Abstract: The effect of variation in bunch load (40, 50, 60 and 80 bunches/vine) on yield and quality components in table grapes were studied at the research farm of National Research Centre for Grapes, Pune during the year 2003-2005. The trial was conducted on five-year-old Tas-A-Ganesh grapes and was compared with vines grafted on Dog Ridge rootstock. In the grafted vines, the average bunch size was higher than own rooted vines. Higher berry diameter of 17.23 mm was recorded in grafted vines as against 16.21 mm in own rooted vines. The yield per vine in grafted vines was increased by 44.93% over own rooted vines. The total soluble solids also reduced with the increase in yield per vine. As the bunch load per vine was increased, there was reduction in quality in terms of berry diameter and TSS; however, the total yield per vine was increased.
Introduction
Grape is one of the major important fruit crop grown in India. The major produce in the country is used as table purpose and the small quantity is converted into raisin, wine and juice. The produce is exported to the markets of Europe, Chile, Holland and Middle East. To produce the quality grapes, it requires careful control of crop size to balance the amount of fruit to vegetative growth, quality fruit and adequate vine growth for consistent productivity. Excess fruit production leads to poor fruit quality and reduced vegetative growth resulting into poor yield in the coming years. Due to the continuous problems of drought and build up of salinity in the soil in the grape growing regions, the growers shifted to use of rootstock for grape cultivation. Incorrect application of cultural practices in grafted and own rooted vines may lead to negative effects on vegetative growth and fruit quality. In India, the proportion of harvested grapes having exportable quality is less than the expected. However, the remaining produce is sent to the local market. The requirement of cultural practices are different for local market and for export purpose. The grower tries to exploit the vine to the maximum extent by retaining maximum number of bunches per unit area on the vine leading to poor quality that ultimately harvest minimum quantity of exportable produce. Due to the heavy load on the vine, cluster drying from the tip is also observed in majority of the vineyards. However, controlling of yield via pruning is an important way to increase the table grapes quality (Harun Coban and Serdar Kara, 2002). As in sugar accumulation the colour of grape is also influenced by many factors like climatic conditions (Pirie and Mullins, 1977), training systems (Reynolds et al, 1994; Smart et al, 1985).
Considering these above-mentioned problems, an investigation was carried out to study the effect of different crop load so as to maintain the quality fitting into the standards for local market and also for export in Tas-A-Ganesh grapes grafted on Dog Ridge rootstock and on own rooted vines.
Materials and Methods
The experiment was carried out at the farm of National Research Centre for Grapes, Pune during the year 2003-2005. The five-year old vines of Tas-A-Ganesh, a clone of Thompson Seedless grafted on Dog Ridge rootstock and own rooted vines were selected for the experiment. Dog Ridge rootstock and own rooted Tas-A-Ganesh were planted at a spacing of 10 X 6 distance and were trained on flat roof gable system of training with 1.3 m stem height. According to the climatic condition during the year of study (data not given) there was enough rainfall with favorable weather after October pruning and the crop was considered as normal. The soil of this region is black having pH 7.75 and EC 0.46 dS/m (Sharma and Upadhyay, 2005). In the Peninsular India, double pruning and single cropping is a crop pattern followed in grapes. After harvest of crop, back pruning was performed by retaining 1-2 basal buds on the cane. Excess, weak and very vigorous shoots were removed and appropriate numbers of shoots having uniform vigour were retained on each vine under study. Since the bud differentiation takes place during 45-60 days after back pruning, shoot-thinning operation was considered to be important in point of harvesting enough sunlight by individual buds. All the vines under experiment were given uniform cultural practices such as fertilizers, irrigation and plant protection.
The fruit pruning was done during October and the vines under each treatment were cluster thinned at pre bloom to setting stage to four different crop levels of 40, 50, 60 and 80 bunches/vine to create moderate to heavy crop load on own rooted and grafted vines. The excess number of bunches were thinned out. Under each treatment of bunch load, five vines were selected for study. The experiment was designed in Factorial randomized block design (FRBD) with five replication. The details of the factors are as below.
