the environmental conditions are often inadequate to ensure adequate berry ripening. Traditionally, vines are defoliated well after fruitset (i.e. around veraison) when the impact on yield is less (Intrigliolo and Lakso 2009) and potential berry size has been established. Furthermore, later in the season, vines will normally have enough foliage and, therefore, source capacity to withstand a degree of leaf removal. At this time, older leaves with lower photosynthetic activity are removed (Poni et al. 1994).

Several studies have shown that leaf removal earlier in the season (around flowering) can reduce fruitset, fruit growth and even vine yield in the next season (Coombe 1959, Candolfi-Vasconcelos and Koblet 1990, Hunter and Visser 1990a,b). Based on this, Poni et al. (2006) developed a technique commonly referred to as ‘early defoliation’ (ED) to reduce yield and bunch compactness. More recently, Palliotti et al. (2011) showed that when vine photosynthesis capacity is suppressed by spraying the canopy with an antitranspirant, yield can be reduced due to the effect of source limitation during flowering and fruitset.

Previous studies have shown that ED improved fruit composition and reduced bunch compactness in vigorous vineyards in northern Italy (Poni et al. 2006, 2009). More recently, Tardáguila et al. (2010) and Diago et al. (2010) applied ED successfully on cvs Graciano, Carignan and Tempranillo in the relatively cool La Rioja region of Spain. Defoliation of cv. Tempranillo just prior to flowering was more effective for reducing yield than defoliation at fruitset. The same was true for cvs Graciano and Carignan (Tardáguila et al. 2010).

An important advantage of ED is that it can be mechanised (Poni et al. 2008, Tardáguila et al. 2010) and is the focus of current research (Poni and Bernizzoni 2010, Sabbatini and Howell 2010, Filippetti et al. 2011). Early defoliation in warm climates, however, has not been studied. In these climates, ED and subsequent increased fruit exposure may reduce berry colour (Bergqvist et al. (2001).

In Tempranillo vines grown in the semi-arid terroir of south-eastern Spain, Intrigliolo and Castel (2011) showed a strong relationship between yield and final grape composition, irrespective of how yield was manipulated, i.e. water withholding or shoot and bunch thinning. Reducing yield always increased total soluble solids (TSS) and anthocyanins in berries. Bunch thinning is an expensive technique that does not always improve fruit composition (Keller 2010) often because of yield compensatory effects. Consequently, the objective of this study was to evaluate the effect of defoliation applied at different times and at several levels of severity on yield and fruit composition of Tempranillo vines grown in south-eastern Spain.

Materials and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References

Site description

The experiment was carried out during four consecutive seasons (2008–2011) in a Tempranillo vineyard (Vitis vinifera L.) planted in 1991 on 161-49 rootstock at a spacing of 2.45 by 2.45 m (1666 vines/ha). The vineyard was located near Requena (39°29′N, 1°13′W, elevation 750 m), Valencia, Spain. Vines were spur-pruned in winter, leaving 22–23 nodes per vine, and were trained to a vertical trellis on a bilateral cordon system oriented in a north–south direction. Canopy management was manual and included summer pruning carried out before flowering in order to remove all shoots arising from buds from wood more than 1-year old. In addition, shoot tips were trimmed once each season but not until well after fruitset. Drip irrigation was applied with two pressure-compensated emitters of 2.4 L/h located at 60 cm on each side of the vine. All treatments were drip-irrigated to replace half of the estimated crop water needs. Vines were fertilised at a rate of 30-20-60-16 kg/ha of N, P, K, and Mg, respectively. By the end of the season, irrigation application was 130, 174, 60 and 122 mm in 2008, 2009, 2010 and 2011, respectively.

The soil at the site is a Typic Calciorthid, with a clay loam to light clay texture, highly calcareous and of low fertility (0.66% of organic matter and 0.04% of nitrogen). The soil has a deep soil profile (>2 m), and available water capacity is about 200 mm/m with bulk density ranging from 1.43 to 1.55 t/m3. Bud break for Tempranillo in this area usually occurs by mid-April, flowering by early June; veraison is reached by early August, with harvest during September and leaf fall at the beginning of November. Climate can be classified as temperate warm and semi-arid. At the experimental site, the average annual rainfall for the last 12 years was 430 mm of which about 65% falls during the dormant period. The historical growing degree days (base 10°C) from 1 April to 31 October is 1669°C, and the heliothermal index is 2291 corresponding to a temperate warm viticultural climate according to the classification of Huglin and Schneider (1998). Weather conditions during the experiment were measured with an automated meteorological station located in the plot and are reported in Table 1.

