Yield and Physiological Response of Autumn King and Scarlet Royal Table Grapes to Cane and Spur Pruning Systems

Abstract

The type of training system affects vine growth and productivity; however, there is a lack of knowledge on the suitability of pruning systems for some recently introduced (Vitis vinifera L.) cultivars. In this study, we provide the growers with science-based information about the response of two table grape variates to cane and spur-pruning systems to develop the best cultural practices. In 2013, a vineyard was established at Kearney Agriculture Research Center, Parlier, California using “Autumn King” and “Scarlet Royal” table grapes (Vitis vinifera L.) grafted on Freedom rootstock. The performance of the three-year-old vines was assessed under two pruning systems, Quadrilateral cordon training (spur-pruning) and Head training (cane pruning). Data from the 2016 and 2017 seasons showed no significant differences in leaf area, chlorophyll content, Normalized Difference Vegetation Index (NDVI), and pruning weight between the two pruning systems in both cultivars. In both seasons, marketable yield did not vary between the two pruning systems in the Scarlet Royal. However, Autumn King marketable yield was significantly reduced when using the Quadrilateral cordon training (spur-pruning). Petioles nutrient analysis at bloom showed a non-significant increase in nitrate content in the cane pruned vines of both varieties. No significant difference was observed in cluster weight, berry physical, or chemical composition. It seems that both training systems could be used for Scarlet Royal. However, the cane pruning system in Autumn King produced higher yield without affecting cluster and berry quality. The different responses of the two varieties could be due to the genetic background and growth behavior. Our data confirmed the notion that the different responses to the training methods by various grape varieties may involve the genetic background, growth behavior, as well as nutrient uptake and usage by the vines. Establishing the proper training system for each grape variety is essential.

1. Introduction

While the primary reason for grapevine training is to keep fruit off the ground and to facilitate cultural operations and harvest, a proper training system is crucial to maintain vineyard productivity. Training starts in the early years of the vineyard by manipulating vine architecture. There is a lack of knowledge on the suitability of pruning systems for some recently developed (Vitis vinifera L.) cultivars. Autumn King is a white seedless late season maturing table grape variety. This cultivar, formerly known as C10, was released in 2006 and resulted from the cross of USDA selections 61–20 x B99-131 [1]. Scarlet Royal is a red seedless mid-season maturing variety that has large, sweet, and firm berries with a neutral flavor. These cultivars were developed by David Ramming and Ronald Tarailo of the USDA-ARS in Fresno, California and exclusively licensed to California Table Grape Commission. Quadrilateral cordons and spur-pruning were suggested for Scarlet Royal [2]. However, the growers in the San Joaquin Valley of California follow both cane and spur-pruning. Thus, both methods need to be evaluated to provide the growers with a clear answer about the advantages and disadvantages of each method. During vineyard establishment, either cane or spur-pruning has been followed yearly to maintain vine productivity. Cane pruning involves cutting the one-year-old shoot to contain 8–14 buds, whereas this length is usually limited to two buds in spur-pruning. The type of training system affects vine growth and productivity through several variables such as bud fertility, number of inflorescence primordia, cluster exposure, vine water status, and leaf transpiration [3,4]. Choosing the appropriate method for pruning depends on the bud fertility of the cultivar and its vigor. Unlike cane pruning, spur pruning does not require professional labor and is less expensive. In some varieties such as Vidal Blanc, vines were more productive in cordon-trained systems compared to those on head-pruned systems. The cordon-trained vines were easy to train and produced larger crops than the head-trained vines, and this training system reduced crop loss due to the winter damage [5]. This increase in productivity could be due to the use of older wood as well as the spread of the spurs along the cordon on the larger area, which allows better exposure of the shoots and fruits to sunlight [5]. In Cabernet Sauvignon, cordon-trained vines had greater bud burst and were easy to prune as well as harvest compared to the cane-pruned vines. This could be due to a large amount of permanent wood which acts as a reservoir for carbohydrates. In the cane pruned vines, the basal half of the canes exhibited more blind buds and the growth patterns variability reduced as cane length decreased [6]. Spur-pruning of Cabernet Sauvignon vines resulted in higher shoot growth and pruning weight [7]. Moreover, a higher bud break percentage was noticed compared to cane pruning. However, cluster and berry quality did not vary significantly between the two pruning systems. It is unlikely that the increase in yield by spur-pruning could be linked to an increase in bud initiation. In this regard, it was reported that pruning systems did not affect the inflorescence number per shoot and, consequently the fruitfulness of Sauvignon Blanc grapevines [8]. Further, the type of pruning did not affect the inflorescence architecture or distribution. However, in some cordon-trained varieties, spurs disappeared due to the exposure of the pruning cuts to different biotic and abiotic stresses. This could be cultivar dependent and might result in a smaller number of clusters and, consequently a smaller crop. For example, Ugni Blanc showed significantly more necrosis than either Cabernet Sauvignon or Sauvignon Blanc grape after 8 months of the pruning [9]. The loss of fruitful spur positions from the main cordons would affect long-term vine structure, productivity, and vineyard sustainability. Pruning system affects the susceptibility of the vines to the grapevine trunk diseases (GTD) that can affect bud burst and yield. Shorter pruning is associated with higher incidence GTD compared to longer pruning [9].

