1 Introduction

Grape cultivation is one of the most remunerative farming enterprises in India. Thompson Seedless and its clones (Tas-A-Ganesh, Sonaka, 2A Clone) are the varieties grown popularly in hot tropics comprising parts of Maharashtra, Telangana and northern Karnataka (Shikhamany, 2001). Berry thinning is essential to produce loose to well-filled clusters with bold berries in these varieties. Berry thinning is achieved with blanket sprays of GA₃ prior to bloom in temperate viticulture, but the growers in tropical region of India have resorted to manual thinning, because GA₃ sprays were found to be ineffective in berry thinning.  Manual thinning is labour intensive and time consuming. Delayed thinning is not effective enough in increasing the size of retained berries (Winkler et al., 1974; Coombe, 1960). Moreover, manual thinning often leaves unseen injuries to the retained berries which get infected by weak pathogens like Alternaria, Botryodiplodia and Rhizopus resulting in post harvest decay (Chadha and Shikhamany, 1999). Hence, chemical thinning is very essential. Main reason for the ineffectiveness of blanket sprays of GA₃ in tropical conditions is the lack of uniformity in the stage of flowering as a consequence of uneven bud break. In turn, presence of canes of uneven diameter in a vine is the basic reason for uneven bud break.  Early and more uniform bud break was observed in relatively thin canes (Reddy and Shikhamany, 1990; Shikhamany and Manjunath, 1992). Berry thinning with GA is mediated through its pollinicidal effect (Weaver and Mc Cune, 1960; Weaver, 1961). Hence the GA₃ sprays are to be given prior to pollination and fertilization. According to Turner (1972), the effective stage is three to one day prior to initiation of bloom. A field trial was, therefore, conducted during the fruiting season of 2013-14 and 2014-15 to study the effects of removal of uneven canes in inducing uniform bud break, consequently uniform flowering and differently given GA₃ sprays in reducing the cluster compactness in Thompson Seedless grapes and its clones namely Tas-A-Ganesh and 2A Clone.

2 Materials and Methods

These investigations were carried out during cropping season of 2013-14 and 2014-15 on six year old Thompson Seedless grapevines and its clones (Tas-A-Ganesh, 2A Clone) in farmers’ vineyards around Nashik district (Maharashtra, India). Tas-A-Ganesh is bud sport identified by Late Vasantrao Arve in his vineyard at Borgaon, Maharashtra (India) and 2A clone was identified at Kearney experimental Station, University of California, Davis, USA. The experimental vines were grafted on Dogridge rootstock and trained to extended Y trellis. Distance between rows and within rows was 2.70 and 1.50 m, respectively. Vines were pruned for fruiting in the second week of October and grapes were harvested in the first week of March. All the vines were subjected uniformly to pre-pruning defoliation by spraying ethrel @ 1500 ppm and hydrogen cyanamide application to the buds @ 1.5 per cent for promoting bud break; and GA₃ sprays @ 10 and 15 ppm, respectively at parrot green stage and a week later for cluster elongation.

The field experiment was designed to answer the following questions.

1. Whether removal of un-uniform canes from a vine can improve the uniformity in flowering?

2. Whether increase in uniformity in flowering can improve the efficacy of GA₃ in reducing the cluster compactness?

3. Whether less number of GA₃ sprays at higher concentration or more number at low concentration is more effective?

4. Whether the clones of Thompson Seedless respond to berry thinning treatments similar to it?

5. Whether grape yield and quality will be affected by cane removal and varyingly applied GA₃?

Experiment in each vineyard was laid out in a Factorial A x B x C randomized block design with the following treatments replicated thrice.

Factor A-Season: S1 - 2013-14 and S2 - 2014-15

Factor B-Varieties: V1 - Thompson Seedless, V2 - Tas-A-Ganesh and V3 - 2A Clone

Factor C-Treatments (Removal of unevenly thick canes coupled with GA₃ sprays)

T1 - Cane removal coupled with three sprays of GA₃ @ 20 g a.i./ha each.

