Abstract
Early leaf removal is an innovative cultural practice for yield management in grapevines. The effects of timing (prebloom and fruit set) and method (manual or mechanical) of defoliation on yield components, Botrytis incidence, and wine sensory attributes of Vitis vinifera L. cv. Tempranillo VSP-trained grapevines were examined over two consecutive seasons, 2007 and 2008. Yield per vine was severely reduced (15 to 50%) by manual and mechanical leaf removal at prebloom in the two years and smaller clusters with fewer berries were obtained. At fruit set, only mechanical defoliation was effective at modifying cluster weight, berry number, and yield per vine. Botrytis rot incidence was significantly reduced by early leaf removal in 2008, when an overall higher infection rate was linked to unusually high rainfall. Total leaf area was generally unaffected by early leaf removal. Prebloom defoliation exhibited full recovery of leaf:fruit ratios compared with nondefoliated vines, regardless of defoliation method. Descriptive analysis of the aroma attributes of the wines revealed lowered intensity of fruity, floral, and licorice in the defoliated samples in 2007. Intensity scores for these descriptors were positively correlated to yield and negatively correlated to total leaf area:yield ratio. When Botrytis rot was widespread, the extent of infection was negatively correlated to certain fruity and floral aromas and positively correlated to dried fruit character. Several factors linked to early defoliation, such as yield, Botrytis, and cluster exposure significantly contributed to final wine aroma properties. Principal component analysis illustrated the separation of wines from defoliated and nondefoliated treatments by aroma profile.
Yield management is a key technique in modern viticulture and is widely recognized as an important factor in the composition of resultant wines. In many European countries, grape yields are regulated by law, reportedly for quality control. Winter pruning and cluster thinning are widely applied in viticulture for yield control. Pruning effects on wine sensory properties have been studied, and whereas one study reported no consistent effects of yield on wine quality scores (Freeman et al. 1980), another reported wine aroma and flavor differences due to yield manipulation by winter pruning over two consecutive seasons in Cabernet Sauvignon (Chapman et al. 2004). In this latter study, wines made from vines pruned to low bud numbers (low yield) were described as less fruity and more vegetative, bitter, and astringent than wines made from vines pruned to high bud numbers (high yield). Grape and wine quality have been improved by cluster thinning (Reynolds et al. 2007). However, other researchers have shown no impact of cluster thinning on grape and wine composition (Chapman et al. 2004, Keller et al. 2005). Furthermore, manual cluster thinning is labor intensive and expensive.
Recently, two alternative techniques were tested for yield management: mechanical cluster thinning (Petrie and Clingeleffer 2006, Tardaguila et al. 2008b) and early leaf removal (Poni et al. 2006, Intrieri et al. 2008). Early leaf removal is an innovative viticultural practice for regulating yield components and improving grape quality. Early defoliation is conducted around bloom, unlike classical leaf removal, which is typically conducted between fruit set and veraison. Since basal leaves are the main source of assimilates at flowering, their removal reduces berry set, leading to smaller and looser clusters, with fewer berries of better and more homogeneous quality (Poni et al. 2006, 2009, Intrieri et al. 2008). In these studies, grape composition also improved in defoliated vines as higher soluble solids and anthocyanin concentrations increased. Most of the research was conducted on manual early defoliation (Poni et al. 2006, 2009), but there is a general consensus on the need to assess the feasibility of a mechanical approach. The effects of mechanical early leaf plucking on composition of Sangiovese grapes have been investigated (Intrieri et al. 2008).
Leaf removal improves light exposure and air circulation around clusters (Bledsoe et al. 1988), while cluster thinning, used most frequently for yield control, does not affect canopy microclimate. Early leaf removal not only affects yield per vine (Poni et al. 2006, Intrieri et al. 2008) but also increases fruit exposure and canopy porosity (Tardaguila et al. 2010). A study on the effect of cluster light exposure on sensory properties of Shiraz wine showed that shading fruit resulted in reduced norisoprenoids in the wine and may alter other compounds that influence wine flavor (Ristic et al. 2007). Another study identified increases in wine constituents, color density, cultivar character intensity, and overall wine quality in wines from defoliated vines compared to wines from nondefoliated vines (Hunter et al. 1995).
