Abstract
Bloom (20 mg/L) and various postbloom (40 to 100 mg/L) applications of gibberellic acid (GA) ± basal leaf removal (BLR) were imposed on Sovereign Coronation vines over a three-year period. GA increased yield in one of three years and berry weight in all three years, while vestigial seed development decreased in two of three years as a linear function of the concentration of GA applied. Brix was reduced linearly with increasing GA in two of three years, pH was generally unaffected, but titratable acidity decreased with increasing GA. Color intensity and anthocyanins increased relative to GA in 2002 only. Methyl anthranilate increased relative to GA in one season while total volatile esters also increased with increasing GA. Treatments involving 40 mg/L GA led to higher fruity and labrusca flavor, sweetness, persistence of flavor, and overall impression, as well as lower acidity and bitterness. Basal leaf removal delayed berry maturity slightly but increased light penetration into the canopy. Berries from non-GA-sprayed control treatments ± BLR were separated into several maturity categories (based on berry Brix) by sucrose buoyant density gradients and were thereafter subjected to sensory evaluation. Increased berry maturity was associated with decreased berry weight and titratable acidity, and increased color intensity, anthocyanins, phenols, methyl anthranilate, and total volatile esters. Principal component analysis coupled with discriminant analysis suggested that soluble solids ≥17 Brix was associated with sweetness, fruity, labrusca, and overall impression.
Several table grape cultivars are prone to visual, chemical, or physiological characteristics that result in a decrease in their quality and value. The formation of vestigial seeds in the normally seedless table grape Sovereign Coronation (Patricia x Himrod, Summerland, 1966) (Denby 1977) and frequent premature harvesting have become significant factors in the market value and production of this cultivar. In Ontario and British Columbia, increased planting of the cultivar has resulted in an emphasis on developing various cultural and chemical methods to surmount these problems. Gibberellins have been effective in the promotion of seedlessness in seeded grapes (Dry and Smart 1986, Fukunaga and Kurooka 1988, Motomura and Ito 1972) and the suppression of vestigial seed development in normally seedless grapes (Halbrooks and Crovetti 1989, Reynolds and De Savigny 2004). In addition to ensuring seedlessness, the distinctive aromatic, flavor, and textural components of the cultivar need to be maintained.
Gibberellic acid (GA) has been used not only to increase berry and cluster size and weight (Lynn and Jensen 1966, Weaver 1960, Wolf and Loubser 1992) but also to decrease compactness of tight clusters by either lengthening the rachis (Shaulis 1959) and/or by berry thinning (Lynn and Jensen 1966). There have also been reports of GA applications impacting soluble solids negatively (Singh et al. 1978, Weaver 1958) and positively (Lynn and Jensen 1966); reducing titratable acidity (Weaver 1958) or slightly increasing it (Nijjar and Bhatia 1969); increasing (Blaha 1963) or decreasing (Lee et al. 1986) color; and improving firmness (Singh et al. 1978) of grapes.
Inadequate fruit maturity at harvest is a major concern because uniform ripening and sensory perception affect consumer acceptance. Increasing sun exposure of the clusters produces higher quality, more marketable fruit. It is therefore a common practice in many winegrape vineyards to increase sun exposure through basal leaf removal, thus allowing more sunlight to penetrate the maturing clusters and increase the enzymatic reactions within the berries responsible for malic acid degradation (Lakso and Kliewer 1975). The removal of basal leaves can also increase monoterpene flavor compounds (Reynolds et al. 1995).
Gibberellic acid has rarely been tested on Vitis labruscana in humid continental climates (Cahoon et al. 1986, Shaulis 1959). The response to GA of variables such as vestigial seed formation, fruit composition, and fruit sensory quality by V. labruscana table grapes has not been well documented. The objectives of this study were to evaluate the effects of pre- and postbloom applications of GA on yield components, vestigial seed development, fruit composition, and sensory quality; to assess impacts of basal leaf removal on berry composition and sensory attributes; and to elucidate clear relationships between berry maturity (soluble solids) and sensory quality of Sovereign Coronation table grapes.
Materials and Methods
Experimental design.
Five rows of Sovereign Coronation at Tregunno Vineyards, Niagara-on-the-Lake, Ontario, Canada, were selected for experimentation. The vines were trained to a combination modified four-arm Kniffin/Geneva double curtain system consisting of two pair of canes at 1.0 and 1.4 m height, respectively, and a horizontal cordon, spurpruned (5-node spurs), at 2.2 m height. Vines were pruned to a 30 + 10 system, whereby 30 nodes were retained for the first 0.5 kg of prunings and an additional 10 nodes were retained for each 0.5 kg thereafter. Canopies were shoot-positioned around berry set in accordance with typical Geneva double curtain training. The experimental design was a randomized complete block divided into six blocks with five GA treatments arranged in a factorialized split-plot with two canopy management treatments (control and basal leaf removal, BLR). Blocks were arranged perpendicular to the vineyard rows. The treatment replicates consisted of five-vine plots in each of the six blocks. A single five-vine post-length was included at the beginning of each row as a buffer.