Table 1. Growing degree days (base 10°C), rainfall registered from April to October, annual rainfall and average daily maximum air temperature (Tair) during the veraison to harvest period for a Tempranillo vineyard in Requena (Valencia), Spain
 2008200920102011
Growing degree days1464170814651668
Tair (°C)30.732.030.331.4
Rainfall (April–October) (mm)468145331192
Annual rainfall (mm)491454638359

Defoliation treatments

Sixteen vines per treatment were randomly selected within the vineyard and treatments applied were:

  • (i) 
    Control – undefoliated.
  • (ii) 
    ED – Leaf removal was applied just before flowering [phenological stage H, Baggiolini (1952)]. All the leaves of the first six nodes were removed, including leaves from lateral shoots at these node positions.
  • (iii) 
    LD – late defoliation. Leaf removal was applied at fruitset [phenological stage J, Baggiolini (1952)]. All the leaves of the first six nodes were removed, including leaves from the lateral shoots.
  • (iv) 
    EED – east ED. Leaf removal was applied just before flowering (stage H). Only the leaves facing east of the eight first nodes were removed (four leaves), including lateral shoots.

In all treatments, the lateral apices were not removed. In the ED and EED treatments, defoliation was applied on 29 May, 25 May and 2 June of 2008, 2009 and 2010, respectively. In the LD treatment, defoliation was applied on 17, 6 and 14 June of 2008, 2009 and 2010, respectively. In 2011, no defoliation treatments were applied, and vines were assessed to evaluate possible carry over effects of the three consecutive seasons of defoliation on vine performance.

Leaf area determinations

The total area of leaves removed was assessed by weighting the total leaf mass removed from each experimental vine and dividing this by the specific leaf mass [leaf area (cm2)/dry mass (g)]. Existing leaf area at the time of defoliation was quantified by linear equations relating leaf area per shoot and total (main plus laterals) shoot length. These relationships were obtained from samples of 15 shoots of different lengths collected at each time of defoliation in vines outside the experimental plots. In defoliated vines, all existing shoots were measured for leaf area determination. After veraison, when shoot length growth had stopped, the total (main + lateral) shoot length was measured in all experimental vines along with shoots per vine to determine vine leaf area.

Leaf assimilation rates and fruit microclimate determination

Leaf assimilation rate (Pn) was measured in 2008 and 2009. In 2008, only the control and ED treatment were measured, while in 2009, all treatments were measured. Measurement of Pn was conducted under ambient light, temperature, relative humidity, and air CO2 conditions between 10 and 11 am solar time using a portable IRGA system (Model ADC LC Pro+, The Analytical Development Co. Ltd, Hoddesdon, England) on 12 mature, well-exposed leaves per treatment. In all treatments, leaves of similar age were randomly selected among the experimental vines. Leaves were most often located in the 7–9 bud position within a shoot.

Microclimate conditions in the fruit zone were measured during the second experimental season (2009). Berry temperature was measured in six berries per treatment by inserting the probe of a dual hypodermic thermocouple (Omega Engineering, Inc., Stamford, CT, USA) into the centre of the berry. This insertion did not affect berry development as indicated by measurement of berry diameter with a digital calliper. Determination of berry temperature started after fruitset and continued until the end of the ripening period. Thermocouples readings were registered continuously using a datalogger and multiplexer (CR1000 + AM25T, Campbell Scientific, Logan, UT, USA) programmed to report 30-min average values.

Light intensity in the fruit zone was assessed by measuring the photosynthetically active radiation (PAR) using 50-cm length bar sensors (Skye Instruments Ltd, Llandrindod Wells, Wales) positioned within the fruiting zone. Because of availability of the sensors, only a single bar per treatment was used. Above canopy, PAR was measured by means of a single PAR quantum sensor (Skye Instruments Ltd). Readings of PAR were recorded from 25 June to 30 August by a CR1000 datalogger (Campbell Scientific) programmed to report average 30-min values. Data obtained during entire days were averaged in order to calculate daily average values.

Flowering, fruitset and yield determination

In all experimental vines, four inflorescences were selected just before anthesis and photographed against a dark background with a digital camera held perpendicular to the inflorescence. A regression between actual flower number (obtained by destructive counting on 30 inflorescences in 2008 and 14 per year in seasons 2009, 2010 and 2011 – inflorescences taken from guard vines) and the number of flowers counted on photo prints was then established. The resulting linear relationship (no flowers = 2.06 x no flowers photo; r2 = 0.96*** n = 72) was then used to estimate the actual flower number per inflorescence. This regression equation was used in all four seasons as there was no significant (P < 0.05) difference observed among seasons. The same selected inflorescences tagged for flower number determination were harvested 1–2 days before the commercial vintage and the number of berries per bunch counted to obtain the fruitset rate and weighed to obtain the bunch and berry fresh mass. At harvest, the remaining bunches per vine were counted and weighed separately to obtain the total yield per vine. Harvest was carried out on 29, 1, 20 and 23 September of 2008, 2009, 2010 and 2011, respectively.

Fruit composition

Must composition was measured in four samples per treatment comprising about 300 berries. Half of the sample was crushed with a Thermomix blender and hand-pressed through a metal screen filter. Juice was then centrifuged during 10 min at 17608 × g. TSS (°Brix) was determined by refractometry. Juice pH and titratable acidity (TA) were determined by an automatic titrator (Metrohm, Herisau, Switzerland). Juice was titrated with a 0.1 N solution of NaOH to an end point of pH 8.2, and results were expressed as g/L of tartaric acid. Malic and tartaric acids were determined using a Systea Easychem Plus automatic sequential analyzer (Easychem, Oak Brook, IL, USA). Tartaric acid was measured according to the spectrophotometric method of Rebelein (Blouin 1973), and malic acid was measured using the enzymatic method described by Chretien and Sudraud (1993). Duplicate samples were measured for all must components.

