Canopy Modification Influences Growth, Yield, Quality, and Powdery Mildew Incidence in Tas-A-Ganesh Grapevine

ABSTRACT

A field trial was conducted to study effect of different canopy modifications on growth, yield, quality, and disease incidence in Tas-A-Ganesh grapevine grafted onto Dogridge rootstock. Ten-years-old vines trained to extended Y training system with three types of canopy modifications [Single Cordon Horizontal (SCH), Double Cordon Horizontal (DCH), and Four Cordon Horizontal (FCH)] were selected for study. The vines had horizontally placed cordon with vertically positioned shoot on the cordon. Results of different canopy modification demonstrated that, among the vegetative growth parameters studied, pruning weight and shoot length was significantly higher in DCH. Days to bud sprout and cane diameter had no significant influence of any of the canopy modifications studied. Significant differences were observed for leaf area index, photosynthesis rate, stomatal conductance, and transpiration rate. The vines trained to DCH had higher rate of photosynthesis. Yield per vine and number of bunches per vine was higher in FCH. Maximum total soluble solids (TSS) was recorded in SCH. Total acidity was increased with increase in cordons from SCH to FCH. Lower concentration of total acids was recorded in SCH (0.56%). We observed that as bunch load increased, TSS was reduced while total acidity was increased. The disease assessment data from different canopy modifications revealed that powdery mildew incidence was significantly increased from SCH to FCH with increase in canopy density. The results supported with concentration of lower phenols in powdery mildew-infected canopy (FCH). The results revealed that the canopy with DCH canopy modification performed better for growth and yield and reduced disease incidence.

KEYWORDS:

• Canopy modification
• photosynthesis
• yield
• quality
• Tas-A-Ganesh

Introduction

Under the tropical condition, grape cultivation is restricted to Thompson Seedless and its clones (Tas-A-Ganesh, Sonaka, Manik Chaman, etc.). In this region, the vines are pruned twice i.e., once after the harvest of fruits (foundation pruning) for development of fruitful canes and for fruit during October (forward pruning). Canopy management plays an important role in successful grape production. Depending on the soil type, vine vigor, and weather available in particular region, the vine is trained to different training system. Training a grapevine accomplishes many objectives viz., the perennial wood and canes can gets the benefit of exposure of leaf area to interception of light leading to higher yield potential; facilitate mechanization of vineyard operations; a renewal zone is formed, which ensures that the vine form is perpetuated and yield is maintained (Reynolds and Vanden Heuvel, 2009).

The leaf and shoot system of vine comprises canopy (Shaulis and Smart, 1974). Grapevine orientation in space through the training system has significant effects, particularly on light distribution through the canopy. These alterations in microclimate affect growth, yield, disease development, and fruit composition (Ferree et al., 2002). Comparative higher cost of quality grape production demands priority for its management practices (Somkuwar et al., 2014). It has been widely reported that trellis systems dividing vine canopy increase sunlight penetration, which in turn increase yield and fruit quality (Carbonneau and Casteran, 1987; Smart, 1985). Training systems used in grape vineyard can strongly influence microclimatic conditions and have received attention as they directly impact temperature, humidity, and other environmental factors (Gladstone and Dokoozlian, 2003; Reynolds and Heuvel, 2009). Canopy management includes different techniques that are applied to vineyard to change amount of leaves, shoots, and fruits in space leading to desired canopy microclimate. Canopy modifications mainly aimed at improving production potential, reduced disease incidence, and facilitate mechanization. (Travis, 1987). However, canopy modification is important factor leading to differences in allocation of carbon to fruit sink for increased fruit productivity without losing growth and developmental harmony and is major aim of grapevine canopy management (Hunter et al., 1995; Smart et al., 1985). Leaf area index (LAI) is one of the most frequently used parameters for the analysis of canopy structure and it has also been shown to be an important structural characteristic of the forest ecosystem and forest productivity (Arias et al., 2007; Beadle, 1997).

Under the tropical condition, high temperature during the fruit ripening stage affects the fruit quality. To protect the bunch, different training systems are being tried. However, the higher cost of trellises may lead to reduction in the profit. Considering these aspects, the study was conducted to evaluate different cordon modifications in Y trellis system on growth, yield, quality, and disease incidence in Tas-A-Ganesh grapevines.