T2 - Cane removal coupled with two sprays of GA₃ @ 30 g a.i./ha each.

T3 - Retention of all canes coupled with three sprays of GA₃ @ 20 g a.i./ha each.

T4 - Retention of all canes coupled with two sprays of GA₃ @ 30 g a.i./ha each.

T5 - Control (Growers’ practice of retaining all the canes and spraying GA₃ @80 g a.i./ha at 50 per cent bloom

The first spray of GA₃ was given at a stage approximately three days prior to initiation of bloom, repeating on alternate days. GA₃ at specified dose was sprayed with blower assisted/electrostatic sprayer irrespective of the volume of spray solution.

Observations recorded

Observations were recorded on five canes tagged in five vines selected at random in each replication/ treatment

Canes/vine: Number of canes left on the vine after forward pruning and cane removal.

Cane diameter: Diameter at the middle length of each cane was measured and the average diameter was calculated.

Uniformity of bud break: Number and position of buds breaking on each selected cane was recorded every day from the 5^th to 12^th day after pruning. The day on which highest number of buds broke was taken as the standard (D-day) and given 100 score for each bud. For one day deviation in bud break from the D-day; either early or late, was given 75 for each bud, 50 for each bud deviating by two days and 25 for each deviating by 3 days. The sum of scores was divided by the total number of broken buds and expressed as ‘per cent uniformity of bud break’

Uniformity of flowering: The stage of inflorescence development specified for giving the first spray of GA₃ for thinning was used as the reference. Observations were recorded on the number of inflorescences attaining this stage from the 30^th day after pruning on the selected canes. The day on which highest number of panicles attained this stage was taken as the standard (D-day) and given 100 score for each bud. For one day deviation from the D-day; either early or late, a score of 75 was given for each panicle, 50 for each deviating by two days and 25 for each deviating by 3 days. The sum of scores was divided by the total number of panicles and expressed as ‘per cent uniformity of flowering’.

Cluster Compactness Index: Derived by multiplying the number of berries per cm of the total length of rachis by the mean berry diameter in a cluster. Berry count and total length of rachis were recorded after removing the berries in five clusters selected at random from each plot. Mean diameter of five berries selected from each cluster was used to arrive at the index. Clusters with > 35 index were classified as compact, 31-35 well filled, 25-30 loose and <25 straggly.

Total length of rachis: Sum of the length of main rachis and all its branches measured in cm.

Berries/cluster:  Average number of berries was counted in five selected clusters.

Berry diameter: Average diameter of 25 berries, was measured at middle length of the berry using callipers.

Yield/vine: Average yield of 10 vines in a plot was recorded in kg at harvest.

Cluster weight: Mean weight of five clusters selected at random from each plot was calculated.

Total soluble solids content: Soluble solids content was determined in ^O B using hand refractometer in the juice extracted by crushing the 25 selected berries

Titratable acids content (TSS): Determined by titrating an aliquot of 10 ml juice against 0.1N NaOH using phenolphthalein indicator and expressed as gram equivalent tartaric acid in 100 mL juice.

Statistical analysis: Data were analyzed in factorial A x B x C (2 x 3 x 5) design with eight treatment combinations and three replications. Where, A-was the season, B-varieties and C-treatments.  Percentages of uniformity in bud break and uniformity of flowering were transformed respectively into square root and arcsine values for statistical analysis.

3 Results and Discussion

Variation in the response to removal of un-uniform canes and GA₃ treatments by Thompson Seedless and its clones in different years in reducing the cluster compactness and sustaining the yield and quality have been elucidated in this chapter.