Total anthocyanins (expressed in malvidin equivalents), total phenols (in absorbance units) and tannins (in catechin equivalents) were determined in triplicate by ultraviolet/visible spectrophotometry in samples of 150 berries homogenised (Ultraturrax T25) to a grape paste (Iland et al. 2004). Two samplings were performed each season on 9 and 29 September 2008, 26 August and 1 September 2009, and 7 and 20 September 2010. The second sample collection coincided with commercial harvest.

Statistical analysis

Analysis of variance was undertaken with the mixed procedure of the SAS statistical package (version 8.2; SAS Institute, Inc., Cary, NC, USA). Differences among treatments were assessed by Duncan's Least Significant Difference test. Data across seasons were also analysed including the year and treatment by year factors. In this case, differences between means were analysed only when the interaction treatment by year effect was not statistically significant at P < 0.05 (i.e. the effect of the treatment was not different in each season). For berry components, differences between treatment means were assessed within each sampling date with a Duncan's least significant difference test and also by comparing with a Dunnett's t-test data from the control vines for the late sampling with those from the defoliated vines for the first early sampling.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References

Climatic conditions

Growing degree-days from April to October in all years were above 1464°C and in 2009 reached 1708°C (Table 1). During the berry-ripening period (i.e. August and beginning of September), average daily maximum air temperature varied from 30.3 to 32°C, registered in 2010 and 2009, respectively. Rainfall was relatively low in 2009 with only 145 mm registered for the entire April to October period (Table 1). During 2008 and 2010, a higher annual precipitation rate was recorded reaching a maximum value of 638 mm (Table 1).

Leaf area removed and vine vegetative growth

In all experimental seasons, the highest amount of leaf area removed with defoliation was registered in the LD treatment where, pooling data across seasons, an average of 3.7 m2 of leaf area was removed, which represented about 69% of the total leaf area (Table 2). When values were expressed in relative terms, however, the highest proportion of leaf area was removed in the ED treatment, with up to 80% of the total leaf area present at phenological stage H removed (Table 2).

Table 2. Leaf area removed in a Tempranillo vineyard under three defoliation regimes
ParameterTreatment200820092010AverageYearTreat*year
  1. Within each column, different letters indicate a significant difference among treatments after Duncan test at P < 0.05. Data are average values (n = 16) for the defoliation treatments applied either before flowering (ED), at fruitset (LD) or at flowering, removing leaves facing the east side of the canopy (EED). Leaf area removed is reported in absolute terms and also relative to the total vine leaf area at the time of defoliation. For the analysis of the data across years, the statistical significance of the effect of year and treatment by year interaction are also indicated. ED, early defoliation; EED, east ED; LD, late defoliation.

Total leaf area removed (m2/vine)ED1.5b2.1b1.9b1.8b<0.00010.238
LD2.9a3.3a4.8a3.7a
EED1.3b1.5c1.3c1.4c
Leaf area removed as a proportion of the total (%)ED79a93a69a80a<0.00010.195
LD58b84a66a69b
EED55b60b47b54b

Average vine shoot length at phenological stage H was similar in all treatments and seasons (Table 3). Later in the season, defoliation increased shoot length by 25% compared with that of the control vines but only in the first experimental season and only in the ED and LD treatments. This increase was mainly a consequence of a shoot lateral regrowth (Table 3). In contrast, in 2009 and 2010, similar total shoot length values were registered in all treatments (Table 3).

Table 3. Shoot length at several phenological stages in a Tempranillo vineyard under three defoliation regimes
ParameterTreatment200820092010AverageYearTreat*year
  1. Within each column, different letters indicate a significant difference among treatments after Duncan test at P < 0.05. Data are average values (n = 16) for the control, and the defoliation treatments applied either before flowering (ED), at fruitset (LD) or at flowering, removing leaves facing the east side of the canopy (EED). For the analysis of the data across years, the statistical significance of the effect of year and treatment by year interaction is also indicated. ED, early defoliation; EED, east ED; LD, late defoliation.

Main shoot length at phenological stage H (cm)Control71a73a53a63a<0.00010.299
ED66a67a53a60a
LD68a68a53a61a
EED70a71a53a62a
Total (main + laterals) shoot length after veraison (cm)Control177a181a155a171<0.00010.0432
ED222b162a140a175
LD222b179a145a182
EED210ab172a150a177
Lateral shoot length after veraison (cm)Control45b46a18a36<0.00010.0345
ED73a39a13b42
LD77a52a16a48
EED89a48a15ab51