Material and Methods

Experimental Site

A field experiment was carried out for four consecutive years (2010–2014) at the experimental farm of ICAR-National Research Centre for Grapes, Pune (18.32°N and 73.51°E). Ten-year-old vines of Tas-A-Ganesh grapes grafted onto Dogridge rootstock were selected for the study. The soil of this region is black having pH 7.75 and EC 0.46 dS/m. However, water used for irrigation had EC 1.8 and pH 8.3 (Sharma and Upadhyay, 2005). The vines were trained to extended Y trellis system. In the existing canopy, variations were created with increase in number of cordons i.e., Single Cordon (SC), Double Cordon (DC), and Four Cordon (FC). The orientation of the cordon was in horizontal position while the shoots were positioned vertically on the cordon. Planting of grapevine was done in North–South direction, spaced at 2.4 m between rows and 1.2 m between vines, thus accommodating 1815 vines per hectare. The vines were pruned twice in a year, once after harvest of the crop (foundation pruning) and another for fruits (fruit pruning). The vines under experiments were irrigated through drip irrigation as well as the recommended fertilizer dose was given through drips. All the recommended cultural practices were followed during the period of study. The experiment was conducted in Randomized Block Design, with three treatments replicated seven times. Five vines were selected for study under each replication.

Vegetative Growth Parameters

The observations on pruned biomass, days to bud sprouts, average shoot length, cane diameter, and total number of canes per vine were recorded during each season. The first sprouted bud with fully expanded leaf was taken as an indicator to calculate the days taken for sprouting and were recorded on day-to-day basis by visual observations. The shoot length, cane diameter, and total number of canes per vine were measured using measuring tape, digital Vernier caliper (0–300 mm RSK™, China), and manual counting, respectively.

Photosynthetic Parameters

The LAI was recorded with the help of Sunscan Canopy Analyzer made in england (Delta T Devise, England). Photosynthetic rate, stomatal conductance, and transpiration rate were recorded using Infra-Red Gas Analyzer made in USA (IRGA model Li 6400, LI-COR Biosciences, NE, USA). Matured leaves i.e., fifth to sixth from tip were used for measuring these parameters. Observations were recorded during bright sunlight at 11 am to 12.30 pm.

Yield and Yield Components

The total number of bunches per vine were recorded by manual counting. Average bunch weight (g) was calculated from average weight of 15 bunches while yield per vine (kg) was recorded at the time of harvest. Randomly selected berries from bunches at harvest were used for 50 berry weight. To measure average berry length and berry diameter, 10 berries were selected randomly from different bunches from a given replication and were measured using Digital Vernier Caliper (0–300 mm RSK™) and were expressed in millimeter.

Disease Assessment

Powdery mildew incidence was assessed in situ by visual observations. The number of leaves affected with powdery mildew infestation on a given vine was recorded under each treatment. In addition, the canes affected with powdery mildew infection at 90 days after pruning were also recorded. The infection of disease on leaf as well as on cane was recorded using 0–5 scale and expressed as percent infection as per Affeldt and Wu (2009).

Biochemical Analysis

Fresh berry samples collected were hand-pressed for extraction of juice and filtered through muslin cloth. Samples were kept at −20ºC until analysis could be performed. Ten milliliters of extracted juice was taken for estimation of quality parameters such as total soluble solids (TSS) (°Brix) and acidity (g/l) with aid of OenoFoss instrument (OenoFoss™, Millerod, Denmark). Total phenolic content in leaf was estimated by using 1 g fresh leaf sample homogenized in 80% ethanol repetitively and final volume was made up to 10.0 ml. The mixtures were sonicated for 15 min for complete extraction and centrifuged at 9,000 rpm for 10 min. The supernatants were utilized for analysis of total phenolic contents. The total phenolic contents were determined by Folin-Ciocalteu method using gallic acid as the standard (Singleton and Rossi, 1965). The total phenolic concentration was calculated from a calibration curve using gallic acid as a standard (0–10 mg l⁻¹). Data were expressed in mg·g⁻¹ gallic acid equivalent (GAE).

Statistical Analysis

Analysis of variance was performed for each variable using SAS statistical package Version 9.3 (SAS Institute, Cary, NC, USA). Least significant differences among treatments were calculated using the same software.