3.1 Cluster compactness

Cluster compactness was not different in different years. It was less in 2A Clone compared to other varieties, which were at par. Compactness was reduced by GA₃ sprays, either thrice @ 20 g a.i./ha or twice @30 g a.i./ha coupled with either cane removal or retention of all canes, compared to a single spray of GA₃ @ 80 g a.i./ha at 50 per cent bloom (control). While three sprays of GA₃ @ 20 g a.i./ha did not reduce compactness compared to two sprays @ 30 g a.i./ha in cane-retained vines, but it reduced in cane-removed ones (Table 2). Compactness was less in 2A Clone compared to others in 2013-14, but not in 2014-15 (Table 2a). Reduction in compactness with treatments was observed in 2013-14 but not in 2014-15. Over the years, as also in 2014-15, spraying GA₃ thrice @ 20 g a.i./ha resulted in less compactness than spraying twice @ 30 g a.i./ha, but in 2013-14 both were at par in reducing the compactness (Table 2b). Varieties differed in their response to treatments. While treatments did not reduce the compactness compared to control in 2A Clone, they reduced it in Thompson Seedless and Tas-A-Ganesh. While cluster compactness did not differ among treatments in 2A Clone, it differed in other varieties. Within cane removal, three sprays of GA₃ @ 20 g a.i./ha resulted in less compactness compared to two sprays @30 g a.i./ha in Thompson Seedless, but not in Tas-A-Ganesh. When three sprays were considered, cane removal resulted in less compactness compared to cane retention in Tas-A-Ganesh, but not in Thompson Seedless (Table 2c). Although effect of season was not significant and cluster compactness was less in 2A Clone compared to Thompson Seedless, compactness in the latter variety in 2013-14 was at par with that in former in 2014-15 (Table 2d).

As mentioned earlier, cluster compactness is a function of total rachis length and the number and diameter of berries in a cluster. Number of berries per cm length of the rachis is the recognized measure of cluster compactness (Chadha and Shikhamany, 1999), but berry size also contributes to cluster compactness. At a given number of berries/cm length of rachis, a cluster with berries of 20 mm diameter will be more compact than the one with 16 mm berry diameter.

3.2 Rachis length

Total length of rachis/cluster was more in 2014-15 compared to 2013-14. It was highest in Thompson Seedless followed by 2A Clone and Tas-A-Ganesh with significant differences among varieties. Rachis length was not affected by either cane removal or GA₃ sprays (Table 2). The ideal stage of application of GA₃ for cluster elongation was between three and one day prior to full bloom (Turner, 1972). Hence, the GA₃ sprays given 2-3 days prior to full bloom were not effective in cluster elongation.  Rachis length was less in Tas-A-Ganesh in 2014-15, but was more in 2013-14 when compared to other varieties. Rachis length was more in Thompson Seedless than in 2A Clone in 2024-15, but not so in 2013-14 (Table 2e). While treatments did not influence the mean length of rachis, cane thinning coupled with two sprays of GA₃ @ 30 g a.i./ha and the control resulted in the longest rachis in Thompson Seedless. Whereas, in 2A Clone, retention of all canes coupled with three sprays of GA₃ @ 20 g a.i./ha increased the rachis length more than the control. Inconsistent effect of GA₃ sprays could be due to variation in varietal response to GA₃ just prior to bloom (Christodoulou et al., 1968).

3.3 Berries/cluster

Less number of berries/cluster is a desirable character with respect to cluster compactness. Number of berries/cluster was less in 2013-14 than in 2014-15. Clusters of Thompson Seedless had least number of berries followed by Tas-A-Ganesh and 2A Clone with significant differences. Treatments had little effect in reducing the berry number/cluster (Table 2). Non significant differences among treatments indicated that the growers’ practice of spraying GA₃ @ 80 g a.i./ha at 50 per cent bloom stage (control) was as effective as either spraying thrice @ 20 g a.i./ha or twice @ 30 g a.i./ha just before bloom.  Berries/cluster were more in 2A Clone compared to other varieties in 2014-15. Whereas, in 2013-14 Thompson Seedless had more berries than 2A Clone but was at par with Tas-A-Ganesh. Although berries/clusters were more in 2014-15 compared to 2013-14 in 2A Clone, they were at par between years in Tas-A-Ganesh, but more in 2013-14 in Thompson Seedless (Table 2g).