Leaf assimilation rates and fruit microclimate

Leaf assimilation rates for the different treatments are reported in Figure 1. In 2008, compared with that of control vines, Pn for the ED vines increased once defoliation was applied. In 2009, when a more comprehensive analysis of leaf assimilation rates was conducted, the ED treatment maintained a Pn value higher than that of the control until the beginning of July. Afterwards, Pn of the ED treatment decreased to a value close to that of the control. In contrast, Pn for the EED treatment was in all determinations, except for that in mid-August, close to that of control, indicating that in this treatment, leaf assimilation rate was not affected by defoliation. In the LD treatment, immediately after defoliation was carried out, Pn was close to that of the control, but it increased to a value about 30% higher than that of the control 20 days after the application of the treatment, and the value remained 20–40% higher than that of the control until September (Figure 1). The Pn value in the control vines increased during the first part of the season, reaching a leaf assimilation rate of 12 μmol/(m2·s) recorded in mid-July. Afterwards, Pn of the control vines had a decreased to a value around 6.5 μmol/(m2·s).

figure

Figure 1. Seasonal variation of leaf assimilation rates (Pn) in a Tempranillo vineyard under different leaf defoliation regimes in (a) 2008 and (b) 2009. Data are average values for the control, undefoliated vines (●) and the defoliation applied before flowering [early defoliation (ED)] (○), at fruitset [late defoliation (LD)] (▼) or at flowering, but removing leaves facing the east side of the canopy (east ED) (▽). The dotted and solid vertical lines indicate the time when defoliation was applied in the ED and LD treatments, respectively. In 2008, Pn was determined only in the control and ED treatments. Error bars are the standard error values.

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Light exposure in the fruit zone was the maximum in the LD treatments, with about half of incident PAR reaching the fruit (Figure 2). The ED and EED treatments had similar fruit exposure, with about one third of the available light reaching the fruit zone. In the control treatment, an average of only 4.7% of the ambient PAR light penetrated to the fruiting zone.

figure

Figure 2. Seasonal variation (a) of the photosynthetically active radiation (PAR) above the canopy (—) and reaching the fruit zone (○,●,▽,▼) and (b) of the daytime and night-time berry temperature in a Tempranillo vineyard under three defoliation regimes. Data are average values (n = 6) for the control (no defoliation) (●), for the defoliation applied before flowering [early defoliation (ED)] (○), at fruitset (late defoliation) (▼) or at flowering, but removing leaves facing the east side of the canopy (east ED) (▽). Daytime (●,○,▼,▽) and night-time (■,□,◆,◇) temperatures are average values for the periods 07:00–20:00 and 22:00–06:00 solar time, respectively. PAR radiation values are daily averages. In the berry temperature graph, the error bars are the standard deviations.

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Berries from defoliated vines had 1–2°C higher daytime and 0.5–1°C lower night-time temperature than that of control berries (Figure 2). Berry temperature difference among the different defoliation treatments was not as clear. Shortly after fruitset, the ED had a berry temperature slightly higher than that of the LD and EED treatments. The berry growing degree-days (base 10°C) calculated from berry temperature data showed that Control and EED treatments were not statistically different at 967 and 981°C*day, respectively, while the ED and LD treatments values (998 and 999°C*day, respectively) were significantly (P < 0.05) but not substantially higher than that for the Control and EED treatments.

Yield components

The average number of shoots per vine retained after summer pruning was similar in all treatments and ranged from 22 to 23 across seasons (results not shown). In the first experimental season, a similar number of bunches per shoot was recorded in all treatments (Table 4). Only in 2011, after three consecutive seasons of defoliation application, a significant decrease in the number of bunches per shoot could be recorded in the ED treatment compared with that of the control. Pooling data from 2009 to 2011 (the years when the defoliation carried out in the previous seasons could have affected bud fertility), the number of bunches per shoot of the ED treatment was 28% lower than that in the control vines (Table 4). In 2008 the number of florets per inflorescence was similar in all treatments (Table 4). This was not surprising since the defoliation treatments started in 2008. In 2009 and 2010, however, defoliation carried out at phenological stage H (i.e. the ED treatment) decreased by 22–25% the number of florets per inflorescence, whereas in 2011, the number of florets per inflorescence of the ED treatment returned to a value similar to that of the control. The LD and EED treatments did not significantly affect the number of inflorescences per shoot or the number of florets per inflorescence compared with the control treatment in any of the experimental seasons (Table 4).

Table 4. Effect of early defoliation on bud fertility and yield components of Tempranillo grapevines under three defoliation regimes
ParameterTreatment2008200920102011AverageYearT*year
  1. Within each column different letters indicate a significant difference among treatments after Duncan test at P < 0.05. Data are average values (n = 16) for the control, and the defoliation treatment applied either before flowering (ED), at fruitset (LD) or at flowering, removing leaves facing the east side of the canopy (EED). For the analysis of the data across years, the statistical significance of the effect of year and treatment by year interaction is also indicated. For the variables bud fertility and flowers/inflorescence average data correspond to the 2009–2011 period; for the other variables, the averages are for the 2008–2010 period. Fruitset, berries/bunch and bunch mass were not obtained in 2011 when defoliation was not applied in any treatment. —, no data collected; ED, early defoliation; EED, east ED; LD, late defoliation.