However, spur-pruning can be used to reduce bud death in some varieties. For example, training of Cabernet Sauvignon grapevine on cordons with 2-node spurs was the most effective pruning system and reduced bud death [4]. However, training the Sultana grapevines on a 6-node cordon reduced the pruning time by 75% and did not affect the yield [10]. Further, vine productivity was similar in cane and spur-pruned Cabernet Sauvignon grapevines [11].

On the other hand, the higher yield of the Concord and Niagara cane pruned grapevines led to overcropped and reduced vine size, while spur-pruning resulted in a balance between the vine crop and size [12]. In table grapes, it is known that leaving many buds on the vines produces several clusters, resulting in reduced cluster and berry quality. Among cultivars, berry compositions respond differently to the pruning type and severity. In this concern, it was reported that soluble solids, acidity, and pH were reduced slightly by using the high cordon pruning system; however, the differences were small and acceptable in Vidal blanc grapes [5]. In Chambourcin grapes, pruning severity effects on berry composition varies from year to year. It was found that Total Soluble Solids (T.S.S.) increased linearly with an increase in pruning severity [13]. Maintaining an optimum balanced canopy size through the pruning system is required to obtain better yield and fruit quality in grapes. Variety-specific standardization of pruning is crucial to sustaining its productivity and fruit quality [14]. The above-mentioned authors reported that pruning most of the canes to short spurs led to the loss of reserved nutriments and reduced vine vigor.

Additionally, the training system can affect the susceptibility of the grapevine to some environmental stressors, such as drought, by affecting the vine water status [15]. The training system also affects sunlight interception and, consequently, bud initiation, development, as well as bud burst. Modifying the training system might be required to optimize the canopy size and yield [16]. Further, the training system and the gaps among shoots could play a role in vine susceptibility to some diseases, such as Botrytis, that can cause bunch rot [17]. Using a training system that allows spacing among canes increases vine yield and fruit quality [18]. The canopy physiology assessment of pruning systems has relied on the estimation of leaf layer numbers and percent of sun-exposed and shaded leaves and determined by measuring the photosynthetic photon flux density [4]. Indeed, the training system change the amount of light that reaches the basal buds of the trellis [19]. However, the implications for crop management by these approaches are truly beyond this complexity and importance. For example, expected growth compensation from a sparsely populated, the sprawling canopy would cause a seasonal and dynamic variation in leaf area production, canopy age, and source-sink balance. Inflorescence primordia formation which is contributed to overall yield is influenced by several internal and external factors including the vine nutrient status, carbohydrate and other environmental factors [20,21]. Pruning system change the architecture of the vine and its performance and probably the inflorescence primordia formation. However, the genetic background contributes to the response of a specific variety to these external factors and internal factors [21].