Effect of blanket sprays with GA₃ in reducing the berry number/cluster depends on the uniformity in the ideal stage of panicle required for their efficacy.

3.4 Uniformity in flowering

Flowering was more uniform in vines in 2014-15 compared to 2013-14 and less uniform in Tas-A-Ganesh compared to other varieties. It was less uniform when uneven canes were removed (Table 1). Uniformity in bud break did not manifest in uniformity in flowering. This could be due to differential rate of flower development influenced by genotype (Negi and Randhawa, 1974; Daulta and Bakhshi,1970) and cane diameter, which also varied with season, variety and cane removal.  Mean uniformity in flowering is the composite mean of varieties and treatments. Effect of cane removal needs to be assessed in interaction with variety and season. Interaction between season x variety was apparent in Tas-A-Ganesh. Although uniformity in flowering was less in this variety in 2013-14, it was at par with other two varieties in 2014-15 (Table 1d). Cane removal reduced the uniformity in 2013-14 but not in the later cropping season (Table 1e). Cane removal reduced the uniformity in Thompson Seedless but not in 2A Clone. Effect of cane removal was not consistent in Tas-A-Ganesh (Table 1f). Wide variation in the uniformity in flowering was observed due to the interaction effect of season x variety x cane removal in 2013-14 when compared to 2014-15. Cane removal or retention coupled with three sprays of GA₃ @ 20 g a.i./ha reduced the uniformity in Thompson Seedless and Tas -A- Ganesh in 2013-14, and only in Thompson Seedless in 2014-15 but in none of the seasons in 2A Clone. Since, GA₃ sprays given at the end of flower development have no role in the uniform development of flowers, the variation in the uniformity in flowering can be attributed to the variety, season and uniformity in cane thickness brought in by cane removal. Effect of environment (Christensen, 1969) and varietal variation (Negi and Randhawa, 1974) in flower development have been well documented. Reduction in uniformity in flowering could also be attributed to less cane density (number/vine at uniform spacing) as a result of cane removal and also to the effect of uniform pre bloom GA₃ sprays given for cluster elongation.

Uniformity in flowering depends mainly on uniformity in bud break, which in turn depends on the uniformity in the thickness of canes in a vine. Bud break was found to be faster in thin canes compared to thick canes (Reddy and Shikhamany, 1990; Shikhamany and Manjunath, 1992). Hence, removal of uneven canes was attempted to induce uniform flowering mediated through uniform bud break in a vine.

Table 1 Effect of cane regulation and GA3 treatments on vine growth characters Note: Means super-scribed with the same alphabets within column do not differ significantly at P=0.05

Table 1a Season x Variety effect on canes/vine

Table 1b Season x Variety effect on Cane diameter (mm) Note: Means super-scribed with the same alphabets do not differ significantly at P=0.05

Table 1c Season x Treatment Effect on Cane diameter (mm)

Table 1d Season x Variety effect on uniformity in flowering (Arc sine values)

Table 1e Season x Treatment Effect on uniformity in flowering (Arc sine values)

Table 1f Variety x Treatment effect on uniformity in flowering (Arc sine values)

Table 1g Season x Variety x Treatment effect on uniformity in flowering (Arc sine values) Note: Means super-scribed with the same alphabets do not differ significantly at P=0.05

3.5 Uniformity in bud break

Bud break was more uniform in 2013-14 than in 2014-15. It did not differ among the varieties or the treatments. Interaction among varieties, season and treatments also did not affect the uniformity in bud break. In spite of thicker canes in 2013-14, bud break was more uniform (Table 1). If canes in a vine are uniformly thick, bud break may be delayed but uniformly. In addition to the uniformity in cane thickness, uniformity in bud break depends on the pre-pruning defoliation, diurnal variation in temperature after pruning (Shikhamany and Manjunath, 1992) and the use of chemicals promoting bud break (Shulman et al., 1983; Williams, 1987). The effect of cane removal on inducing uniform bud break could have been masked by the growers’ practice of using ethrel for pre pruning defoliation, pruning when temperature is conducive for bud break and using hydrogen cyanamide for inducing increased and uniform bud break.