Bud fertility (inflorescences per shoot)Control1.31a0.76a0.97a1.32a1.01a<0.00010.8955
ED1.20a0.54a0.68a0.97b0.73b
LD1.20a0.65a0.76a1.18a0.87ab
EED1.26a0.67a0.77a1.20a0.88ab
Flowers per infloresenceControl379a304a430a468a401a<0.00010.0885
ED353a229b353b478a353a
LD362a310a396ab470a393a
EED400a281ab456a456a398a
Fruitset (%)Control42.5a43.8a38.2a41.4a<0.0010.466
ED42.0a43.5a33.1a39.6a
LD42.5a41.0a36.6a40.0a
EED42.3a48.2a38.5a42.9a
Berries per bunchControl155a149a160a155a0.0180.084
ED140a130a104b124b
LD144a138a124ab135b
EED161a149a155a156a
Berry mass (g)Control1.95a2.06a1.78a2.0a<0.0010.508
ED1.75b1.89b1.62b1.82b
LD1.73b1.76b1.58b1.69c
EED1.90ab1.91b1.84ab1.89ab
Bunch mass (g)Control282a275a278a277a281a0.0010.054
ED230b219b153b304a234b
LD255b248b172b308a237b
EED317a299a256a281a305a

Fruitset did not vary among all treatments in any of the experimental seasons (Table 4). In 2010, however, there were still differences in the number of berries per bunch among treatments because the ED treatment significantly decreased the number of berries per bunch compared with that of the control and EED treatments (Table 4). When pooling data across seasons, both the ED and LD reduced by 20 and 13%, respectively, the number of berries per bunch, while the EED did not impair this variable when compared with that of the control, the ED and the LD treatments.

Berry mass was the yield component variable more consistently affected by defoliation. Pooling data across seasons, the ED and LD treatments decreased berry mass by 9 and 16%, respectively, compared with that of the control vines. There was also a significant difference between ED and LD, with the LD treatment resulting in a greater reduction in berry mass. In contrast, compared with the control treatment, the effect of the EED defoliation regime on berry mass was statistically significant only in 2009 (Table 4).

In all seasons in which defoliation was applied, the ED and LD treatments reduced bunch mass (Table 4). Considering average data for 2008, 2009 and 2010, bunch mass was 25% lower in the ED and LD treatments compared with that of the control, and differences between the ED and EED treatments were also noticeable and statistically significant (Table 4). In 2011, when defoliation was not applied, similar bunch mass was recorded in all treatments.

Vine vegetative growth and yield

Total vine leaf area was significantly affected by defoliation only in the ED and LD treatments (Table 5). The reduction observed varied among seasons with the greatest reduction (−45%) observed in the LD treatment in 2008 and the least pronounced (−14%) in the ED treatment in 2010. It should be noted that defoliation applied in the EED treatment did not significantly affect total leaf area (Table 5).

Table 5. Leaf area, yield and leaf area to yield ratio of Tempranillo grapevines under three defoliation regimes
ParameterTreatment2008200920102011AverageYearT*Year
  1. Within each column, different letters indicate a significant difference among treatments after Duncan test at P < 0.05. Data are average values (n = 16) for the control, and the defoliation treatment applied either before flowering (ED), at fruitset (LD) or at flowering removing, leaves facing the east side of the canopy (EED). For the analysis of the data across years, the statistical significance of the effect of year and treatment by year interaction is also indicated. Leaf area was not determined in 2011 when leaf pulling was not applied in any treatment. —, no data collected; ED, early defoliation; EED, east ED; LD, late defoliation.

Leaf area (m2/vine)Control7.9a7.7a13.0a9.5<0.00010.034
ED6.1b5.0b11.2b7.4
LD4.4b5.6a12.9a7.6
EED6.7ab6.3a11.6ab8.2
Yield (t/ha)Control11.1a9.2a11.9a13.2a10.7<0.00010.049
ED8.6b4.6b5.1d10.9b6.1
LD8.2b5.0b6.4c12.8a6.5
EED9.3ab6.7b8.6b11.6ab8.6
Leaf area/yield (m2/kg)Control1.14a1.33b1.74b1.41<0.00010.023
ED1.14a1.74a3.51a2.13
LD0.86b1.78a3.23a1.96
EED1.16a1.50ab1.87b1.51

The effect of defoliation on yield also varied among seasons and tended to become more pronounced over the years (Table 5). For instance, in 2008, yield in the ED treatment was reduced with respect to that of the control vines by 23%, while in 2009, it decreased by 50% and in 2010, the yield reduction was as high as 54%. In 2011, when defoliation was not applied and the ED vines were managed similarly to the Control vines, there was a carry-over effect, and an 18% reduction in yield was recorded (Table 5). In the first two experimental seasons in the LD treatment, the yield reduction compared with that of the control treatment was similar to that reported for the ED. In 2010, however, the LD treatment reduced yield less than the ED treatment, with a statistical significant difference between these two treatments. In 2011, the LD and the control treatments yielded similarly. In the EED treatment, yield was reduced by 28% compared with that of the control vines in 2009 and 2010.