Thus, in this study, we attempted to assess the performance of two recently developed cultivars, “Autumn King” and “Scarlet Royal” table grape, under cane and spur-pruning systems to develop the best cultural practices for the growers.

2. Materials and Methods

2.1. Site Establishment and Pruning Systems

In 2013, a table grape vineyard was established at the University of California Kearney Agriculture Research and Extension Center, Parlier, CA using vines of Autumn King and Scarlet Royal grafted on Freedom rootstock. Vines were planted at 2.44 × 3.66-m, row orientation was South-North, and an open gable trellis system was used to support the vines. Two pruning systems were used to train the vines, Quadrilateral cordon training (spur-pruning) and Head training (cane pruning), the two systems represent the two major training systems used in the Californian table grape vineyards. In this study, measurements and data were collected in 2016 and 2017. In the spur pruned vines, 7–8 spurs (2 buds’ length) were left on each cordon during the winter pruning. In the cane pruned vines, we left four canes on each vine with 12–15 buds with a total of 60 buds per vine. The two pruning methods were previously described [22]. During the summer, similar to industrial practices, clusters were thinned to have a reasonable space between clusters by removing the crowded and misshaped clusters. This operation allowed the clusters to grow without touching each other.

The advantage of this experimental site was that all the vines under study were located near each other in one quart of a hectare and with no restrictions for applying the appropriate experimental design, for the type of pruning to be distributed within the research plot. The experimental design was a randomized complete block with two pruning methods and four replications using 18 vines per replicate, with a total of 72 vines per cultivar per pruning system. All cultural practices were conducted according to University of California Cooperative Extension (UCCE) guidelines. Local weather conditions during the two seasons are included in

Table 1. Monthly average of different weather conditions of the experimental site (Parlier, CA, USA). Data obtained from CIMIS (https://cimis.water.ca.gov/ (accessed on 21 January 2022)).

Year-Month	Avg Sol Rad (W/sq.m)	Avg Vap Pres (kPa)	Avg Max Air Temp (C)	Avg Min Air Temp (C)	Avg Air Temp (C)	Avg Max Rel Hum (%)	Avg Min Rel Hum (%)	Avg Rel Hum (%)	Avg Dew Point (C)	Avg Wind Speed (m/s)	Avg Soil Temp (C)
16-Jan.	69	1	14.4	5.1	9.3	96	65	85	6.9	1.4	10.1
16-Feb.	153	1.1	20.1	4.9	11.9	96	47	75	7.6	1.2	12.8
16-Mar.	192	1.2	20.7	7.7	14.2	94	45	71	8.8	1.8	16.1
16-Apr.	254	1.2	25.2	10.4	17.5	89	31	58	8.8	1.9	19.6
16-May	302	1.2	28.6	13.4	21.2	85	27	50	9.9	1.8	22.9
16-Jun.	333	1.3	34.9	16.1	25.8	75	17	38	10.5	1.8	25.4
16-Jul.	336	1.4	36.7	17	27.4	77	17	38	11.7	1.7	26.4
16-Aug.	298	1.4	35.9	16.1	26.1	83	18	42	11.9	1.4	26
16-Sep.	245	1.2	32.3	12.9	22.3	82	20	45	9.7	1.3	23.1
16-Oct.	165	1.2	25.8	9.7	17.4	88	33	60	9.5	1.3	19.1
16-Nov.	106	1.1	20.8	5.8	12.5	95	46	76	8.2	1	15.5
16-Dec.	75	0.9	13.7	3	7.8	96	63	85	5.4	1.2	10.8
17-Jan.	72	1	13.3	4.3	8.7	95	65	84	6.1	1.4	10.2
17-Feb.	109	1.1	16.8	7.3	11.8	94	59	78	8.1	1.6	12.7
17-Mar.	194	1.1	21.4	7.1	14	94	41	69	8.2	1.6	15
17-Apr.	240	1.1	23.4	9.1	16.1	90	31	58	7.7	2.3	17.2
17-May	295	1.2	28.3	13	20.9	82	27	48	9.4	2.1	21.6
17-Jun.	319	1.5	34	17.2	26	77	22	43	12.1	2.1	24.4
17-Jul.	274	1.5	37.3	18.6	28.1	77	19	40	13.2	1.8	27
17-Aug.	227	1.7	36.2	19.1	27.6	80	24	45	14.6	1.7	27.9
17-Sep.	214	1.5	31.4	15	23	83	26	50	12	1.7	24.9
17-Oct.	174	1	26.4	7.9	16.4	87	26	55	7.2	1.3	19.7
17-Nov.	108	1.1	20.4	6.7	12.9	91	45	73	7.7	1.4	16.1
17-Dec.	95	0.7	16.4	0.1	7.1	91	38	67	1.4	1.1	9.9