Results and Discussion

Effect of Canopy Modification on Vegetative Growth and Photosynthetic Parameters

Based on the pooled data, the results obtained on pruned biomass, vegetative growth parameters (shoot length and total number of canes/vine) under different training modification were varied significantly (Table 1). The highest pruning weight (4.20 kg) was recorded in double cordon horizontal (DCH) which was at par with four cordon horizontal (FCH) (3.81 kg) while lowest in single cordon horizontal (SCH) (3.24 kg). In DCH-trained vines, pruning weight was consecutively higher for years 2011–2012 to 2013–2014. It was observed that, low pruning weight in SCH-trained vines was deciphered by lower number of cordons, less number of cane leading to accumulation of less biomass. Thus, canopy modification was found to be associated with less pruning weight in SCH-trained vines. Bordelon et al. (2008) reported that increase in pruning weight might be due to increased canopy length and number of shoots per vine. Obviously factor responsible for accumulation of biomass was more in DCH and FCH. Even though, comparatively higher pruning weight in DCH than FCH might be due to relatively more open canopy leading to synthesis of more photosynthetic assimilates as effect of more exposed leaf surface area to sunlight. Gu et al. (2005) reported hand-pruned vines with bilateral cordon had greater pruning weights. However, Sabbatini et al. (2015) reported the choice of training system should be based on specific grower and vineyard needs. Due to the horizontal direction of cordons, the present system allows high levels of light interception, with bunches protected under the canopy.

Table 1. Effect of canopy modification on vegetative growth and photosynthetic parameters on Tas-A-Ganesh grapes.

	April pruning weight (Kg)					Days taken to bud sprout					Shoot length (cm)
Treatments	2010–11	2011–12	2012–13	2013–14	Pooled	2010–11	2011–12	2012–13	2013–14	Pooled	2010–11	2011–12	2012–13	2013–14	Pooled
SCH	2.85	3.40	3.60	3.10	3.24	14.06	13.80	15.31	15.00	14.54	85.23	102.05	86.93	110.10	96.08
DCH	3.05	4.80	4.30	4.65	4.20	16.10	14.18	14.42	16.30	15.25	90.23	115.20	91.05	124.78	105.32
FCH	3.25	4.20	3.80	4.00	3.81	15.03	15.20	14.21	17.00	15.36	70.50	93.40	71.71	92.35	81.99
CV %	2.21	2.52	1.42	1.42	8.86	1.84	2.58	2.21	2.21	5.62	3.73	2.18	1.98	1.98	3.93
LSD 5%	0.08	0.12	0.05	0.03	0.58	0.32	0.44	0.34	0.38	1.46	4.64	2.02	1.75	3.17	6.42
Significance	**	*	**	**	*	**	*	**	**	NS	**	**	**	**	**
	Cane diameter (mm)					Total number of canes/vine
Treatments	2010–11	2011–12	2012–13	2013–14	Pooled	2010–11	2011–12	2012–13	2013–14	Pooled
SCH	9.76	8.48	8.65	8.80	8.92	24.43	38.00	36.22	46.00	36.16
DCH	9.00	9.62	9.60	8.55	9.19	40.75	45.00	50.10	55.70	47.89
FCH	8.06	8.82	8.60	7.80	8.32	58.25	74.75	70.21	72.80	69.00
CV %	3.05	2.33	2.43	2.43	6.07	3.53	2.23	2.50	2.50	6.71
LSD 5%	0.31	0.23	0.24	0.26	0.93	1.69	1.55	1.88	1.69	5.92
Significance	**	**	**	**	NS	**	**	**	**	**
	Leaf area index					Photosynthesis rate (µmol. cm^−2 s^−1)					Stomatal conductance (cm. s^−1)					Transpiration rate (µmol. H2O m^−2s^−1)
Treatments	2010–11	2011–12	2012–13	2013–14	Pooled	2010–11	2011–12	2012–13	2013–14	Pooled	2010–11	2011–12	2012–13	2013–14	Pooled	2010–11	2011–12	2012–13	2013–14	Pooled
SCH	1.69	1.70	1.60	1.80	1.70	10.60	11.00	11.07	12.30	11.24	0.16	0.18	0.20	0.21	0.19	1.81	2.28	2.43	2.56	2.27
DCH	1.75	1.80	1.89	2.10	1.89	13.30	13.51	13.59	14.70	13.78	0.20	0.23	0.27	0.29	0.25	2.56	3.14	3.14	3.19	3.01
FCH	1.54	1.62	1.70	1.88	1.69	9.11	9.31	9.38	9.63	9.36	0.10	0.13	0.13	0.13	0.12	1.35	1.67	1.67	1.72	1.60
CV %	2.42	2.82	2.30	2.30	4.09	4.37	3.89	3.93	4.11	2.49	4.18	7.97	3.26	6.78	8.22	2.86	2.86	2.05	5.90	4.15
LSD 5%	0.04	0.06	0.04	0.05	0.12	0.60	0.44	0.48	0.53	0.49	0.01	0.03	0.01	0.01	0.03	0.08	0.08	0.09	0.15	0.16
Significance	**	**	**	**	**	**	**	**	**	**	**	**	**	**	**	**	**	**	*	**