The gibberellic acid (GA) product (Activol; Zeneca Ltd., Fernhurst, UK) contained 0.1 g GA/g material. Treatments were a control (to which water was applied) and an application of 20 mg/L GA at 15 to 20% bloom followed by one of 40, 60, 80, or 100 mg/L BA at both 14 and 28 days postbloom (referred to as GA40, GA60, GA80, and GA100, respectively). The individual clusters were sprayed until runoff using a 10-L Solo backpack sprayer. Each treatment was imposed on two plots per block (one nonleafed and one BLR), for a total of 60 vines per treatment. Gibberellic acid was applied on the following dates: 18, 25, and 25 June 2001 to 2003 (bloom); 2, 8, and 9 July 2001 to 2003 (14 days postbloom); and 16, 22, and 23 July 2001 to 2003 (28 days postbloom). These intervals of ~14 days were based on specific phenological stages: bloom, fruit set (~3 to 5 mm diameter), and bunch closure (~8 to 10 mm diameter). Basal leaf removal, consisting of removal of all leaves at the first two to three node positions at the base of all shoots to expose the basal clusters, was imposed at bunch closure on one of each of the two GA treatment replicates per block.
Canopy assessment.
The impact of BLR was assessed by measuring cluster photosynthetic photon flux density (PPFD) approximately one week before commercial harvest using a LI-250 quantum meter (LI-COR, Lincoln, NB). Precisely 20 clusters were selected from two plots per block from a nonleafed and BLR treatment, in each of three blocks. The light meter was placed parallel to each representative cluster. These measurements were conducted every hour for six hours on a cloudless day, initially on the east side of the canopy until solar noon followed by the west side after solar noon.
Sampling and harvest.
Random samples of 10, 75, and 150 berries were collected from each of the five-vine treatment replicates in each block two days before commercial harvest. The 10-berry samples were collected from non-BLR treatments only. Samples were placed in plastic bags and stored at −25°C for later analysis, including vestigial seed development (10-berry samples); berry weight, Brix, titratable acidity (TA), pH, color (A420, A520), anthocyanins, and phenols (75-berry samples); and methyl anthranilate (MA) and total volatile esters (TVE) (150-berry samples, 2002 and 2003 only). The number of clusters was counted, and yields were recorded for each vine using an electronic scale. Cluster weights were calculated from these data. Berries per cluster were calculated from the cluster weight and berry weight data. Harvest dates were 22 to 23 Aug 2001, 25 to 28 Aug 2002, and 3 to 5 Sept 2003.
Fruit samples of ~10 kg each were collected at commercial harvest from all GA treatments in three of the six blocks in 2002 (±BLR) and 2003 (non-BLR treatments only) and were stored for less than 7 days in plastic-wrapped harvest bins at 4°C for later sensory analysis. An additional 10 kg of fruit was collected from each of the non-GA-sprayed control and BLR plots in blocks 1 to 3 for an associated fruit maturity study.
Vestigial seed number per berry.
The 10-berry samples were removed from the −25°C freezer before analysis for vestigial seeds. Berries were thawed before being sliced in half with a razor blade and seeds were removed with tweezers. The seeds were divided into immature (green) and mature (brown) categories and all five-vine treatment replicates remained separate from one another. Seeds were allowed to dry for 24 hr to achieve a dry seed mass. The seed mass was then measured using an analytical balance to the nearest 0.001 gram.
Berry analysis for Brix, TA, and pH.
Before analysis, each 75-berry sample was weighed on an electronic scale to determine mean berry weight and then placed into a 250-mL beaker and heated at 80°C for one hour in a water bath to redissolve tartrates that precipitated during freezing. The juice was extracted using an Omega 500 fruit juicer, solids were removed by vacuum aspiration, and clear juice was retained for analysis. Soluble solids (Brix) were measured using an American Optical Abbé refractometer (model 10450; AO Corp., Buffalo, NY) with temperature correction. The pH was measured with an Accumet pH meter (model AB15; Fisher Scientific, Mississauga, ON). Titratable acidity was measured with a 5.0-mL aliquot of juice using a PC titrate automated system (Man-Tech, Guelph, ON) with standardized 0.1 N NaOH.
Berry analysis for color and anthocyanins.