and

Table 2. Total monthly of precipitation (Precip) and evapotranspiration (Eto) of the experimental site (Parlier, CA, USA) during 2016 and 2017 seasons. Data obtained from CIMIS (https://cimis.water.ca.gov/ (accessed on 21 January 2022)).

2016
Month	Jan.	Feb.	Mar.	Apr.	May	June	July	Aug.	Sept.	Oct.	Nov.	Dec.
Total ETo (mm)	24.09	61.88	93.46	137.94	180.52	213.47	222.52	193.92	144.1	87.45	45.17	24.42
Total Precip (mm)	87.5	3.2	57.9	18	14.9	0.1	0.2	0	0	20.9	11.7	64
2017
Month	Jan.	Feb.	Mar.	Apr.	May	June	July	Aug.	Sept.	Oct.	Nov.	Dec.
Total ETo (mm)	24.69	39.25	94.22	130.22	179.1	204.93	201.25	165.42	132.75	94.67	49.06	39.36
Total Precip (mm)	122.3	58	32.2	26.9	3.8	0	0	0.2	5.2	1.7	9.3	1.2

.

2.2. Vine Vigor, Canopy Development, and Photosynthetic Activity

In both variates, different parameters were used to measure vine vigor and canopy development under the two pruning systems. For example, leaf area was measured using Li-Cor 3000, LI-COR Biosciences, USA, using 15 leaves from each replicate. Further, the SPAD-502 leaf-clip chlorophyll meter (Konica Minolta, Inc., Tokyo, Japan) was used to measure the relative chlorophyll content in 10 leaves from each replicate at mid-day at bloom stage. The measurement area of the meter was 6 mm² and the output is in SPAD units which were used as an indicator of the total chlorophyll content. Moreover, the Normalized Difference Vegetation Index (NDVI) was performed on 10 leaves from each replicate, using FieldScout CM 1000 NDVI meter (Spectrum Technologies, Inc., Aurora, IL, USA) as an indicator for photosynthetic activity. All leaf measurements were carried out on the leaves facing the clusters on the shoots. During winter, the main trunk diameter was measured 30 cm below the vine head using flexible measuring tape. Additionally, the pruning wood weight for each individual vine was recorded as an indicator of vine growth during the season. Moreover, 50 petioles were collected at bloom from each replicate (18 vine) and sent to a plant laboratory to be analyzed for macro and micronutrients as well as salts. During winter pruning, the weight of the removed wood from each vine was determined in the field immediately after pruning, values were used as indicator for the whole season canopy growth. Pruning was performed on mid-January from each year.

2.3. Petiole Nutrient Analysis

At bloom, fifty leaves from each replicate (18 vines) with a total of 200 leaves from each treatment were collected for nutrient analysis. We selected the leaf at the front of the cluster and immediately separated the petiole from the blade. Petioles were transported to the laboratory, triple washed with distilled water, and sent to a private laboratory for analysis. Nutrients content was determined using the methods described in [23].