Grape composition

Grape composition for each single season (2008, 2009 and 2010) is presented in Figures 3 and 4. It should be highlighted, however, that the defoliation treatment by season interactive factor was not statistically significant at P < 0.05 for any of the grape composition parameters analysed. This suggests that in general, the trends observed were consistent among seasons. Data are separated in the two samplings obtained before harvest (early sampling) and at harvest (late sampling). Differences among treatments are reported within each sampling date and also between values of the defoliation treatments in the early sampling and the control treatment for the late sampling.

figure

Figure 3. Concentration of sugar [total soluble solids (TSS)], and tartaric and malic acids, pH and titratable acidity of berries on two sampling dates at the end of the ripening period in a Tempranillo vineyard under three defoliation regimes. Averages are obtained from four replicates per treatment for the control (no defoliation) and for the defoliation applied before flowering [early defoliation (ED)], at fruitset [late defoliation (LD)] or at flowering, but removing leaves facing the east side of the canopy (east ED). Within each sampling date, different letters indicate statistically significant differences at P < 0.05 after Duncan test. *Indicates significant differences at P < 0.05 among the early samples of the defoliation treatments and the late sample of the control treatment. The horizontal dotted lines mark the value of the LD treatment for the early sampling.

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figure

Figure 4. Concentration of total phenolic, total anthocyanins and tannins at two sampling dates at the end of the ripening period in a Tempranillo vineyard under three defoliation regimes. Data are obtained in four replicates per treatment for the control (no defoliation) and for the defoliation applied before flowering [early defoliation (ED)], at fruitset [late defoliation (LD)] or at flowering, but removing leaves facing the east side of the canopy (east ED). Within each sampling date different letters indicate statistically significant differences at P < 0.05 after the Duncan test. * indicates a significant difference at P < 0.05 among the early samples of the defoliation treatments and the late sample of the control treatment. The horizontal dotted lines mark the value of the LD treatment for the early sampling.

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In all three seasons and for both sampling dates, grape TSS was significantly increased by the LD treatment compared with that of the control vines (Figure 3). In the first two seasons, this TSS increment was still noticeable when compared with that of control samples collected some 15 days later (Figure 3). When compared with control values, the ED treatment significantly increased TSS only in the early sample of the last experimental season. The EED treatment had, in all seasons, a similar TSS value to that of the control and the LD berries. On each sampling date, defoliation tended to decrease TA and to increase must pH, respectively, compared with that of the control vines. Differences in must acidity with respect to the control values were more noticeable in the LD treatment and in the last two experimental seasons. However, on comparing values of the defoliation vines for the early sampling with those of the late sampling, it was observed that ED resulted in an increase in must acidity concentration and a decrease in must pH (Figure 3).

Defoliation had a variable effect on the concentration of the organic acids. Thus, on each sampling date, while tartaric acid increased in the defoliation treatments LD and EED, malic acid decreased, and the effect was statistically significant in the LD treatment. In the last two experimental seasons, however, malic acid concentration of the defoliation treatments at the early sampling was similar to that of the control late sampling (Figure 3).

Defoliation also clearly affected the grape phenolic composition (Figure 4). In all seasons, the ED and particularly the LD treatments increased the concentration of total phenolics and anthocyanins in berries. For the LD treatment, this effect was still statistically significant even when comparing samples with a 2-week difference. In contrast, the EED treatment did not increase the concentration of grape phenolics when compared with that of the control samples. Despite the fact that there was a general trend for the LD treatment to have a concentration of total phenolics and anthocyanins higher than that of the ED treatment, the difference between these two defoliation treatments was in most cases not statistically significant at P < 0.05. Grape tannins concentration was also increased in the LD treatment compared with that of the control treatment in the first two seasons (Figure 4). Pooling data for all three seasons, for instance, the concentration of total phenolics, anthocyanins and tannins was 13, 18 and 48 units higher in the early sampling of the ED treatment compared with that of the late sampling of the control treatment.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References

ED effects on grape composition

To the best of our knowledge, this study is the first to report on the effect of ED in a relatively warm and dry climate. Since the original study by Poni et al. (2006), ED has been the subject of several investigations in relatively cool and humid viticultural sites (Diago et al. 2010, Poni and Bernizzoni 2010, Sabbatini and Howell 2010). Overall, the results agree with previous studies (Poni et al. 2006, Diago et al. 2010, Poni and Bernizzoni 2010), which showed that ED when severe, i.e. by removing all main leaves and lateral leaves of the first six nodes, increased TSS (Figure 3) and phenolic concentration (Figure 4). Other studies conducted in high light and high temperature areas have reported that berry colour could be reduced by defoliation (Bergqvist et al. 2001, Spayd et al. 2002). Those studies recommended caution as to the timing for applying leaf defoliation under warm and arid environments. Our results, similar to those of Palliotti et al. (2011), suggest that leaf removal can be effective early in the season, when air temperature is still mild and when berries are at an early stage of growth and development. Under these circumstances, it is likely that berries and vines can withstand sudden high exposure to sunlight by either promoting the growth of skin tissues (Poni et al. 2008) or a lateral regrowth to compensate for the defoliation (Poni et al. 2006).