A 25-mL aliquot of each clear juice sample was centrifuged at 8500 rpm for 10 min using an IEC Centra CL2 centrifuge (International Equipment, Needham Heights, MA). The clarified juice was then filtered through a 0.45-μ HV Durapore syringe membrane filter (Millipore Corp., Bedford, MA). Color hue and intensity were determined by measuring absorbance of the centrifuged juice at 420 and 520 nm wavelengths using a 10-mm glass cuvette and an Ultro-spec 1000E UV/Vis spectrophotometer (Pharmacia Biotech, Cambridge, UK). Hue and intensity were then calculated using the following formulae: hue = A420/A520; intensity = A520 + A420. Anthocyanins were measured using the pH shift method (Metivier et al. 1980). Required buffer solutions were prepared as follows: pH 1.0 buffer: 0.2 M KCl + 0.2 M HCl; pH 4.5 buffer: 1 M sodium acetate + 1 M HCl. The buffers were adjusted to the appropriate pH with HCl and NaOH. Two aliquots of centrifuged juice were diluted 1:9 with either the pH 1.0 or pH 4.5 buffer in test tubes and allowed to react in the dark for one hour. The absorbance of the samples was determined using a 10-mm glass cuvette and an Ultrospec 1000E UV/Vis spectrophotometer at 520 nm. Anthocyanin concentration was calculated as malvidin chloride-3-5-diglucoside using the following formula: total anthocyanins (mg/L) = (pH 1.0 A520 – pH 4.5 A520) x 255.75.
Berry analysis for MA and TVE.
The 150-berry samples were removed from the −25°C freezer several hours before analysis and thawed. Samples (100 g) were homogenized in a blender for 30 sec, and duplicate 50 g samples were collected in 250-mL beakers. The homogenate was placed in a distillation flask to which a round-bottom steam distillation flask and a condensing column were connected (Lurex, Vineland, NJ). The first 100 mL of distillate was collected in a volumetric flask within 15 min and stored at 4°C.
Methyl anthranilate was determined using a fluorometric method adapted from Casimir et al. (1976), described in detail by Fuleki (1982). The MA standard curve was prepared from several solutions ranging in concentration from 0.1 to 2.0 mg/L. The MA concentration was determined using a luminescence spectrometer model no. LS50 (Perkin-Elmer, Boston, MA), which was set at an emission at 425 nm with an 8.0-mm slit and an excitation at 335 nm with a 5.0-mm slit. Fluorescence of the distillates was read directly and concentration was determined using the standard curve.
Total volatile esters was determined using a spectrophotometric method adapted from Hill (1946), described in detail by Fuleki (1982), using a standard curve constructed from ethyl acetate solutions ranging in concentrations from 1.0 to 125 mg/L. A 20-mL aliquot of all standards and samples, in addition to a distilled water blank, was added to a 25-mL volumetric flask. Equal volumes of 6 M hydroxylamine hydrochloride and 10.5 N NaOH were mixed and held in an ice bath; 2.0 mL of this solution was added to each flask and allowed to react for 5 min before 1.0 mL of concentrated HCl was added. Thereafter, 1.0 mL of 1.11M ferric chloride was added and brought up to volume with 0.046 M ferric chloride. Approximately 3 to 5 mL of the sample mixture was discarded and gas bubbles were removed via two or three repeated vacuum purges. Flasks were mixed vigorously after addition of each reactant and between each vacuum purge. The absorbance was then measured using a 10-mm glass cuvette in an Ultrospec 1000E UV/Vis spectrophotometer at 540 nm, and the concentration was thereafter read from the standard curve.
Maturity study: Sucrose buoyant density separation.
Sucrose solutions, ranging from 15 Brix (15 g sucrose per 100 g solution) to 21 Brix, were made using different concentrations of laboratory grade sucrose in distilled water as described by Singleton et al. (1966). Solutions were checked several times daily (by refractometer) to ensure the concentration of soluble solids (Brix) was maintained within ±0.1 units. Sound, undamaged berries from the representative treatments (nonleafed and BLR) from the non-GA control were removed from the rachis using a razor blade. The berries were initially placed in the lowest concentration solution (15 Brix); all floating berries were removed and washed in a distilled water solution, dried, and stored at 4°C for sensory analysis. Berries that sank were then placed in the solution of next highest concentration until buoyancy. Once all the berries from a cluster were separated based on buoyancy, the number of berries per class was recorded.
Berry samples from each Brix class in each treatment replicate were weighed on an electronic scale to determine mean berry weight (2002 only). A 20-berry subsample from each Brix class in each treatment replicate was placed in a zip-lock bag and stored for less than 7 days at 4°C before sensory analysis. The remainder of each sample was then further subdivided into two 50-g samples, one of which was used for measurement of TA, pH, A420, A520, anthocyanins, and phenols and the other for MA and TVE determination. Specifics of chemical analysis were as previously described.
Sensory analysis.