2.4. Yield and Berry Compositional Analysis

At harvest of 2016 and 2017, clusters were hand-picked, cleaned by removing the undesirable and damaged berries from the clusters and the wight of these clusters was taken as a total marketable yield. Harvest time was decided based on the industry standard berry sugar level, random berry samples were collected and measured in the field by handheld refractometer, Scarlet Royal variety was harvest when the random brix was 21 and 17 for the Autumn king. Further, random samples of 50 berries per replicate were collected to measure the berry weight, length, diameter, and firmness using the Firm Tech2 instrument, PA, USA. These berries were then macerated in an electric blender, filtered through a Whatman #1 filter, and an aliquot of juice was used to determine soluble solids (ᵒBrix), pH, and titratable acidity (TA). Soluble solids were determined using a digital hand-held, temperature compensated refractometer, model # RHB-32 (Spectrum Technologies, IL, USA). The TA and pH were determined by titrating a 40 mL aliquot of juice with 0.1 N NaOH to a pH of 8.2 using an automatic titrator Excellence T5 (Mettler-Toledo, OH, USA). The machine was calibrated using potassium Hydrogen phthalate according to the manufacturer recommendation. Harvest of the Scarlet Royal was performed in the middle of August and in the middle of October for the Autumn King during both years of study.

2.5. Experimental Design and Statistical Analysis

For both variates, there were two pruning methods with four replications. Pruning methods were in a randomized complete blocks design for both seasons. After passing the normality test, two sets of statistical analyses were performed using SigmaStat (Systat, CA, USA). To determine the difference between the two pruning systems within the same variety, two ways ANOVA was performed. The significant difference between treatments was evaluated using Tukey’s Honestly Significant Difference (HSD) multiple comparison test (p ≤ 0.05) within the same variety and year. To determine the effect of the variety, year, pruning system, and their interactions, three ways ANOVA statistical analyses were performed using the Holm-Sidak multiple comparisons test.

3. Results

3.1. Vine Vigor, Canopy Development, and Photosynthetic Activity

Leaf area data showed no significant difference between the two pruning systems in both varieties, data also showed no effect of the year on the leaf area. However, a significant difference was observed between the two varieties during the two years of study. It seems that Autumn king possesses larger leaves compared to Scarlet Royal. For example, the Scarlet Royal average leaf area values were 98.9 and 104.7 cm² for cane and spur-pruning respectively in 2016, and 94.7 and 99.7 cm² in 2017. On the other hand, the Autumn King leaf area values in 2016 were 128.7 and 122.0 cm², and in 2017 they were 122 and 127 cm² in the cane and spur pruned vines, respectively (Figure 1A).

Leaf chlorophyll content as presented in the SPAD index showed no significant difference between the two pruning systems in both varieties (Figure 1). Further, in Scarlet Royal table grape, no significant changes were observed from year one to year two of the study, however, in Autumn King, slightly higher significant SPAD values were observed in the second season regardless of the pruning system. For example, SPAD values for Scarlet Royal were 53.4 and 50.9 units in 2016, and 52.3 and 52.4 units in 2017 for cane and spur-pruning, respectively. In Autumn King, the SPAD index values were 50.1 and 47.3 units in 2016, and 52.5 and 52.4 units in 2017 for the cane and spur-pruned vines, respectively (Figure 1B).

NDVI data showed an overall significant difference between the two pruning systems and the two years of study. Interestingly in 2016, the NDVI showed a significant difference in Scarlet Royal between the two pruning systems (Figure 1C). However, no significant difference was observed between the cane and spur-pruning systems in 2017. To elaborate, in 2016, NDVI values were 0.95 and 0.92 units for the cane and spur-pruning, respectively. However, in 2017, these values were 0.98 units for cane pruning and 0.98 units for spur-pruning (Figure 1C). In Autumn King, although in 2016 NDVI data showed a significant decrease in photosynthetic activity in the spur-pruned vines compared to the cane-pruned ones, this significant reduction was not observed in 2017. In 2016, NDVI values were 0.95 and 0.91 units, whereas in 2017, values were 0.98 for both cane and spur-pruned vines (Figure 1C). Variation in the NDVI from year one to year two could be related to the differences in the climate. A significant interaction was observed between the effect of the year and the pruning system.