3.6 Cane diameter

Mean cane diameter, across the varieties and cane removal treatments, was more in 2013-14, compared to 2014-15. Among the varieties, it was more in Thompson Seedless compared to its clones. Cane diameter was more in vines in which the uneven canes were removed (Table 1). It implies that, mostly the under sized canes were removed. Cane diameter was influenced by the Season x Variety interaction. It was more in 2013-14 compared to 2014-15 in Tas-A-Ganesh and 2A Clone, but not in Thompson Seedless. Cane diameter was more in Thompson Seedless than in its clones in 2014-15, but not in 2013-14 (Table 1b). Treatments did not influence the cane diameter in 2013-14, but in 2014-15, cane removal treatments increased it. Mean cane diameter was although more in 2013-14 as compared to 2014-15, it was at par between the years in vines in which uneven canes were removed. GA₃ spray treatments would have not influenced the cane diameter, which was measured much earlier to spraying.

3.7 Berry diameter

Berry thinning was found to increase the size of retained berries in a cluster (Coombe, 1960; Winkler et al., 1974). Hence, berry diameter was included in the factors determining the cluster compactness in these studies. Mean berry diameter across the varieties and treatments was more in 2014-15 as compared to 2013-14. It was less in 2A Clone than in Thompson Seedless and Tas -A- Ganesh, which were at par. Treatments did not differ in their effect on berry diameter. Reason for ineffectiveness of GA₃ treatments in increasing the berry diameter is the mode of action of GA₃ and its stage of application. GA₃ increases the berry length but not its diameter. The ideal stage of GA₃ application for berry elongation is between five to ten days after full bloom (Turner, 1972). Hence, application of GA₃ just before bloom was ineffective in increasing berry diameter. The growers’ practice of using CPPU and/or homobrassinolides could have had a dominating role in increasing the berry diameter. Variation in the berry diameter among the varieties is also an indication to their variable response to growth substances. Berry diameter, within a variety, also depends on the number of berries/cluster and leaf area available/cluster (Chittiraichelvan et al., 1985). Berry diameter was more in 2014-15 as compared to 2013-14 in Thompson Seedless and Tas-A-Ganesh, but more in 2A clone than other varieties in 2013-14. It was more in Thompson Seedless than 2A Clone in 2014-15, but less in 2013-14. While, berry diameter in Tas-A-Ganesh was at par with Thompson Seedless across the seasons, it was more in Tas-A-Ganesh than Thompson Seedless in 2013-14, but more in Thompson Seedless than Tas-A-Ganesh in 2014-15 (Table 2h). While treatments did not influence berry diameter, it was more in control compared to cane removal coupled with three sprays of GA₃ @ 20 g a.i./ha in Thompson Seedless. Whereas, the latter treatment resulted in more diameter than retention of all canes coupled with three sprays of GA₃ @ 20 g a.i./ha in Tas-A-Ganesh. Retention of canes coupled with two sprays of GA₃ @ 30 g a.i./ha also increased berry diameter more than retention of canes coupled with three sprays of GA₃ @ 20 g a.i./ha in Tas-A-Ganesh (Table 2i).

Table 2 Effect of cane regulation and GA treatments on components of cluster compactness Note: Means super-scribed with the same alphabets within column do not differ significantly at P=0.05

Table 2a  Season x Variety effect on cluster compactness index

Table 2b Season x Treatment effect on cluster compactness index Note: Means super-scribed with the same alphabets do not differ significantly at P=0.05

Table 2c Variety x Treatment effect on cluster compactness index

Table 2d Season x Variety x Treatment effect on cluster compactness index

Table 2e Season x Variety effect on rachis length (cm)

Table 2f Variety x Treatment effect on rachis length (cm)

Table 2g Season x Variety effect on berries/cluster

Table 2h Season x Variety on berry diameter (mm) Note: Means super-scribed with the same alphabets do not differ significantly at P=0.05