Sensory analysis was performed on clusters from all GA treatments (2002 and 2003) ± BLR (2002 only) and on berries from the GA control (2002 and 2003) ± BLR treatments (2002 only). Clusters (GA study) and berries (maturity study) were stored for less than 7 days at 4°C until evaluation. The evaluation panel was comprised of 10 students and professors from the Cool Climate Oenology and Viticulture Institute. The initial sensory scorecard was based upon those used by Cliff et al. (1996). In the first training session, judges were provided with several clusters representative of the study and a prototype scorecard containing prospective visual and flavor descriptive terms. All terms were familiar to the judges and therefore specific sensory standards were not prepared. During the second training session, the judges agreed upon all descriptors (such as labrusca, fruity, acidity). In the third training session, a trial evaluation was established to determine the accuracy within the panel and reproducibility of each judge. During formal sensory evaluation, the treatments were randomized before being evaluated, and no two judges received the treatments in the same order. The GA treatments, which consisted of individual clusters, were evaluated for visual, textural, flavor, and hedonic attributes. Each treatment from three of six blocks was evaluated twice. The evaluation was determined using a 100-mm line scale in Compusense software (Compusense Inc., Guelph, ON) under controlled environmental conditions and natural light.
The same sensory panel evaluated the maturity classes, using the same texture, flavor, and hedonic attributes. Panelists received two berries from each of the Brix classes. As with the GA samples, each maturity class within treatment from three of six blocks was evaluated twice. Evaluations were made under controlled conditions, including red light to prevent panelists from using color to discriminate between treatments.
Statistical analysis.
SAS statistical software (SAS Institute, Cary, NC) was used to analyze data. Analysis of variance was used for all yield, berry, and canopy data, as well as sensory analysis. The general linear models procedure (PROC GLM) was used to demonstrate significant differences among treatments. Linear, quadratic, cubic, and quartic trends were ascertained using single degree-of-freedom polynomial contrasts on the equally spaced GA treatments. Duncan’s test was used for separation of treatments at p ≤ 0.05, whereas Dunnett’s t-test (Dunnett 1955) demonstrated significant differences from the unsprayed control at α = 0.05. Principal component analysis (PCA) and discriminant analysis were completed for sensory evaluation results in 2002 to identify attributes contributing to the variation between treatments. PCA was not performed on the 2003 data since the BLR treatments were not assessed sensorially; hence a smaller data set with fewer variables was available for analysis.
Results
Gibberellic acid study.
Yield components.
The application of GA increased yield slightly in one of three years (see Table 1⇓). The yield data in 2002 displayed a quadratic (parabolic) trend relative to the concentration of GA, whereby the GA60 treatment increased the yield over the control by 17% and was the only treatment different from the control. Although yield was positively impacted by GA, clusters per vine decreased linearly with increased concentrations in two of three seasons, although the GA60 was higher than the control in 2002. Increased GA concentration provided a linear increase in mean cluster weight, in 2002, and all treatments were different that season from the control. Mean cluster weights in GA treatments increased by up to 10% compared to the control treatment. Number of berries per cluster was reduced slightly by increasing GA concentration in 2001, but berries per cluster were not affected by treatments in 2002 and 2003. Mean berry weight increased linearly with increasing concentrations in all three seasons. The GA60 treatment was not different from the unsprayed control in 2002, but the other three GA treatments that season were different from the control. Gibberellic acid had no apparent trend on weight of cane prunings (vine size) during the experiment.
Vestigial seeds.
No immature (green) seeds were detected in 2001 (see Table 2⇓). There were quadratic trends in the number of green seeds per berry in 2002 and 2003, but no GA treatment reduced green seed number. Mature (brown) seed number linearly decreased with the increasing concentration of GA in 2001 and 2002. Postbloom GA concentrations >60 mg/L reduced brown seeds relative to the control in 2001, while both the GA60 and GA100 treatments were different from the control in 2002. In 2003 there were considerably fewer mature seeds present, and the trend was quadratic; no GA treatment contained fewer seeds than the control. As with seed number, green seed weight displayed quadratic trends in 2002 and 2003 with respect to increased GA concentration; no GA treatment was different from the control. Brown seed weight showed linear decreases in 2001 and 2002 with increasing GA. All GA treatments reduced brown seed weight in 2001, and the GA60 and GA100 treatments were lower than the control in 2002. Mean brown seed weight was considerably lower in 2003; the data followed a quadratic trend, and no GA treatment reduced weight relative to the control.
Berry composition.
A decreasing quadratic trend with increasing GA concentration was observed in berry soluble solids for all three seasons (see Table 3⇓). In both 2001 and 2003, all GA treatments were lower than the control, whereas in 2002, GA60 had the lowest Brix and was different only from GA100. Titratable acidity followed quadratic (parabolic) trends in 2001 and 2003 and a decreasing linear trend with increasing GA concentration in 2002. Three treatments (GA40, GA60, GA80) exceeded the control in 2001, and GA60 and GA80 were greater than the control in 2003. The two highest concentrations had lower TA than the control in 2002. There were no obvious patterns in the pH data despite apparent linear and quadratic trends as well as significant differences between treatments in two of three years.