Apart from yield and fruit exposure, the timing of basal leaf removal influences grape and wine composition (Tardaguila et al. 2008a). Grenache wines made from vines defoliated at fruit set were rated higher in aroma complexity, mouthfeel, tannin quality, and persistence than wines made from vines defoliated at veraison. For the wine industry, it would be very useful to assess the impact of early leaf removal on wine sensory attributes. The aim of this study was to evaluate the effects of timing (prebloom and fruit set) and method (manual and mechanical) of early defoliation on aroma properties of the resulting Vitis vinifera L. cv. Tempranillo wines.
Materials and Methods
Viticultural treatments.
This study was conducted in a commercial V. vinifera L. cv. Tempranillo vineyard (clone 43 grafted onto 110R rootstock) in Ollauri, La Rioja, Spain (lat. 42°31′N; long. 2°49′W, 527 m) during 2007 and 2008. Vines were planted in 1996 in a clay-loam soil at a spacing of 2.70 m x 1.15 m with 3220 vines per hectare. The training system was vertically shoot-positioned (VSP), with each vine spur pruned to six spurs and 12 nodes. Vines were not irrigated during the growing season. Shoots were trimmed once at the end of July, before veraison.
The experimental design compared five treatments: (1) nondefoliated control; (2) manual removal of the first eight basal leaves prebloom, at stage 19 (Coombe 1995) (Man-PB); (3) manual removal of the first eight basal leaves at fruit set, at stage 27 (Coombe 1995) (Man-FS); (4) mechanical defoliation at prebloom (Mec-PB); and (5) mechanical defoliation at fruit set (Mec-FS). Laterals, if present, were not removed during manual defoliation. Prebloom treatments were performed on 29 May and 13 June and fruit-set defoliation was conducted on 15 June and 4 July in 2007 and 2008, respectively. Mechanical leaf removal was conducted with a tractor-mounted, pulsed-air leaf remover (Collard, Bouzy, France), which operates by blowing compressed air with enough force to tear off a whole leaf or sections of leaf blades. The machine was driven at ~0.5 km/hr and removed the leaves around the basal 60 cm of foliage, in the fruiting zone. The leaf remover operated in two passes, one on each side of the canopy. In each experiment, treatments were arranged in a completely randomized design that consisted of five replicates of 20-vine plots for each treatment. Within each replicate plot, five vines were randomly chosen and tagged one month before bloom, and for each vine, a representative shoot was also randomly labeled for subsequent detailed measurements. The basal cluster of each labeled shoot was also tagged.
At harvest, for each tagged vine, total leaf area was assessed using a leaf disc technique (Smart and Robinson 1991). All main and lateral leaves on tagged shoots were separately removed and weighed. One hundred discs (2-cm diam) were cut from these leaves and weighed. Disc weights were compared with the weights of main and lateral leaves, allowing main and lateral leaf area per shoot to be assessed. Total leaf area (TLA) per shoot was then calculated as the sum of the main and lateral leaf areas of the shoot. Total leaf area per shoot and the number of shoots per vine were used to estimate total leaf area per vine. For yield assessment, all clusters per tagged vine were weighed and counted and yield per vine was determined. In the laboratory, for each tagged basal cluster, berry number per cluster, cluster weight, and visual presence/absence of Botrytis bunch rot were determined. Botrytis incidence was estimated as the percentage of affected clusters per treatment. Berry weight was determined in a 100-berry sample of all clusters per vine.
Microscale fermentations and wine analysis.