Table 2i Variety x Treatment effect on berry diameter (mm) Note: Means super-scribed with the same alphabets do not differ significantly at P=0.05

3.8 Yield/vine

Yield/vine was more in 2014-15 compared to 2013-14. Thompson Seedless and 2A Clone were at par, but both were superior to Tas-A-Ganesh in this respect. Removal of uneven canes coupled with three sprays of GA₃ @ 20 g a.i./ha reduced the yield/vine compared to the growers practice (Table 3). Over the years, Thompson Seedless was at par with 2A Clone but in 2013-14, 2A Clone out yielded Thompson Seedless, while in 2014-15, the latter variety yielded more. Though yield/vine in Thompson Seedless was more than Tas-A-Ganesh over the years, it was at par in these varieties in 2013-14 (Table 3a). Removal of uneven canes coupled with three GA₃ sprays @ 20 g a.i./ha reduced the yield compared to control in 2014-15, but not in the previous year. Yield/vine was more in control but at par with treatment with GA₃ twice @ 30 g a.i./ha coupled with cane removal and also in the treatment with GA₃ thrice @ 20 g a.i./ha without cane removal, but was less in other treatments in 2014-15 (Table 3b). Cane removal coupled with either three sprays of GA₃ @ 20 g a.i./ha or two sprays @ 30 g a.i./ha reduced the yield/vine in Thompson Seedless but not in its clones (Table 3c). Yield/vine is a function of mean weight of the cluster and the number of clusters/vine. Hence, the variation in yield needs to be analyzed based on the variation in these factors.

Cane is the unit of productivity of a vine. Despite less cane number/vine in cane removal treatment coupled with two sprays of GA₃ @ 30 g a.i./ha compared to control, yield /vine was at par. This could be due to more number of clusters/cane. In addition to cane number/vine, number of cluster/cane also determines the yield/vine. By working back the number of clusters based on the yield/vine and mean cluster weight (Table 3) and subsequently the clusters/cane based on the canes/vine (Table 1), clusters/ cane was 1.35 in cane thinned vines but 1.01 in control. This difference could only be attributed to the favourable conditions for fruit bud formation during the vine growth season. Hence, the variations found in cane number and yield/vine in Thompson Seedless and Tas-A-Ganesh in 2014-15 cannot be attributed to the treatments imposed during the fruiting season.

3.9 Canes/vine

Canes/vine was more in 2013-14 than in 2014-15. They were more in 2A Clone than in Tas-A-Ganesh or Thompson Seedless. Latter two varieties were at par in this respect. Removal of un-uniform canes resulted in significant reduction in the number of canes/vine (Table 1). Cane number was more in 2A Clone in 2013-14 but at par with that in Tas-A-Ganesh or Thompson Seedless in 2014-15, when the former variety had more canes/vine than the later (Table 1a).

3.10 Cluster weight

Mean weight of cluster was more in 2014-15 than in 2013-14. It was more in Thompson Seedless than in 2A Clone which in turn was more than in Tas-A-Ganesh. Removal of un-uniform canes coupled with three sprays of GA₃ @ 20 g a.i./ha and retention of all canes coupled with two sprays of GA₃ @ 30 g a.i./ha reduced the cluster weight compared to control (Table 3). This could be attributed to less compact clusters and relatively (though not significantly) less number of berries/cluster in these treatments compared to control (Table 2). Cluster weight in Thompson Seedless was at par with 2A Clone in 2013-14, but more in 2014-15. It was more in 2014-15 only in Thompson Seedless but not in its clones (Table 3d). Reduced cluster weight was observed only in Thompson Seedless subjected to cane removal together with three sprays of GA₃ @ 20 g a.i./ha and also where canes were retained and GA₃ sprayed twice @ 30 g a.i./ha, but not in its clones (Table 3e).