* Significant at 5%

** Significant at 1%

The pooled data indicated no significant effect on days taken to bud sprout under canopy modifications. However, year-wise observation for days taken to bud sprout showed early spouting in SCH except in year 2012–2013. Early spouting in SCH could be considered as the effect of vertically positioned shoots on this cordon arrangement that has resulted into uniform sunlight on each bud to sprout.

The shoot length was highest in DCH (105.32 cm) and found decreased in SCH (96.08 cm) followed by FCH (81.99 cm). Though the variation in cane diameter was non-significant, highest diameter was recorded in DCH (9.19 mm). Total number of canes per vine significantly increased during all the years of study. The highest total numbers of cane/vine were recorded in FCH (69.00) while lowest in SCH (36.16). The considerable vegetative growth induced by canopy modification might be due to consolidation of food material in growing parts supported by photosynthetically active leaves. The increasing total number of canes per vine from SCH to FCH was evidenced as direct influence of increasing number of cordons from SCH to FCH as result of canopy modification. The increased cane number under each modification from SCH to FCH might have reduced the shoot length.

The canopy modifications had marked influence on photosynthesis rate, stomatal conductance, and transpiration rate. The highest LAI was observed in DCH in comparison with SCH and DCH and found in increasing order across all the years. Whereas, FCH showed least values of LAI and found increasing as year progresses from 2010–2011 to 2013–2014. From pooled data, the highest LAI (1.89) was recorded in DCH (Table 1). Hunter et al. (1995) concluded that an additional compensatory growth and energy demand brought about by lateral removal could have a direct impact on metabolic processes in the grapevine, particularly, availability and distribution of carbohydrates for bunch development.

Year-wise data for photosynthesis rate was in increasing order for all the three canopy modification systems studied. The canopy modification under DCH was photosynthetically active compared to SCH and FCH. The pooled data reported in Table 1 indicated highest photosynthesis rate in DCH (13.78 µmol.cm⁻² s⁻¹) while least in FCH (9.36 µmol.cm⁻² s⁻¹). For canopy modification treatments SCH and DCH, the stomatal conductance was observed in increasing order from year 2010–2011 to 2013–2014 (SCH 0.16–0.21 cm·s⁻¹; DCH 0.20–0.29 cm·s⁻¹). Among the different canopy modifications, stomatal conductance was highest in DCH (0.25 cm·s⁻¹) while least in FCH (0.12 cm·s⁻¹). The vines trained to DCH recorded highest transpiration rate (3.01 µmol.H₂O m⁻² s⁻¹) while it was least in FCH (1.60 µmol.H₂O m⁻² s⁻¹). Among the different canopy modifications, highest transpiration rate was found in DCH while least in FCH during all the years of study. Previous studies demonstrated that change in canopy microclimate increases photosynthetic activity and export of photo assimilates (Hunter and Visser, 1988b; Koblet, 1975; Somkuwar et al., 2014).