Color and phenols.
Hue also followed no consistent trends with respect to GA; it decreased linearly (2002) but increased quadratically (2003) (see Table 3⇑). The increased GA concentration decreased the hue in three treatments (GA40, GA80, GA100) in comparison to the unsprayed control in 2002, and three treatments (GA40, GA60, GA100) increased hue in 2003. Color intensity followed a pattern opposite that of hue; it increased linearly and quadratically with increasing GA in 2002, and all treatments were different from the unsprayed control. In 2003, this trend was reversed, and two treatments (GA60, GA100) were significantly less than the control. The trends in anthocyanin concentration followed those of intensity; they demonstrated a primarily linear increase with increasing GA in 2002, and three of four GA treatments exceeded the control. In 2003, anthocyanins decreased linearly with increasing GA, and all GA treatments were exceeded by the control. Phenolics, which were measured in 2003 only, decreased linearly with increasing GA, and three of four GA treatments were exceeded by the control.
Aroma compounds.
There was no estimable trend shown in MA concentration in 2002, although differences among treatments were demonstrated (see Table 4⇓). None of the GA treatments exceeded the control, but GA40 and GA100 had highest MA, while GA60 and GA80 led to lowest berry MA. The pattern changed in 2003, whereby linear and quadratic (parabolic) trends were found, and the GA40 and GA60 treatments exceeded the control. Total volatile esters increased linearly with increasing GA concentration in 2002 and 2003 and additionally showed a quadratic trend (Table 4⇓). For TVE, the GA80 and GA100 exceeded the control in 2002 in terms of TVE; three of four GA treatments had higher TVE than the control in 2003.
Sensory analysis. 2002 season.
The application of GA appeared to influence the perception of a few sensory attributes (see Table 5⇓). Many of the trends were second-order polynomials or above, and hence interpretation was not straightforward; moreover, the magnitude of effect was not large. Uniformity and intensity of color both followed inverse parabolic trends, whereby the GA60 treatment was lowest and reduced uniformity and intensity of color relative to the control. Skin thickness followed a similar trend, except both the GA60 and GA80 treatments were lowest. Labrusca (foxy) flavor followed a parabolic pattern whereby the GA40 and the GA60 treatments enhanced labrusca flavor, with GA40 exceeding the control. The GA40 treatment resulted in highest fruity flavor and sweetness, although the cubic and quartic trends were not readily interpretable, and none of the GA treatments differed from the control. Acidity and astringency followed cubic and parabolic trends, respectively, whereby GA40 and GA60 were lowest, but no treatment differed from the control. Persistence of flavor followed a cubic trend in which GA40 was highest and GA80 was lowest; again, no GA treatments differed from the control.
Sensory analysis. PCA 2002.
Principal components 1 and 2 explained 73.2% of the variation in the data set (see Figure 1⇓). In general, sweetness, labrusca, fruity, overall juiciness, skin friability, initial juice release, overall juiciness, and overall impression were oriented along PC1 and were all highly correlated. In contrast, acidity, astringency, bitterness, skin thickness, flesh firmness, and uniformity and intensity of color were highly correlated with each other but inversely correlated with the aforementioned attributes. Low (GA40) GA applications had a tendency to be associated with sweetness, overall impression, labrusca, and fruity eigenvectors; four of six eigenvalues from these treatments were located to the right of PC2. In addition, many of the control samples were associated with similar attributes to that of low GA concentrations, although some treatment replicates fell into the quadrant that included bitterness and astringency. Higher GA concentrations (GA80 and GA100) tended to be associated with uniformity and intensity of color, skin thickness, flesh firmness, bitterness, and acidity; 9 of 12 eigenvalues from these treatments were located to the left of PC2. The samples from the control and intermediate spray treatment (GA60) had inconsistent patterns. The BLR treatments also did not appear to follow any pattern.
Sensory analysis. 2003 season.
The application of GA influenced the perception of several attributes (see Table 6⇓). In general, the GA40 treatment appeared superior to the others in terms of color intensity and uniformity, juiciness, fruitiness, labrusca flavor, sweetness, persistence of flavor, and overall impression, whereas the GA60 treatment was lowest in color intensity and uniformity, attractiveness, and overall impression. Specifically, intensity of color, uniformity of color, attractiveness, fruity, sweetness, and overall impression displayed either linear or quadratic trends, whereby these attributes decreased relative to increasing GA concentration. The GA40, GA60, and GA80 GA treatments all differed from the control in terms of intensity of color, and GA40 and GA60 differed on the basis of uniformity of color. Cluster attractiveness followed an inverse parabolic relationship with GA concentration, whereby the GA60 treatment was lowest; all but the GA40 treatment were lower than the control. Skin friability displayed no estimable trends, but the GA40 treatment was lowest. Similarly, juiciness showed no clear trends, but the GA40 treatment was highest, and only the GA60 was lower than the control. Fruity flavor followed a linear trend, with the control and GA40 treatments displaying highest intensity, and the GA60 was lower than the control. Labrusca flavor was highest in the GA40 treatment. The higher concentrations of GA led to lower sweetness and higher acidity.