Factor A
Plant type
| • | Own rooted Tas-A-Ganesh |
| • | Tas-A-Ganesh grafted on Rootstock |
Factor B
Bunches/vine
| • | 40 Bunches/vine |
| • | 50 bunches/vine |
| • | 60 bunches/vine |
| • | 80 bunches/vine |
To study the effect of these treatments on growth, yield and quality on grafted vines in comparison with own rooted vines, bunches under each treatment were harvested on the same date. The shoot length, shoot diameter was measured at 75th days after October pruning. When the target of approximate 180 Brix total soluble solids concentration was reached, all bunches were harvested. The harvested bunches were weighed for different characters. Harvested grape bunches were brought to laboratory for physico chemical analysis and following parameters were studied. From the lot, 100 berries were selected randomly and total soluble solids (TSS) were determined using digital refractometer (model ERMA of Japan). A drop of juice was extracted and placed on clean prism of refractometer and the lid was closed. Reading was taken directly from the scale at room temperature. The acidity was determined by described method. Ten ml of the extracted juice was titrated against 0.1 N NaOH. The remaining bunches from all the treatments were harvested and yield per vine, average berry weight, berry diameter, 50-berry weight, bunch weight and yield per vine were recorded (Winkler et al., 1974). The data was statistically analyzed as per Panse and Sukhatme (1967).
Results and Discussion
Growth Performance
The data analyzed on growth parameters is given in Table 1.
Significant differences were recorded among the plant type. The shoot growth
and shoot diameter was more in case of Tas-A-Ganesh vines grafted on Dog Ridge
rootstock as compared to the own rooted vines. Higher shoot length of 80.67
cm was recorded in grafted vines as compared to 63.5 cm in own rooted vines.
It was observed that increase in number of bunches per vine had reduced the
shoot growth. When minimum number of bunches per vine was retained, the shoot
growth was found to be higher. The reduction in number of bunches per vine might
have resulted into weakening of the sink, the bunch that resulted in increased
shoot growth. Christensen et al. (1994) also reported that increased
crop load has a negative effect on vegetative growth. However, the differences
for the interaction of bunch number and plant type (grafted vs. own rooted)
were found to be non significant. Higher shoot diameter was recorded when minimum
number of bunches were retained per vine. Increase in number of bunches resulted
into reduction in shoot diameter. This might be due to competition among bunches
for their growth resulted into weak shoot.
Bunch and Berry Characters
Berry diameter is an important quality parameter considered while exporting
the grapes. There were significant differences among the bunch load treatments
in own rooted and also in grafted vines. Overall performance of grafted vines
was found to be superior for bunch and berry characters to the own rooted vines.
Higher berry diameter was recorded in grafted vines (17.23 mm) as compared to
the own rooted vines (16.21 mm). In grafted vines, 40 bunches per vine resulted
into higher berry diameter of 18.50 mm as compared to 17.56 mm in own rooted
vines. The reduction in number of bunches per vine had increased the berry quality.
Dhillon et al. (1990;1992) also reported the improved fruit quality of
Perlette grapes by reducing the crop load either by cluster or berry thinning.
The increase in berry diameter might be due to proper utilization of food material
by bunch, the sink. These results confirm the results obtained by Hunter and
Visser (1988 b) who reported that the fruit after berry set becomes the very
large sink. The increase in bunch number reduced the berry diameter. When the
heavy crop load/vine was maintained (80 bunches) the berry diameter reduced
to the maximum. Since the grapes to be exported requires to have minimum 18
mm diameter, retention of 40 bunches seems to be ideal in grafted vines. However
for local market 14 to 16 mm berry diameter can serve the purpose in the Indian
market. The same trend was observed for 50-berry weight (Table
1). In general, 1.0 to 1.5 mm increased berry diameter was recorded on grafted
vines than on own rooted vines in a given situation.