Winter pruning weight as an indicator for the season canopy growth did not show any significant response to the pruning systems or to the variety, however, a significant difference was observed between the two years of the study (Figure 1D). For example, in Scarlet Royal, in 2016, the pruning wood weight was 5.9 and 5.4 kg/vine for cane and spur-pruning, respectively. While in 2017 these values reached 9.2 and 8.4 kg/vine. Similarly, data presented in Figure 1D showed that in 2016, Autumn King pruning weight was 5.6 and 5.7 kg/vine for cane and spur-pruning, respectively. However, in 2017, these values were 11.3 kg/vine for the cane pruned vines and 11.5 kg/vine for those that were spur-pruned.

Generally, trunk circumference measurements showed a significant difference between the two years of the study and varieties; however, the pruning methods showed only significant difference in the 2017 season in the Scarlet Royal (Figure 2A). In 2016, Scarlet Royal cane and spur-pruned vines did not show a significant difference in the trunk circumference. However, in 2017, the trunk circumference of the cane pruned vines were 161.2 mm compared to 150.3 mm in the spur-pruned vines (Figure 2A).

In both seasons, Autumn King cane and spur-pruned vines did not show a significant difference in the trunk circumference (Figure 2A). In 2016, Autumn King trunk circumference values were 152.9 and 147.0 mm for the cane and spur-pruned vines. However, in 2017, these values were 222.9 mm in the cane pruned vines and 252.8 mm in the spur-pruned ones (Figure 2A). The increase in trunk circumference over the two seasons is a natural result of overall vine growth and development. A significant interaction was observed between the effect of the year and the variety on the trunk circumference.

3.2. Bud Fruitfulness, Yield, and Berry Composition Analysis

To investigate the effect of the two pruning systems on Scarlet Royal bud fruitfulness, the cluster numbers were counted in early spring of both seasons.

Statistical analyses showed an overall significant effect of the year, pruning system, and variety on the cluster number per vine. In 2016, the Scarlet Royal cluster number was significantly lower in the spur-pruning vines (22.0) compared to the cane pruning system (35.3) (Figure 2B). Although the same trend was observed in 2017, the difference in cluster numbers between the two pruning systems was not statistically significant. When comparing the two systems, a significant reduction in Autumn King cluster numbers was observed with the usage of the spur-pruning system. The cluster numbers on the spur-pruned vines were 17.3 and 20.8 compared to 31.3 and 41.6 on the cane-pruned vines in 2016 and 2017, respectively (Figure 2B). Conforming the above-mentioned results, statistical analysis showed a significant effect of the pruning system, year, variety and interaction between year and variety on cluster number. Average cluster weight was not affected by the year or the pruning system; however, it was affected by the variety. In general, the cluster weight of Scarlet Royal showed a lower value compared to that of the Autumn King. Data presented in Figure 2C reveals that in 2016, the cluster weight values of the Scarlet Royal were 394 and 426.6 g, and 359.5 and 428.2 in 2017 in cane and spur-pruning, respectively. During the 2016 season, the Autumn King cluster weight was 508.6 and 563.0 g, and in 2017 it was 403.1 and 520.4 g for the cane and spur-pruned vines, respectively (Figure 2C).

Interestingly in both seasons, the marketable yield of the Scarlet Royal followed the same trend observed in the cluster number. Thus, in 2016, Scarlet Royal’s marketable yield was significantly higher (13.8 kg/vine) in the cane-pruned vines compared to (9.3 kg/vine) in the spur-pruned vines (Figure 2D). However, in 2017, no significant difference in the marketable yield was observed between the cane and spur-pruned vines. In Autumn King, during the 2016 season, the marketable yield decreased from 15.7 kg/vine in the cane-pruned vines to 9.4 kg/vine in the spur-pruned vines. Further, in 2017 the marketable yield of the cane-pruned vines was 16.8 kg/vine compared to 10.7 kg/vine in the spur-pruned vines (Figure 2D). Statistical analyses showed a significant effect of the year and the pruning system on the marketable yield; however, no significant difference was observed between the two varieties. Moreover, a significant interaction was observed between year and variety on marketable yield. Morover, at harvest, we found that the two different pruning systems did not affect the Scarlet Royal or Autumn King berry weight or size; however, a significant difference was observed between the two varieties and the two years of study. In 2016 and 2017, Scarlet Royal berry weight was 5.6 and 7.2 g in the cane-pruned vines compared to 5.4 and 6.8 g in the spur-pruned vines. In Autumn King berries, these values reached 7.9 and 7.5 g in 2016 and 12.5 and 12.4 g in 2017 under cane and spur-pruning, respectively (Figure 3A).