Effects of basal leaf removal.
Light microclimate.
Throughout the 6-hr period, BLR vines consistently maintained higher cluster PPFD values than the control treatment (Table 7⇓). Basal leaf removal increased cluster PPFD over the control by 90% from 1200 to 1300 hr and from 1400 to 1500 hr, by 50% from 1100 to 1200 hr, and by 36% from 1300 to 1400 hr.
Yield and fruit composition.
Basal leaf removal had no impact on any of the yield components (data not shown). Vine size was inexplicably increased very slightly by BLR in 2003 (0.22 kg control versus 0.26 kg BLR; p ≤ 0.01). There were no GA x BLR interactions throughout the three years of the trial.
Basal leaf removal increased Brix slightly in the three years of the study, while both TA and pH were reduced (see Table 3⇑). Hue and intensity were reduced slightly in one of two years, while anthocyanins were concomitantly increased in one season by BLR. Methyl anthranilate was not impacted in 2002 or 2003 (data not shown), but TVE was reduced by BLR in 2003 (11.49 mg/L control versus 9.49 mg/L BLR; p ≤ 0.0001). As with yield components, there were no significant GA x BLR interactions throughout the trial.
Sensory analysis.
There were no specific effects of BLR on sensory attributes in 2002, with the exception of a slight increase in initial juice release in the BLR treatments (data not shown). There were no GA x BLR interactions. Based on this paucity of sensory impact, BLR treatments were not assessed in 2003.
Maturity study.
Berry weight and composition.
The mean berry weight decreased linearly in 2002 with increasing maturity level (see Table 8⇓). Noteworthy segregations were elucidated between several of the maturity classes; important divisions occurred between 17.0 and 17.5 Brix, 18.5 and 19.0 Brix, and 19.5 and 20.0 Brix. Berry weights were not determined in 2003. Titratable acidity decreased linearly both seasons with the increasing maturity classes, while pH showed increasing linear and quadratic trends in response to increasing maturity level. Hue showed a slight decreasing linear trend in both seasons in response to the increased maturity level, whereas color intensity increased linearly. As with berry weight, noteworthy segregations were elucidated between the maturity classes in 2002 between 17.5 and 18.0 Brix, 18.0 and 18.5 Brix, and 19.5 and 20.0 Brix; in 2003, large increases in intensity occurred between 18 and 19 Brix and between 20 and 21 Brix. Anthocyanins showed a linear increase both seasons with increased maturity. There was no trend in MA concentration in 2002, but MA increased linearly with increasing maturity in 2003. Total volatile esters decreased linearly with increasing maturity class in 2002 but showed an opposite (and perhaps more expected) trend in 2003.
Berry maturity distribution: Implications of BLR.
Basal leaf removal decreased the number of mature berries within a cluster and increased the number of immature berries (see Table 9⇓). In 2002, clusters that had been subjected to BLR had more berries in the 15.0 and 16.0 Brix classes, and less berries in the 18.0, 18.5, and 19.0 Brix classes compared to the control. The control displayed a more normal (“Gaussian”) distribution of berries, whereas BLR demonstrated a flatter curve that was skewed to the left. In 2003, this pattern was generally repeated; there were more berries in the BLR clusters in the 14, 15, and 16 Brix categories and fewer in the 21 and 22 Brix categories.
Sensory analysis. 2002 season.
Berry maturity appeared to influence the sensory evaluation of various attributes (Table 10⇓). In 2002, initial juice release and overall juiciness generally decreased with increasing maturity level, but also demonstrated a quadratic trend for both attributes. No differences were found in fruity flavor, but labrusca flavor demonstrated a quadratic (parabolic) trend, with highest levels in the 17 to 18 Brix categories. Perceived sweetness increased linearly with increased maturity and also showed a quadratic trend. Acidity, bitterness, and astringency were perceived to decrease linearly with increased maturity. Overall judge impression increased with increasing maturity of the berries. Basal leaf removal impacted four attributes in 2002 (data not shown): reductions in skin friability (p ≤ 0.01) and overall impression (p ≤ 0.05) and increases in bitterness (p ≤ 0.0001) and astringency (p ≤ 0.001). No maturity x BLR interactions of consequence were observed.
Sensory analysis. PCA 2002.