There are three possible explanations for the positive responses reported here. First, berry mass was lower in the defoliation treatments. Smaller berries have a higher surface area to volume ratio, increasing the concentration of phenolic substances mainly present in skin tissues (Roby et al. 2004). In fact, the largest effect of leaf removal on berry TSS and phenolic concentration was observed in the LD treatment (Figures 3, 4), the treatment with a greatest effect on berry mass (Table 4). Second, crop level was also lower in the defoliated vines, and previous studies (Intrigliolo and Castel 2011) suggest that yield per se can affect TSS and berry colour. In addition, at least in the final two experimental seasons, vine crop load was lower (higher leaf area to yield ratio) in the defoliation treatments (Table 5). Third, it is possible that fruit microclimate was improved by defoliation. The fact that defoliation was applied early in the season and lateral apices were not removed might have led to more favourable light conditions, which avoided excessive sun exposure while only slightly increasing berry temperature. In support of this contention, berry temperature in defoliated vines did not exceed 35°C (Figure 2), a temperature above which has a deleterious effect on colour (Kliewer 1977, Mori et al. 2007). In addition, berries from the defoliation treatments had higher daily thermal variation compared with that of control vines, with night-time berry temperature being higher in the control vines (Figure 2). This was most likely due to the higher amount of foliage that control vines had in the fruit zone, which presumably increased the resistance to heat exchange between berries and the surrounding environment. Lower night-time berry temperature can favour berry coloration (Kliewer and Torres 1972, Tomana et al. 1979).

Although defoliation increased TSS and phenolics in berries, it should be noted that this was not the case on a whole vine basis (Table 5) as the reduction in grapevine yield in all treatments was larger than the increase in TSS and phenolic concentration in berries (Figures 3, 4). Thus, overall vine performance was not stimulated by the defoliation treatments. The positive response that severe defoliation had on leaf assimilation rates diminished during the last part of the season (Figure 1) coinciding with berry ripening, including sugar accumulation. In addition, contrary to a previous study on Sangiovese grapevines (Palliotti et al. 2011), Tempranillo grapevines grown in an arid climate did not exhibit regrowth potential (Table 3) possibly because of soil water limitation as only half of the potential evapotranspiration was replaced with irrigation. Indeed, the deficit irrigation applied limited plant functioning towards the end of the season as reflected in the leaf photosynthetic responses (Figure 1).

The only important negative effect that defoliation had on grape composition was the decrease in must TA and increase in must pH (Figure 3). This is particularly problematic for Tempranillo grapes grown in southern Spain, where must pH can often be too high for normal vinification practices. Despite the fact that in many other ED trials, must acidity was not modified by defoliation (Intrieri et al. 2008, Tardáguila et al. 2008, Poni and Bernizzoni 2010), the results reported here are not surprising. This is mainly due to the fact that leaf defoliation decreased berry malic acid concentration (Figure 3) probably because of higher berry temperature (Ford 2012), with berry GDD accumulation in the defoliated vines being higher than in control vines. In addition, berries from the defoliation treatment had higher TSS. Similarly, Diago et al. (2012) found defoliation-improved fruit ripeness. Interestingly, even though fruit was sampled earlier, berries from the LD vines had higher TSS and phenolic concentration than berries from the control vines, which were sampled 7–20 days later (Figures 3, 4). In addition, must pH from the early sample of the LD treatment was lower than that from control grapes picked in the later sampling (Figure 3). This suggests that when defoliation is applied in commercial Tempranillo vineyards under temperate warm and dry conditions harvest could be advanced to counteract the possible negative effect that defoliation might have on berry acidity. Further studies need to be conducted to understand how wine sensory properties are affected by defoliation as wine quality is not purely a function of TSS and berry acidity. For instance, several skin maturity components that were not analysed in the present research are known to be affected by defoliation (Diago et al. 2010, 2012) and by the degree of grape ripening (Keller 2010).

Timing and intensity of leaf removal

We initially hypothesised that removing leaves only from the east side could be a better practice. Unfortunately, these treatment vines were defoliated only at phenological stage H, which turned out to be the less effective of the two timings tested here. Indeed, when an average 54% of the total leaf area was removed at stage H, as in treatment EED, vine performance and fruit composition was not affected. It appears that defoliation needs to be severe to significantly affect vine performance. Tardáguila et al. (2008) found that removing the leaves in Grenache vines only from the first five nodes without eliminating lateral leaves did not affect yield. Vines can compensate in response to leaf removal by increasing the area of remaining leaves (Poni et al. 2006) and by increasing the rate of leaf CO2 assimilation (Poni et al. 2008). Both of these short-term responses were detected in this study (Table 3 and Figure 1). However, in the mid-term (second season of leaf removal application), only leaf assimilation was increased by severe defoliation treatments. Only in the first season did vines respond to defoliation through increasing leaf area. In subsequent seasons, shoot growth was not increased by defoliation, perhaps suggesting a reduction of vine regrowth capacity over time.