Effect of Canopy Modifications on Yield and Yield Components

Significant differences were recorded for yield and berry quality under different canopy modifications. Total number of bunches/vine varied significantly from SCH to FCH in all the years. The highest number of bunches were recorded in FCH (65.36 bunch/vine) followed by DCH (50.23 bunch/vine) and SCH (47.24 bunch/vine). Across the years, average bunch weight increased in all the canopy modification treatments. From pooled data, SCH performed better for average bunch weight (259.04 g) than DCH (252.37 g) and FCH (211.13 g). During the initial 2 years (2010–2011 to 2011–2012), 50 berry weight was higher in SCH but during the next 2 years, it was higher in DCH. As per pooled data, it was significantly higher in SCH (140.18) followed by DCH (135.15) and FCH (120.76). The yield per vine was found to be increasing from SCH to FCH in all the 4 years. The highest yield/vine was recorded in FCH (13.91 kg) followed by DCH (13.13 kg) and SCH (11.97 kg). In general, the yield and total number of bunches/vine increased with decrease in average bunch weight and 50 berry weight from SCH to FCH. Smart (1985) and Smart et al. (1990) reported that improved fruit yield and wine quality in case of vigorous and robust growing varieties with dense canopies can be achieved by optimizing sunlight interception, photosynthetic capacity, and fruit microclimate through canopy management practices such as different methods of trellis system, training systems, pruning methods, and use of rootstocks. Liu et al. (2015) and Reynolds and Wardle (1993) reported the increased vine yield with consistent effect on training system. In grapes, change in microclimate due to variations in canopy affects the berry development. Gonzalez-Neves et al. (2004) reported the change in anthocyanin profile of the grapes depended on yields and environmental conditions. The shoot position on cordon that helps to receive uniform sunlight on each bud makes it more fruitful. Generally, sunlight penetration and yield are positively correlated because increased shoot exposure improves bud fruitfulness (Cartechini and Palliotti, 1995; Perez and Kliewer, 1990; Shaulis et al., 1966; Smart et al., 1982).

From the pooled data, it was observed that highest berry diameter was noted in DCH (16.28 mm) whereas it was least in FCH (15.06 mm). Among the different modifications, berry diameter was found to be consistently higher in DCH throughout the years. Somkuwar et al. (2014) reported a variation in berry quality parameters due to the canopy manipulation practices. They found that increased berry diameter was witnessed in shoot thinning with leaf removal. However, berry growth after flowering was highly dependent on supply of photo assimilates (Keller, 2009). From pooled data, significant difference was noticed in berry length. The highest berry length was noticed in DCH (19.13 mm) followed by SCH (18.11 mm) and FCH (17.16 mm) canopy modifications treatments (Table 2). Though the effect of canopy modification was distinguished by lower berry length in FCH, canopy management practices like leaf removal improved the bunch and berry characteristics in Graciano and Carignan grapes (Tardaguila et al., 2010).

Table 2. Effect of canopy modification on yield and yield components on Tas-A-Ganesh grapes.

	Total number of bunches/vine					Yield per vine (kg)					Average bunch weight (g)
Treatments	2010–11	2011–12	2012–13	2013–14	Pooled	2010–11	2011–12	2012–13	2013–14	Pooled	2010–11	2011–12	2012–13	2013–14	Pooled
SCH	44.62	47.01	41.82	55.50	47.24	8.70	12.04	11.32	15.83	11.97	215.94	264.20	270.70	285.30	259.04
DCH	46.15	48.31	48.17	58.30	50.23	9.64	12.42	13.57	16.91	13.13	188.50	249.27	281.71	290.00	252.37
FCH	58.81	64.06	69.36	69.20	65.36	10.26	12.80	14.58	17.99	13.91	174.48	199.78	210.26	260.00	211.13
CV %	3.52	2.74	2.72	3.08	6.17	1.50	2.59	1.99	1.73	4.25	3.31	2.84	2.51	2.51	6.01
LSD 5%	1.9	1.49	1.45	9.90	5.80	0.16	0.34	0.24	0.32	0.96	7.45	6.53	6.54	8.12	25.05
Significance	**	**	**	*	**	*	**	**	**	**	**	**	**	**	**
	Fifty berry weight (g)					Berry diameter (mm)					Berry length (mm)
Treatments	2010–11	2011–12	2012–13	2013–14	Pooled	2010–11	2011–12	2012–13	2013–14	Pooled	2010–11	2011–12	2012–13	2013–14	Pooled
SCH	135.00	145.00	138.12	142.60	140.18	13.11	16.18	15.24	17.20	15.43	17.90	17.40	18.95	18.20	18.11
DCH	115.00	141.00	139.31	145.30	135.15	14.57	16.90	16.35	17.30	16.28	18.60	18.00	20.07	19.86	19.13
FCH	103.00	129.35	118.10	132.60	120.76	13.06	14.96	15.05	17.15	15.06	16.30	16.95	17.80	17.60	17.16
CV %	3.53	2.93	2.89	2.89	4.54	1.98	2.59	2.48	2.48	3.00	2.29	2.43	2.29	2.29	2.12
LSD 5%	7.45	4.32	4.37	4.02	10.38	0.31	0.44	0.43	0.48	0.81	0.50	0.50	0.46	0.58	0.67
Significance	**	**	**	**	**	*	*	**	NS	**	**	*	**	**	*
	Total soluble solid (°Brix)					Total acidity (%)
Treatments	2010–11	2011–12	2012–13	2013–14	Pooled	2010–11	2011–12	2012–13	2013–14	Pooled
SCH	22.70	20.80	22.10	22.20	21.95	0.49	0.60	0.55	0.59	0.56
DCH	21.10	19.80	22.05	22.10	21.26	0.53	0.66	0.52	0.55	0.57
FCH	20.00	19.50	20.00	21.60	20.28	0.57	0.65	0.58	0.63	0.61
CV %	2.90	2.23	2.39	2.39	2.87	3.50	2.72	2.50	2.79	6.00
LSD 5%	0.71	0.52	0.55	0.62	1.05	0.02	0.02	0.01	0.02	0.06
Significance	**	**	**	*	*	**	*	**	**	*