The remaining grapes from the five labeled vines per replicate were harvested and blended. The grapes were transported to the winery of the University of La Rioja and stored for 12 hr at 4.5°C. Microscale wine fermentations were conducted as described elsewhere (Sampaio et al. 2007). Grapes were destemmed and slightly crushed using a motorized grape crusher (Enomundi, Zaragoza, Spain). Sulfur dioxide was added at a rate of 60 mg/kg and musts were inoculated with yeast (Saccharomyces cerevisiae; Uvaferm 71B, Lallemand, Montreal) at a rate of 20 g/hL. Fermentation temperature was maintained between 27 and 31°C. Alcoholic fermentations were completed after 7 days, but extended maceration was allowed for 8 more days. After fermentation, wines were manually racked and pressed and no malolactic fermentation was allowed. For each microfermentor, the free-run and pressed wine fractions were blended and bottled.
Sensory descriptive analysis
Sensory analysis of Tempranillo wines was conducted by a panel using descriptive analysis (Lawless and Heymann 1998). In both seasons, the tasting panel consisted of 15 members with an average age of 34 years. Descriptive analysis was conducted six months after completion of fermentation. Each season, the panelists attended four training sessions (90 min each session), where they reviewed the definitions of the sensory vocabulary describing wine aroma attributes. At the beginning of the first training session, panelists were asked to generate a set of aroma descriptors using Tempranillo wines from the 2007 and the 2008 harvests, which had not undergone malolactic fermentation, which allowed for the compilation of an unlimited list of descriptors. Later in the training sessions, panelists were presented with aroma standards typical of Tempranillo young wines and asked to evaluate them and discuss any modification, addition, or rejection of standards. Additionally, in the course of training, 12 samples of 2007 and 2008 Tempranillo wines were evaluated and the panelists were asked to identify and/or generate any additional terms. As the training sessions continued, the list of descriptors was refined to include only terms that reappeared in several of the wines, ending with a list of eight to nine attributes (Table 1⇓). For the formal evaluation sessions, standard references, made fresh daily, were evaluated at the beginning of each session before panelists rated the specified wines. Individual aroma attributes were rated on a continuous 9-point scale anchored at the ends with 0 and 9, indicating absence of that specific aroma and very high intensity, respectively.
Geometric means (GM) were calculated to determine the importance of descriptors and to represent the response of the entire panel. Each GM expressed the frequency as which a descriptor is reported by a panel adjusted by the intensities assigned to it and was calculated as GM = √(F × I). F is the number of times the descriptor was mentioned with a score different from zero divided by the total number of times that descriptor could be mentioned, expressed as a percentage. I is the sum of the intensities given by the whole panel for a descriptor divided by the maximum possible intensity for this descriptor, expressed as a percentage (ISO 1994).
All sessions were conducted at the tasting room at the University of La Rioja at 22°C. Wines (30 mL) were presented in three-figure coded wineglasses, at 18°C, with six wines presented per session in a randomized order. Each wine sample was presented twice during the evaluation sessions.
Statistical analysis.
A combined analysis of variance was performed using the Infostat professional 2007 statistical package (Córdoba, Argentina). Differences between treatments were evaluated using a priori contrasts (p < 0.05). Dunnett’s t-test (Dunnett 1955) was used to demonstrate significant differences between each defoliation treatment and the control at p = 0.05.
Results
Yield components and leaf area.
Of the four defoliation treatments, early leaf removal significantly reduced yield per vine in both years, with an average decrease of 23% less than the control. Prebloom leaf removal reduced yield more than fruit-set intervention, and the yields from the prebloom manual and mechanical treatments were lower than those of the control in both seasons. In 2007, defoliation conducted pre- and postbloom reduced basal cluster weight and number of berries per cluster (Table 2⇓), while in 2008 only the prebloom treatment produced lighter basal clusters with fewer berries (Table 3⇓). Mechanical defoliation was more effective in reducing yield, cluster weight, and number of berries than manual removal at either stage. Berry weight was not affected by early defoliation in either year, and only mechanical leaf removal at fruit set in 2007 resulted in smaller berries than the control.