The more severe defoliation treatments did not affect fruitset even over three seasons of consecutive leaf removal (Table 4). Although the vine source reduction because of leaf removal affected berry growth, it was probably not severe enough to cause berries to be shed. Similarly, Diago et al. (2010) showed that severe defoliation of Tempranillo grapes in La Rioja (northern Spain) carried out by removing the first eight basal leaves at fruitset did not reduce the number of berries per bunch. More recently, Gatti et al. (2012) showed that fruitset was affected by defoliation after only two consecutive seasons of leaf removal. Research conducted on other grape cultivars, however, has shown that fruitset is often clearly reduced by defoliation while berry growth is unaffected (Poni et al. 2008, Sabbatini and Howell 2010). Intrigliolo and Lakso (2009) showed that berry abscission can be related to the berry growth rate in two species of the Vitis genus, highlighting important differences among plant materials. It is possible that different cultivars or different environmental conditions might determine different berry growth and berry drop patterns in response to a carbohydrate source limitation. It may be that Tempranillo grapes need a drastic decrease in berry growth in order to promote berry abscission. In any case, more research is needed to better understand and predict responses to leaf removal around flowering.

The fact that defoliation affected berry mass but not fruitset has implications not only for yield control but also for fruit composition because a reduction in individual berry mass might have a greater effect on final grape composition rather than a reduction in the number of berries per bunch. Although berry size per se is not the only determinant of must composition (Matthews and Nuzzo 2007), smaller berries could facilitate greater extraction during fermentation of phenolic substances localised in the berry skins, leading to more concentrated wines. More research evaluating the effects of defoliation on the skin tissues growth is needed. Recent studies by Poni et al. (2009) and Palliotti et al. (2011) have shown that relative skin mass in defoliated berries was higher than that in the control berries, even when comparing berries of similar size (Poni et al. 2009).

In contrast with previous findings obtained in La Rioja with Tempranillo, Grenache and Carignan vines (Diago et al. 2010, Tardáguila et al. 2010), showing preflowering defoliation to be more effective than post-flowering leaf removal for regulating yield, our results show that defoliation at fruitset (phenological stage J) had a greater effect on yield via berry mass. In addition, berry TSS was clearly increased by defoliation, particularly when applied at phenological stage J. This may be due to higher exposure to light in treatment LD compared with that in ED.

Mid-term effects of defoliation on vine performance

Particularly in the treatment ED, defoliation decreased both inflorescences per shoot and flowers per inflorescence. It is well known that a carbohydrate source limitation occurring around flowering can reduce bud fertility in the next season (May 2000). It is not clear, however, why the ED treatment decreased bud fertility more than the LD treatment (Table 4). Candolfi-Vasconcelos and Koblet (1990) in cultivar Pinot Noir showed that the period from flowering to 2 weeks after was the most critical for bud fruitfulness responses to defoliation applied the previous season. This period of time covers both the ED and LD treatments. Thus, for Tempranillo, bud fertility may be more sensitive to the period just before flowering than the period after flowering (phenological stage J). The greater effect that ED had on bud fertility might also be due to a greater limitation in carbohydrate supply. More leaves were removed with the treatment also lasting longer (earlier defoliation). Similar to the present results, Candolfi-Vasconcelos and Koblet (1990) showed, after two seasons of leaf removal, that even in a third season in the absence of leaf removal, vines still exhibited reduced bud fertility and berry mass. Vines needed two seasons without defoliation to recover. Other previous studies have not shown such marked reductions in bud fertility over time because of the ED (Poni et al. 2008, Poni and Bernizzoni 2010, Palliotti et al. 2011). Mainly, this has been attributed to any negative effects because of the source being counteracted by higher bud exposure to light.

Bud fertility varied substantially between seasons (Table 4). A recent review by Clingeleffer (2010) on crop management concluded that seasonal differences in bud fertility were a major determinant of vineyard productivity. The marked season-to-season differences in bud fruitfulness observed here had as much of an effect on yield as defoliation.

Overall, the long-term results obtained suggest that preflowering defoliation should not be carried out in deficit-irrigated Tempranillo vines under relatively warm conditions in contrast with what has been previously suggested for this cultivar in a cooler climate (Diago et al. 2010). These contrasting results clearly point out the importance of conducting local research before extrapolating results across environmental conditions.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References

Overall results indicate that in a temperate warm and arid environment under deficit irrigation, defoliation at fruitset by removing all leaves from the first six nodes is the most effective treatment to reduce bunch and berry mass, and to increase berry phenolics and TSS. Growers should take into account, however, the yield penalty because of defoliation, particularly in the mid-term. ED in Tempranillo growing in semi-arid and warm climates needs to be applied with caution and should probably be limited to specific seasons. Consecutive ED should be avoided.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References

This research was supported by funds from the Spanish Ministry of Economy and Competitiveness with European regional development fund co-financing Projects RTA2008-00037-C04-01 and AGL2011-30408-C04-04, and a grant agreement with CajaMar and Fundación Lucio Gil de Fagoaga. Dr Intrigliolo acknowledges the financial support received from the Spanish Ministry of Economy and Competitiveness program ‘Ramón y Cajal’. Thanks are also due to Mr Felipe Sanz, Mr Javier Castel and Ms Angela Martinez for help in field determinations and analytical data.

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  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. References
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