Table 3 Effect of cane regulation and GA3 treatments on yield and quality attributes Note: Means super-scribed with the same alphabets within column do not differ significantly at P=0.05

Table 3a Season x Variety effect on Yield/vine (kg) Note: Means super-scribed with the same alphabets do not differ significantly at P=0.05

Table 3b Season x Treatment effect on yield/ vine (kg)

Table 3c Variety x Treatment effect on yield/vine (kg)

Table 3d Season x Variety effect on weight/cluster (g)

Table 3e Variety x Treatment effect on weight/cluster (g)

3.11 Total Soluble Solids content

Total soluble solids (TSS) content of berries was more in 2014-15 than in 2013-14. It was more in 2A Clone followed by Tas-A-Ganesh and Thompson Seedless in significantly decreasing order. Treatments had no effect. TSS content did not differ among the years in Tas-A-Ganesh, while Thompson Seedless had higher TSS in 2013-14 compared to the subsequent year. TSS content was more in Tas-A-Ganesh than in Thompson Seedless in 2014-15, but it was not different between these varieties in 2013-14 (Table 3f). Mean TSS content across the treatments was higher in 2014-15 than 2013-14. But, in berries treated with GA₃ twice @ 30 g a.i./ha with or without cane removal and with 20 g a.i./ha thrice and cane thinning, the TSS content did not differ between the years (Table 3g). TSS content is primarily a varietal character, often modified by the diurnal variation in temperature during the ripening period (Coombe, 1992), and is mainly controlled by the genotype x environment interaction. Treatments could influence the TSS content through their effects on cluster and berry size and yield/vine (Chadha and Shikhamany, 1999).

3.12 Acids Content

Acids content of berries was more in 2013-14 compared to 2014-15. It was more in Tas-A-Ganesh followed by Thompson Seedless and 2A Clone in significantly decreasing order. It was not affected by treatments (Table 3). While acids content was more in 2013-14 in 2A Clone, it did not differ between years in Tas-A-Ganesh, but was more in 2014-15 than 2013-14 in Thompson Seedless. Although berries of 2A Clone had less acids than the rest two varieties in 2014-15, acids content did not differ among the varieties in 2013-14 (Table 3h). While acids content was not influenced by the treatments in 2013-14, control resulted in less acids compared to three sprays of GA₃ @ 20 g a.i./ha coupled with cane removal in 2014-15. Spraying GA₃  twice @ 30 g a.i./ha with cane retention resulted in less acids content compared to either two sprays @ 30 g a.i./ha or three @ 20 g a.i./ha in cane removed vines. Cane retention coupled with either three sprays @ 20 g a.i./ha or two @ 30 g a.i./ha resulted in more acids content in 2013-14 compared to 2014-15, while other treatments did not (Table 3i). Similar to TSS, acids content is also determined by the genotype x environment interaction. Acids content generally vary inversely with TSS, because there is simultaneous reduction in acids content with increasing TSS content during the ripening of berries (Drawert and Steffan, 1966).

Table 3f Season x Variety effect on T.S.S. content of berries (oB)

Table 3g Season x Treatment effect on T.S.S. content of berries (oB)

Table 3h Season x Variety effect on acids content of berries (g/100mL) Note: Means super-scribed with the same alphabets do not differ significantly at P=0.05

Table 3i Season x Treatment effect on acids content of berries (g/100mL)

4 Conclusion

Results of the trial revealed that, retention of all canes and spraying GA₃ twice @ 30 g a.i./ha resulted in not only loose to well-filled clusters but also retained the level of yield and quality in Thompson Seedless grapes and its clones, namely Tas-A-Ganesh and 2A Clone.

Acknowledgements

The authors are grateful to S/Shri. Ashok Gaikwad, Suresh Kalamkar and Manik Patil for facilitating these studies in their vineyards. Also, thanks to the office bearers and the Chairman, Central Research Committee of the Maharashtra State Grape Growers’ Association, Pune for supporting these studies. The support given by Prof. T.S. Mungare and Shri. T.S. Shelke and the guidance provided by the Research Advisory Committee of the Association are gratefully acknowledged.