The curtailment in yield, together with a favorable recovery of leaf area by the vine following defoliation, resulting in total leaf area similar to that of nondefoliated vines, led to increased leaf:fruit ratios in the defoliated vines. Total leaf area/yield (TLA/yield) range from 32% to twice the control in 2007 and 2008. As with yield reduction, the greater enhancements in leaf:fruit ratio were for the prebloom and mechanical treatments. Mechanically defoliated vines had smaller total leaf areas than manually defoliated vines.
Total rainfall was consistently higher from May until the end of the season in 2008 (Figure 1⇓). Weather conditions may have triggered the greater Botrytis incidence in 2008, especially for the control and Man-PB (Tables 2⇑, Table 3⇑). Prebloom and fruit-set defoliation helped to reduce Botrytis infection to almost none, especially in the two mechanical treatments (Table 3⇑).
Descriptive analysis.
Early leaf removal led to changes in the aroma profile of the wines in both seasons, although the extent and direction of the changes differed between years. In 2007, there were differences among treatments (p < 0.05) in six of the nine aroma attributes evaluated: strawberry-red fruit, blackberry, banana, gummy, violet, and licorice (Table 4⇓). In 2008, only four descriptors were significantly different among treatments: strawberry-red fruit, violet, cut grass, and dried fruit (Table 5⇓). In both years, the panelist factor was a significant source of variation, a typical outcome in descriptive analysis studies, as judges use different parts of the scale. Judges are trained to be consistent with each other in ranking wines for each descriptor but not necessarily to give them the same score. In terms of consistency, the treatment x judge interaction was only significant for cut grass in 2007 and gummy in 2008, but these attributes exhibited differences among treatments.
In 2007 the contrast for control vs. defoliated, which grouped all four defoliation treatments, was significant for strawberry-red fruit, banana, violet, and licorice. However, only wines made from vines mechanically defoliated at fruit set exhibited lower scores than the control for some of these attributes. Likewise, differences were encountered for all aroma descriptors except fresh flowers, cut grass, and mint between the two methods of defoliation, with the mechanical treatments given lower scores than the manual ones. In 2008, the wines obtained after early leaf removal were different than the control in strawberry-red fruit and dried fruit aromas. However, if only the prebloom treatments are considered, higher scores for violet and cut grass were also given to the wines made from defoliated vines.
There were significant regressions between the intensity of several aroma attributes and certain viticultural parameters. In 2007, violet, licorice, and fruity descriptors of strawberry-red fruit, blackberry, and gummy were positively correlated to yield at different levels of significance (Figure 2A, B⇓). The same fruity attributes did not correlate with yield in 2008 (data not shown). When the average intensity ratings for the fruity descriptors were plotted against total leaf area/yield, strawberry-red fruit, blackberry, and gummy decreased as the leaf:fruit ratio increased (p < 0.05) in 2007 (Figure 3⇓), but there was no correlation in 2008 (data not shown). In addition, the average scores of certain aroma attributes were compared to the Botrytis incidence in both seasons (Figure 4⇓). While no significant correlations were observed in 2007 (data not shown), in 2008 strawberry-red fruit and violet tended to decrease as the percentage of Botrytis increased and dried fruit was enhanced (p < 0.05) (Figure 4⇓).
Principal component analysis was used to examine the effect of the different defoliation treatments using aroma descriptors that showed differences by ANOVA in 2007 and 2008 (Figure 5⇓). In 2007, PC1 explained 94.4% of the variation in the data and all the aroma descriptors were located on the positive side. This component separated the treatments with mechanical defoliation from treatments with manual defoliation and the control. PC2 explained just 3.6% of the variation in the data and ranged from violet character at the positive end to strawberry-red fruit at the negative end.
In 2008, PC1 explained 76.8% of the variation in the data and PC2 explained 21.7% (Figure 5⇑). Of the four aroma attributes plotted, only dried fruit was on the negative side of PC1. Cut grass and violet were very close in the upper right quadrant of the map, while strawberry-red fruit was located in the lower right quadrant. PC1 separated the wines from the control (nondefoliated) vines on the negative side from the wines from early defoliated vines. PC2 separated prebloom leaf removal wines, higher in violet and cut grass, from fruit-set defoliation wines.