Principal components 1 and 2 explained 71.2% of the variation in the 2002 data set (see Figure 2⇓). In general, flesh firmness, skin thickness, sweetness, fruity, persistence, labrusca, and overall impression were all highly correlated. In contrast, astringency, bitterness, acidity, initial juice release, skin friability, and overall juiciness were also highly correlated with each other but inversely correlated with the above attributes. Generally, berries in the range of 15 to 17 Brix had a tendency toward astringency, bitterness, acidity, initial juice release, skin friability, and overall juiciness. Berries 17.5 Brix and above had a tendency toward flesh firmness, skin thickness, sweetness, fruity, persistence, labrusca, and overall impression. Stepwise discriminant analysis (data not shown) determined four attributes that explained the greatest variation among maturity classes. Perceived acidity and sweetness showed the greatest variance; however, the initial juice release and fruity attributes were also associated with differences among classes. As per analysis of variance results, BLR did not appear to alter the projected sensory descriptors from the lower classes to the higher classes. However, within a maturity class, BLR samples tended toward the lower maturity sensory descriptors, whereas the control samples tended toward the attributes described by more mature berries.
Sensory analysis. 2003 season.
In 2003, increasing maturity level led to linear increases in fruity, labrusca, sweetness, and overall impression as well as concomitant decreases in skin thickness, acidity, bitterness, and astringency (Table 11⇓).
Discussion
Influence of GA.
Yield components.
Several yield components responded to application of GA. Berry weight demonstrated a linear increase as a function of the concentration of GA that was applied, which corresponds to the concomitant increases in cluster weight. Increases in berry and cluster weights have previous been obtained through multiple applications of GA on numerous seedless cultivars over unsprayed controls (Lynn and Jensen 1966, Singh et al. 1978, Weaver 1960). In addition, single gibberellin sprays applied 20 to 21 days postbloom also resulted in increased berry and cluster weights in Bhokri, Gros Colman, and Anab-e-Shahi (Dass and Randhawa 1968). The increased berry weight attained through postbloom GA3 applications were a consequence of stimulation of cell division (Motomura and Ito 1972) followed by the increased accumulation of components in subsequent growth stages, hence increasing cluster weight and yield. These factors gave rise to an increased yield per vine in this trial that was previously observed by Bondok et al. (1985).
Despite the increases in yield over the three seasons, the number of clusters per vine decreased overall and relative to GA concentration in 2002 and 2003. The overall reductions in cluster number (and vine size) were likely a consequence of drought conditions in 2001 and 2002. Weaver (1960) observed decreases in shoot and cluster counts (hence yield) resulting from previously applied gibberellins. Dry and Smart (1986) correlated GA3 application with the induction of primary bud necrosis, hence a decrease in clusters and yield the following season.
Vestigial seeds.
Gibberellin application decreased the incidence of vestigial seed formation in 2001 and 2002. The response to GA by green seed number and weight was generally inconsistent; however, the number and weight of brown seeds decreased linearly as a function of the increasing GA concentration. The reduction in true and vestigial seeds has been reported by Dry and Smart (1986) for seeded cultivars, Fukunaga and Kurooka (1988) for Kyoho, Halbrooks and Crovetti (1989) in Orlando Seedless, and Reynolds and De Savigny (2004) in Sovereign Coronation. However, the required concentration of GA has varied among cultivars. Concentrations used throughout this experiment appeared to provide the reduction in vestigial seeds that has been previously reported; even though the seeds were not fully removed, a decrease in overall seedlessness was observed. The number and weight of vestigial seeds appears to be a function of water relations. As with our previous study (Reynolds and De Savigny 2004), vestigial seed formation was relatively high in the dry seasons of 2001 and 2002, and generally low in 2003, in which there was abundant precipitation. Gibberellic acid was largely ineffective in 2003. These results are consistent with Kimura et al. (1996), who indicated that high temperatures and low rainfall rendered GA treatments on Muscat Bailey A table grapes ineffective in inducing seedlessness.
Berry composition.
Berry soluble solids response to GA applications was generally inconsistent. Brix decreased slightly in 2001 and 2003, which coincides with Singh et al. (1978) and Weaver (1958); however, Brix increased at the highest GA concentration in 2002 relative to the GA60 treatment, which is in general agreement with and Lynn and Jensen (1966). The TA decreased linearly in two of three years with the increasing spray treatments in accordance with Weaver (1958), while pH was largely unaffected. The decrease in hue and the increase in color intensity and anthocyanin concentration are generally consistent with reported results; Blaha (1963) reported increases in color with GA applications, whereas Lee et al. (1986) reported decreases in color. In general, the consensus in the literature suggests that GA delays fruit maturity. Wolf and Loubser (1992) associated delayed maturity of Sultana and Waltham Cross with GA-treated vines. Nonetheless, the observed increases in Brix, color components, and MA and TVE and the corresponding decrease in TA suggest an enhancement in berry maturity.