References

Chadha K.L., and Shikhamany S.D., 1999, The Grape- Improvement, Production and Post Harvest Management (ISBN: 81-85048-40-1), Malhotra Publishing House, New Delhi, India, pp. 129-130

Chittiraichelvan R., Shikhamany S.D., and Chadha K.L., 1985, Contribution of leaf area towards bunch development in Thompson Seedless grape, Indian J. Hort., 42 (3&4):156-160

Christensen P., 1969, Seasonal changes and distribution of nutritional elements in Thompson Seedless grapevines, Amer. J. Enol. Vitic., 20: 176-190

Christodoulou A. J., Weaver R. J., and Pool R. M., 1968, Relation of gibberellin treatment to fruit-set, fruit composition and vine phenology of Sauvignon Blanc vines, Proc. Amer. Soc. Hort. Sci., 92: 301-310

Coombe B.G., 1960, Relationship of growth and development to changes in sugars, auxins and gibberellins in fruit of seeded and seedless varieties of Vitis vinifera, Plant Physiol., 35: 241-250

http://dx.doi.org/10.1104/pp.35.2.241

Coombe B.G., 1992, Research on development and ripening of the grape berry, Amer. J. Enol. Vitic., 43:101-110

Daulta B.S., and Bakhshi J.C., 1970, Evaluation of vinifera varieties. I. Growth and flowering, Punjab Hort. J., 10 (1/2): 42-47

Drawert f., and Steffan M., 1966, Biochemisch-physiologische unteresuchungen on Traubenbeeren. III. Stoffwechsei von Zugefuhrten C¹⁴ verbindungen und die Bedeutung des Saure-Zucker Metabolismus fur die Reifung Von Traubenbeere, Vitis, 5: 377-384

Negi S.S., and Randhawa G.S., 1974, Improvement of grapes with special reference to tropical conditions of peninsular India, Indian J. Genet., 34A: 1268-1275

Reddy N.N., and Shikhamany S.D., 1990, Comparative efficacy of spray and dip treatments with H₂CN₂ on bud break in Thompson Seedless grape vines under tropical Indian conditions, Gartenbauwissenchaft, 55(1): 27-30

Shikhamany S.D., 2001, “Grape Production in India Grape” In: Minas K. Papademetriou and Frank J. Dent, eds., Grape production in the Asia Pacific Regions, Bangkok, Thailand: Food and Agriculture Organization of the United Nations Regional Office for Asia and the Pacific, pp. 251

Shikhamany S.D., and Manjunath G.O., 1992, Effect of hydrogen cyanamide and date of pruning on bud break, subsequent shoot growth, yield and quality in Thompson Seedless grape. In: Recent Advances in Vitic. Oenol, Proc. Intl. Symp., Hyderabad, India, pp. 181-187

Shulman Y., Nir G., Fangerstein L., And Lavee S., 1983, The effect of cyanamide on the release from dormancy of grapevine buds, Sci. Hort., 19: 97-104

http://dx.doi.org/10.1016/0304-4238(83)90049-3

Turner J.N., 1972, Practical use of gibberellin in agriculture and horticulture. Outlook on Agriculture, 1: 14-20

Weaver R.J., and Mc Cune S.B., 1960, Further studies with gibberellin on Vitis vinifera grapes. Bot. Gaz., 121: 155-162

http://dx.doi.org/10.1086/336060

Weaver R.J., 1961, Effect of gibberellin on vine behaviour and crop production in seeded and seedless Vitis vinifera,  Hilgardia, 30: 425-444

http://dx.doi.org/10.3733/hilg.v30n15p425

Williams L. E., 1987, The effect of cyanamide on bud break and vine development of Thompson Seedless grapevines in the San Joaquin valley of California, Vitis, 26: 107-113

Winkler A.J., Cook J.A., Kliewer W.M., and Lider L.A., 1974, General Viticulture. University of California Press, Berkeley, USA, pp. 138-196 & 338-370