The average bunch weigh was more in case of reduced number of bunches per vine in both the plant type. In grafted vines, higher bunch weight of 350 g was recorded when minimum number of bunches (40) were retained. The reduction in bunch weight was recorded with the increase in bunch number per vine (Table 2). Dhillon et al. (1998) also reported that increased crop load decreased the mean cluster weight in Perlette grapes.
| Table 1: | Effect of crop load on growth and berry characters in Tas-A-Ganesh grapes |
| Table 2: | Effect of crop load on bunch and quality characters in Tas-A-Ganesh grapes |
| Table3: | Effect of different crop load on yield parameters in Tas-A-Ganesh grapes |
In the grafted vines the vigour in the form of shoot growth was also found enough. The shoot vigor was also maintained in grafted vines than in own rooted vines. This might be due to the supply of available food reserve to the developing berries that has resulted into good quality form these vines. Eynard and Gay (1992) also suggested that equilibrium of crop load versus vegetative development is important for quality fruit.
Yield and Quality Characters
In grapes, berry diameter, sugars and colour are major quality contributing
parameters. Total soluble solids in berries were recorded higher at 40-bunch
load (22.16 in own rooted vines and 20.24 in grafted vines) as compared to the
maximum bunch load of 80 bunches per vine (19.92 and 18.60, respectively). Higher
TSS was recorded in own rooted vines (21.45° Brix) compared to the grafted
vines (19.610 Brix). As the yield increased by increasing the number
of bunches, there was decline in quality in terms of TSS and berry diameter
(Table 1 and 2). The berries containing
increased total soluble solids (above 20° Brix) are not preferred in the
international market. However, in the local market higher grapes containing
higher TSS is given due importance. Hence, the grapes harvested from own rooted
vines having high total soluble solids and minimum berry diameter can serve
the requirement of the local market. Significantly higher yield was recorded
in grafted vines (15.654 kg) as compared to the own rooted vines (10.801 kg).
The increase in number of bunches per vine resulted into increase in yield/vine.
Though the bunch weight was less in more number of bunches per vine treatment,
the overall yield per vine was increased due to cumulative increase in bunch
load. These results are in accordance with the results obtained by Jackson and
Lombard (1993) who reported that high yields and vigour often reduce grape quality.
Production practices used to maximize grape quality parameters or yield can
have a significant effect on the source-sink relationship of the grapevine (Williams,
1996). Availability of more number of bunches in the form of high yield delays
the maturity (Bravado et al., 1985). The yield per acre was more in case
of grafted vines (11.38 tone) than the own rooted vines (7.84 tone). The increase
in total yield with the increase in crop load was also supported with the results
obtained by Howell et al. (1991) and Reynolds (1994). This is mainly
because the shoot vigour that is required for photosynthesis and formation of
food reserve was less in own rooted vines. As the yield per vine increased with
the increase in number of bunches, the yield per acre was also increased. The
yield per acre was more in grafted vines than in own rooted vines. Maximum yield
of 11.380 tone/acre was recorded than 7.481 tone in own rooted vines (Table
3). It was observed that, with the increase in bunch load, the overall yield
per vine and also yield/acre in both the plant type was increased. The Brix
yield is said to be the important criteria for considering the yield level of
the vine. Maximum Brix yield of 2.23 was recorded in grafted vines as compared
to 1.67 in own rooted vines. The yield per vine in grafted vines was increased
by 44.93% over the own rooted vines under study.
The grapes harvested form the vine should fulfill the requirement of the consumers. For export, the bunch weighing 350 to 400 g having 18 mm and above diameter with 18 0 Brix total soluble solids is considered to be ideal. The bunch load retained as 40 bunches per vine in grafted vines has fulfilled the requirement. Hence, such type of bunch load per vine can be retained keeping in view the purpose of exporting the grapes however, the number of bunches can be increased up to 60 per vine if the produce is considered for local market. The results on bunch load and plant type revealed that under the adverse situation of soil and water, establishment of grape vineyards the vineyards on rootstock is the alternative for grape cultivation that can results in higher berry quality in terms of berry diameter, average bunch weight and yield per vine as compared to own rooted vines.