* Significant at 5%

** Significant at 1%

Influence of Canopy Modification on Fruit Parameters

Canopy modification changed the TSS significantly from SCH to FCH and same trend was observed for all the years of study (2010–2011 to 2013–2014). From the pooled data, total acidity increased with the increase in number of cordons (SCH to FCH). Among the different training modifications, the lowest total acidity was recorded in SCH (0.56%). We observed that as bunch load increased, TSS was decreased while the total acidity increased (Table 2). The deterioration in quality might be due to increase in yield and consequent dilution of sugars in berries. The results of the present study are in conformity with the results obtained by Singhrot et al. (1977) in Thompson Seedless. Decreasing TSS from SCH to FCH explains the importance of open canopy for maximum entrapment of sunlight (Satisha et al., 2013). Smart et al. (1988) and Macaulay and Morris (1993) also observed higher TA in shaded treatments. Sunlight-exposed fruits in open canopy are generally rich in total soluble solids and reduced titratable acidity than that of fruits in non-exposed or dense canopy (shaded) (Ferree et al., 2004; Kliewer and Dokoozlian, 2005; Main and Morris, 2004; Santesteban and Royo, 2006).

Disease Assessment

The disease assessment data from different canopy modifications (Table 3) revealed that powdery mildew incidence was significantly increased from SCH to FCH. The lowest disease incidence was observed in SCH (19.00%), whereas highest disease incidence was observed in FCH (32.75%). The phenolic content estimated in different canopy modifications revealed that the phenolic content was decreased with the increase in number of cordons. In the present investigation, the increase in number of cordons increased the canopy. The reduction in phenolic content was correlated with increase in powdery mildew incidence. Comparatively, among the years, highest content of phenolics was noted in the year 2013–2014. The increase in canopy provides an ideal microclimate for the development of diseases. Patil et al. (2012) reported that highly dense vines have higher incidence of powdery mildew (38.38%) and downy mildew (21.37%). Similar results were also reported by Reynolds et al. (1994) in Riesling grapes, Freeman et al. (1979) in Shiraz vines, and Cheema et al. (2003) in Perlette grapes.

Table 3. Effect of canopy modification on disease incidence and total phenolic content in Tas-A-Ganesh grapes.