The relative frequency (F%), relative intensity (I%), and geometric mean (GM%) of the aroma descriptors in Tempranillo wines from different defoliation treatments in vintages 2007 and 2008 are shown. In 2007, the most frequently cited descriptors across all defoliation treatments were blackberry and strawberry-red fruit (between 78.8% and 100%) (Table 6⇓). Their frequency was higher than that of the control except for fruit-set mechanical defoliation (Mec-FS). Licorice was also cited more frequently than the control for all defoliation treatments except mechanical leaf removal at fruit set. The Man-FS wine had all descriptors except banana cited at higher frequencies than the control. In 2008, the most frequent attributes were also strawberry-red fruit and blackberry (85.7 to 92.8%) and their overall frequencies across the four defoliation treatments were higher than those of control. The frequency of dried fruit in this season was also quite high (88.1%) for prebloom mechanical defoliation (Mec-PB), although lower than that of the control (95.2%). Higher frequencies than those of the control were also observed for gummy and violet in all defoliation treatments. In general, licorice and black pepper-spicy descriptors were less frequently cited for the defoliated wines but the opposite was true for cut grass.
The relative intensity (I%) of the aroma descriptors strawberry-red fruit and blackberry had the highest values across all treatments in both seasons, although in 2008 the highest relative intensity for the control was attributed to dried fruit. Like F% and I%, the highest geometric means (GM%) in both vintages were found for strawberry-red fruit and blackberry for all defoliation treatments in both seasons. The same was observed for the control wines in 2007, although in 2008, dried fruit and blackberry had the highest GM%.
Discussion
The physiological mechanism underlying early leaf removal is based on the fact that basal leaves are the main source of assimilates at flowering and so are primary determinants of fruit set (Caspari and Lang 1996, Poni et al. 2006). Thus, reduced number of berries per cluster and yield per vine is expected. The present results confirm these findings, as yield per vine was greatly reduced and both berry number per cluster and cluster weight tended to decrease in early-defoliated vines in both seasons.
Crop control was best achieved by prebloom defoliation, since fruit-set defoliation was only effective in significantly reducing yield when it was mechanically performed. These outcomes coincide well with those previously reported in Graciano and Carignane (Tardaguila et al. 2010). However, this finding contrasts with previous findings that manual defoliation at prebloom and fruit set led to decreased crop yield at both timings (Poni et al. 2006). The same level of defoliation (eight primary basal leaves removed) was used, but laterals were removed as well. This additional defoliation may have compromised the availability of photosynthates for the inflorescence. The importance of laterals as photoassimilate net exporters has been widely demonstrated (Vasconcelos and Castagnoli 2000).
The effectiveness of mechanical defoliation in reducing yield, cluster weight, and number of berries per cluster was demonstrated both pre- and postbloom in both seasons. Mechanical leaf removal by air blowing at high pressure may tear off some parts of leaf blades. Moreover, the machine might have blown away some inflorescences at prebloom or recently set berries at fruit set. The consequence of mechanical blowing on both leaves and inflorescences may be a further decrease in yield, as observed in this study. Additionally, the leaf-blower machine might have also damaged or removed any lateral shoots already growing in the basal zone, which were retained in the manual treatments. The effects of the air-blowing leaf-removal machine were greater than those observed on Sangiovese, after using a leaf-plucker machine (Intrieri et al. 2008). The two passes in the present work compared with the single pass in the other study and the different operating principle of the leaf removers may account for the different responses observed.