Sensory analysis.
Principal component analysis suggested that treatments involving postbloom GA applications of 80 and 100 mg/L tended toward sensory attributes such as acidity, astringency, bitterness, skin thickness, flesh firmness, and uniformity and intensity of color. In 2002, the measured increases in color intensity (A420 and A520) and anthocyanin concentration corresponded to the perceived uniformity and intensity of color, but the increased acidity perception inexplicably contrasted the measured decrease in TA. Moreover, the firmness response to GA in 2002 is in agreement with Singh et al. (1978), who demonstrated increased firmness with multiple GA applications. Generally, in 2002, PCA suggested that lower GA applications were associated with labrusca, sweetness, and overall impression. The unsprayed control tended toward highest labrusca and sweetness, which corresponded to the chemical data.
Influence of maturity.
Berry weight and composition.
Berry weight decreased linearly with the increase in maturity (measured as Brix), possibly resulting from evaporation and desiccation of the more mature fruit. The increase in soluble solids was paralleled with a linear decrease in TA and a linear increase in pH, coinciding with previously reported data (Winkler 1958). Also, the linear increases in color intensity and anthocyanin concentrations were observed as the maturity was increased with inconsistent fluctuations in hue. These compositional changes were reported by Smart (1987) in relation to increased cluster exposure during the maturation process.The flavor components MA and TVE also responded linearly to increased maturity. However, TVE, although a linear relationship, demonstrated large fluctuations among the classes in both seasons.
Sensory analysis.
Principal component analysis suggested that increased maturity categories tended toward sensory attributes such as fruity, persistence, labrusca, sweetness, and overall judge impression. This correlation between perceived sweetness and overall judge impression has previously been reported by Winkler (1958). Generally, less mature berries were associated with astringency, bitterness, acidity, and initial juice release. Analysis in 2002 demonstrated the distinction between two perceived categories: 15.0 to 17.0 Brix and 17.5 Brix and above, as defined by soluble solids concentration. Winkler (1958) stated that “no single constituent of the grape functions independently of other factors in its effect on palatability,” which was demonstrated through sensory analysis. Thus, the segregation of berries based solely on soluble solids may be an insufficient measure of maturity.
Implications of leaf removal.
Cluster PPFD measurements demonstrated an enhanced light environment for BLR fruit. The implications of this improved fruit environment are primarily light-induced temperature effects and usually include decreases in TA because of degradation of malic acid (Lakso and Kliewer 1975), increases in anthocyanins and other phenolic components (Crippen and Morrison 1986), and increases in aroma compounds (Reynolds et al. 1995). In this trial, BLR treatments increased Brix and anthocyanins slightly, with concomitant decreases in TA and pH. However, the main implication of BLR from the maturity component of the study was, surprisingly, a delay in fruit maturity when berry distribution was considered. Clusters from the BLR treatment contained more immature berries than the nonleafed treatment. This pattern is in accordance with Kliewer and Lider (1968), who demonstrated a greater uniformity of maturity in shaded Thompson Seedless fruit compared to sun exposed fruit, as a result of more consistent ripening conditions. Berry soluble solids decreased as a result of BLR as previously reported by May et al. (1969) and Kliewer (1970). The most probable explanation was the decreased photosynthetic area resulting in decreased carbohydrates available for the ripening period as suggested by Smart (1987) in addition to the decreased leaf area per unit of cluster described by May et al. (1969).
Conclusions
Application of GA treatments had moderate impact on yield components, vestigial seed formation, berry composition, and sensory attributes of Sovereign Coronation. All GA treatments reduced the development of vestigial seeds in two of three years. Many responses to increasing GA concentration were linear, with the 100 mg/L postbloom GA treatment producing the highest berry weight and lowest TA, along with high concentrations of color and aroma components. The 40 mg/L postbloom treatment resulted in the higher sensory attributes. Application of GA would be beneficial in reducing vestigial seeds, maintaining or increasing basic berry composition, and increasing sensory perception for consumers.
Buoyant density separation was used to delineate berry maturity classes. A clear relationship was elucidated between maturity class and the sensory quality. However, the berry maturity data are in contrast to the expectation that leaf removal would enhance berry maturity and sensory attributes. Leaf removal expanded the distribution of berries to include a greater percentage of immature berries, thus delaying maturity.
Footnotes
Acknowledgments: This paper represents work included in the Undergraduate Thesis of J. Roller (2003). Authors wish to thank Philip Tregunno, Tregunno Farms, for his cooperation. Efforts of the many sensory panelists are also acknowledged.
Financial assistance from the Natural Sciences and Engineering Research Council and the National Research Council of Canada is hereby acknowledged.
- Received March 2005.
- Revision received August 2005.
- Revision received October 2005.
- Copyright © 2006 by the American Society for Enology and Viticulture