	PDI for powdery mildew					Total phenolics (mg/g)
Treatments	2010–11	2011–12	2012–13	2013–14	Pooled	2010–11	2011–12	2012–13	2013–14	Pooled
SCH	20.00	29.00	17.00	10.00	19.00	0.93	0.86	0.98	1.12	0.93
DCH	37.00	40.00	21.00	17.00	28.75	0.88	0.81	0.92	0.98	0.88
FCH	51.00	32.00	30.00	18.00	32.75	0.78	0.70	0.88	0.93	0.78
CV %	3.59	2.07	0.86	1.90	25.15	3.37	3.37	3.00	3.36	3.06
LSD 5%	1.50	1.19	0.20	0.33	11.68	1.50	0.03	0.03	0.03	0.05
Significance	**	**	**	**	*	**	**	**	**	**

* Significant at 5%

** Significant at 1%

The correlations between different parameters studied were reported in Table 4. The vegetative character such as shoot length was found positively correlated with yield related parameters (average bunch weight, 50 berry weight, and berry diameter) and photosynthetic parameters (LAI, Photosynthesis rate, stomatal conductance, and transpiration rate). Average bunch weight showed positive correlation with yield per vine, 50 berry weight, berry diameter, berry length, TSS, LAI, Stomatal conductance, Transpiration rate, and phenolics and negatively correlated with percent disease index (PDI) for powdery mildew. Further, it was found that photosynthetic parameters LAI showed positive correlation with photosynthesis, stomatal conductance, and transpiration rate. The TSS was negatively correlated with total acidity and PDI for powdery mildew and positively correlated with total phenolics. Very strong negative correlation was evidenced between PDI for powdery mildew and total phenolics.

Table 4. Correlation coefficient between different parameters influenced by canopy modificationsinTas-A-Ganesh grapes.

	April pruning weight	Shoot length	Cane diameter	Total number of canes per vine	Total number of bunches per vine	Average bunch weight	Yield per vine	Fifty berry weight	Berry diameter	Berry length	Total soluble solid	Total acidity	Leaf area index	Photosynthesis rate	Stomatal conductance	Transpiration rate	PDI for powdery mildew	Total phenolics
April pruning weight	1	0.488	0.075	0.463	0.271	0.382	0.524	0.368	0.601*	0.342	−0.259	0.482	0.537	0.362	0.441	0.485	0.008	−0.246
Shoot length		1	0.185	−0.155	−0.169	0.672*	0.438	0.767**	0.759**	0.437	0.233	0.276	0.706*	0.729**	0.728**	0.747**	−0.376	0.326
Cane diameter			1	−0.555	−0.599*	0.060	−0.441	0.312	−0.114	0.397	0.194	−0.326	0.077	0.479	0.469	0.486	−0.060	0.010
Total number of canes per vine				1	0.926**	−0.177	0.611*	−0.320	0.220	−0.280	−0.526	0.565	0.102	−0.398	−0.371	−0.362	0.158	−0.363
Total number of bunches per vine					1	−0.185	0.649*	−0.318	0.168	−0.369	−0.403	0.480	0.129	−0.481	−0.469	−0.490	0.050	−0.190
Average bunch weight						1	0.603*	0.877**	0.818**	0.656*	0.584*	0.016	0.653*	0.541	0.711**	0.672*	−0.762**	0.679*
Yield per vine							1	0.383	0.813**	0.255	0.123	0.407	0.677*	0.130	0.225	0.197	−0.514	0.386
Fifty berry weight								1	0.695*	0.518	0.484	0.101	0.540	0.504	0.659*	0.634*	−0.702*	0.468
Berry diameter									1	0.460	0.165	0.442	0.733**	0.517	0.585*	0.631*	−0.500	0.424
Berry length										1	0.644*	−0.488	0.695*	0.803**	0.892**	0.817**	−0.566	0.557
Total soluble solid											1	−0.683*	0.450	0.402	0.494	0.352	−0.789**	0.811**
Total acidity												1	0.451	−0.122	−0.031	−0.086	−0.263	0.161
Leaf area index													1	0.715**	0.730**	0.674*	−0.490	0.452
Photosynthesis rate														1	0.954**	0.960**	−0.245	0.398
Stomatal conductance															1	0.972**	−0.419	0.465
Transpiration rate																1	−0.301	0.384
PDI for powdery mildew																	1	−0.807**
Total phenolics																		1

* Correlation is significant at the 0.05 level (two-tailed); ** Correlation is significant at the 0.01 level (two-tailed).

Among the three types of canopy modifications studied, it was concluded that vines with SCH modification performed consistently better for low incidence of powdery mildew and for vegetative growth, improving production potential as compared to DCH and FCH. However, considering the incidence of powdery mildew, growth, yield, and berry quality, the vines trained to double cordon placed horizontally (DCH) seems to be an ideal one.