The effect of early defoliation on berry weight was very uneven, even for the same cultivar. Berry weight has decreased in pot- and field-grown Sangiovese (Poni et al. 2006), remained unaltered in Sauvignon blanc (Bledsoe et al. 1988) and Sangiovese (Intrieri et al. 2008), and increased in Barbera and Lambrusco (Poni et al. 2009). In our study, no change in berry weight was observed in Tempranillo except for after mechanical defoliation at fruit set in 2007. A decrease in berry size following leaf removal, resulting from lower cell numbers within each berry plus a reduction in the final size of these cells, has been postulated (Petrie et al. 2000). However, other factors such as the photosynthetic recovery of the vine after leaf removal (Poni et al. 2006) and the hastening of assimilates translocation toward the cluster (Quinlan and Weaver 1970) may contribute to compensatory berry growth. Additionally, the sudden and extended sunlight exposure and/or temperature of the fruit, caused by early leaf removal, might positively impact cellular growth in the berry, counteracting carbohydrate limitation (Poni et al. 2006). Pericarp and exocarp cell division are sensitive to temperature in Tokay berries (Kliewer 1977). Reducing the number of berries per cluster would also contribute to compensatory berry growth, leading to unchanged berry weight as compared to an unthinned control. However, reduced berry weight in cv. Graciano because of early defoliation has been reported, even when berries per cluster were significantly restrained (Tardaguila et al. 2010).
Leaf recovery, coupled with reduced yield, increased total leaf area (TLA)/yield values with respect to the control, especially in prebloom defoliated vines. Similar enhancements of the leaf:fruit ratios were observed in Barbera and Lambrusco (Poni et al. 2009). Another important outcome deriving from early defoliation was reduced Botrytis incidence, especially in 2008. Moreover, larger effects were observed for the mechanical treatments, further supporting the use of mechanical leaf removal as a cost-effective alternative technique. The reduced number of berries per cluster, leading to looser clusters, together with improved cluster exposure induced by early defoliation contributed to the higher rot tolerance of defoliated vines. Other studies have also documented leaf removal, both manual and mechanical, as effective in controlling Botrytis bunch rot of grapes due to improved air circulation and fruit exposure (Gubler et al. 1991, Zoecklein et al. 1992).
Yield reduction by early defoliation seems to have been a primary factor in altering the aroma of the wines, as indicated by significant, positive regressions for most aroma descriptors in 2007. Similarly, positive correlations between aroma intensity of certain fruity attributes in Cabernet Sauvignon wines and buds per vine, leading to increased yields, have been reported (Chapman et al. 2004). Conversely, higher intensity of fruity and spicy aromas was correlated with reduced yield in Pinot noir wines (Reynolds et al. 1996). Differences in the reproductive-vegetative balance of the vine may exert a great influence on grape aroma. Here, the average intensity of some fruity aromas decreased as TLA/yield increased. Higher leaf:fruit ratios would promote the synthesis of secondary metabolites such as polyphenols and aroma compounds. On the other hand, the similarity in TLA at harvest in defoliated and nondefoliated vines suggests that internal canopy shading could inhibit synthesis of aroma compounds, detected only at high TLA/yield ratios. However, increased cluster exposure and canopy porosity in early-defoliated Graciano and Carignan vines were reported (Tardaguila et al. 2010). Whether the increased TLA/yield results in reduced synthesis of aroma compounds or in synthesis of alternative aromatic substances with higher perception thresholds requires further study. Nevertheless, no correlations between average intensity of aroma descriptors and yield or TLA/yield were found in 2008, indicating a more complex scenario, where other factors may also play an important role. Among these factors, the timing of defoliation, altered sunlight exposure and cluster microclimate, vintage effect, and Botrytis incidence could have an important effect on the aroma properties of the wines.
Synthesis of most secondary metabolites responsible for aroma in grapes and wines, either as volatile compounds or aroma precursors, starts after fruit set (Hashizume and Samuta 1999, Kalua and Boss 2009). Moreover, the volatile aroma compound profile (terpenes, benzene derivatives, esters, aldehydes, and alcohols) changes both qualitatively and quantitatively throughout berry development—an evolution highly dependent on enzyme activity (Kalua and Boss 2009). Likewise, any viticultural practice conducted at different timings from fruit set to harvest could potentially have an impact on the grape and hence wine aroma profile by influencing the regulation of pathways for synthesis of various volatile compounds.
One effect of early defoliation is earlier (around bloom) improvement of leaf and cluster light exposure than in classical defoliation, typically conducted between fruit set and veraison. There have been many studies on the effects of leaf and cluster sunlight exposure and temperature on wine sensory properties and on the concentration of several classes of aroma compounds in grapes and wines, such as norisoprenoids, methoxypyrazines, and glycosylated flavor precursors (Arnold and Bledsoe 1990, Reynolds et al. 2007). Before veraison, increased light exposure promotes the formation of carotenoids (the precursors of norisoprenoids) and reduces methoxypyrazine synthesis (Ryona et al. 2008), although there is some ambiguity in literature (Hashizume and Samuta 1999).
After veraison, increased sunlight exposure seems to boost the breakdown of carotenoids to norisoprenoids (Ristic et al. 2007) and the synthesis of free and bound monoterpenes (Reynolds and Wardle 1989, Zoecklein et al. 1998), but the effect on methoxypyrazine degradation is not fully understood (Hashizume and Samuta 1999, Ryona et al. 2008). As a result, more exposed canopies have been linked to less vegetative wines (Arnold and Bledsoe 1990) with increased fruity, floral, and variety-dependent tropical aromas (Reynolds et al. 2007). In the present study, the increase in cluster sunlight exposure by leaf removal did not lead to wines with more fruity and floral aromas than control wines in 2007, but did in 2008. Similar interseasonal inconsistencies in the sensory outcomes of Cabernet Sauvignon wines undergoing the same pruning treatments each season have been observed (Holt et al. 2008).
In the present work, the vintage effect was further confirmed by the geometric means (GM%), since in 2008, the GM values of fruity and floral aromas were higher for all defoliation treatments than in the control. It was dry and hot in 2007, while 2008 was rainy and cooler. These differences in weather may account for some of these discrepancies.
Another vintage effect is Botrytis rot incidence. No Botrytis infection occurred in 2007. In 2008, Botrytis incidence in nondefoliated vines was ~15% and ranged from 2 to 7% in defoliated vines. Botrytis rot has been linked to increased concentrations of certain rot organism metabolites, such as glycerol, acetic acid, gluconic acid, and ethanol (Zoecklein et al. 1992). The presence or increased concentrations of these compounds might suppress the perception of some fruity and floral aromas, as observed in 2008, or enhance the perception of other aromas such as dried fruit. Aromas and flavors can interact via masking or inhibition effects in which an increase in one (group of) characters often causes a lower rating for others (Chapman et al. 2004).
Another critical factor, not addressed in this study, is cultivar. Apart from different responses to viticultural treatments among cultivars, a genetic inconsistency among grape varieties has also been reported in relation to terpene production postveraison and in late-ripening stages (Kalua and Boss 2009). A deeper understanding of the individual contributions of each of the discussed issues above in grape aroma production and wine perception is certainly required.
Conclusions
This study confirms the effectiveness of manual and mechanical early defoliation in yield management, leading to smaller clusters with fewer berries. Fruit health can be improved by early leaf removal through the reduction of Botrytis occurrence. Sensory differences in wine aroma attributes between control and defoliation treatments were observed, although inconsistent trends between the two seasons were also noted, showing a vintage effect. Yield, leaf:fruit ratio, and Botrytis incidence were significantly correlated to certain fruity and floral aroma descriptors. The involvement of many individual factors related to early defoliation, such as yield reduction and timing of intervention (extent of improved sunlight exposure), which play a key role in the complex mechanisms involved in grape and wine aroma, was also shown.
Footnotes
Acknowledgments: The authors thank the Agencia de Desarrollo Económico de La Rioja and the Ministerio de Ciencia e Innovación for their financial support (ADER-2006-I-ID-00157; AGL2007-60378).
The authors acknowledge Agrupación de Bodegas Centenarias y Tradicionales de Rioja and New Holland for their assistance and thank the panelists involved in the quality descriptive analysis of the wines.
- Received October 2009.
- Revision received February 2010.
- Accepted February 2010.
- Published online September 2010
- Copyright © 2010 by the American Society for Enology and Viticulture
Literature Cited
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