A similar trend was observed in berry length and width (Figure 3B,C). Autumn King tends to have a heavier berry weight compared to Scarlet Royal. Further, berry firmness showed significant response to the year and the varieties under study. For Scarlet Royal, berry firmness values were 311.8 and 314.7 in 2016, and 358.5 and 369.9 in 2017 for cane and spur-pruning, respectively, (Figure 3D) with no significant difference between the two pruning systems. For Autumn King, berry firmness showed a significant increase in spur-pruning only during the 2016 season (Figure 3D). Thus, in 2016, the berry firmness value was 371.5 g/mm in cane pruning compared to 407.3 g/mm in spur pruning. However, in 2017, these values were closer, with no significant difference between the cane (422.4 g/mm) and spur pruning systems (407.6 g/mm) (Figure 3D).

Berry chemical composition analysis indicated that the pruning system did not influence the berry composition including berry sugar content, acidity, pH, and T.S.S./acid ratio (Figure 4). However, statistical analysis showed a significant difference between varieties and years of the study.

For example, in 2016 and 2017, the T.S.S./acid ratio in the Scarlet Royal berries was 56.1 and 28.6 in the cane-pruned vines compared to 58.6 and 29.2 in the spur-pruned vines (Figure 4C). However, T.S.S./acid ratio in the Autumn King berries was 77.1 and 47.4 in the cane-pruned vines compared to 83.0 and 47.9 in the spur-pruned vines in the 2016 and 2017 seasons, respectively (Figure 4C). The difference in the T.S.S./acid ratio between the two varieties could be attributed to the lower acidity level in Autumn King berries compared to Scarlet Royal.

Bloom Petioles Nutrients Content

The effect of the cane and spur-pruning systems on Scarlet Royal petioles’ nutrient content is presented in

Table 3. Scarlet royal and Autumn king petiole’s nutrients content at veraison under cane and spur pruning systems. ANOVA statistical analysis was used to measure the differences among treatments at a 0.05 significance level. Error bars represent the standard deviation. Asterisk (*) indicates the significantly different values.

	Scarlet Royal				Autumn King
	2016		2017		2016		2017
	Cane	Spur	Cane	Spur	Cane	Spur	Cane	Spur
NO3-N (mg/kg)	415.3 *	262.8	2463	2220	386.8	270.0	3606	3518
P (%)	0.17	0.15	0.28	0.25	0.14	0.13	0.35	0.35
K (%)	0.73	0.62	2.28	2.16	0.64	0.57	2.04	1.89
Zn (mg/kg)	35.8	31.8	31.5	24.25	19.0	29.0	33	41.5
Mn (mg/kg)	51.0	51.3	46.8	44.3	47.5	53.8	51.7	49.5
Na (%)	0.018	0.015	0.013	0.010	0.020	0.02	0.013	0.010
B (mg/kg)	34.3	32.3	37.8	37.8	36.8	30.5	41.0	39.5
Ca (%)	1.70	1.58	1.38	1.32	1.58	1.56	1.36 *	1.24
Mg (%)	0.85	0.85	0.32	0.33	0.82	0.85	0.46 *	0.38
Fe (mg/kg)	44.0	43	57.3 *	32.8	45.8	53.8	57.7 *	39.5
Cu (mg/kg)	3.75	4.25	8.00	7.25	6.50	4.5	6.00	5.8
Cl (%)	0.18	0.20	0.10	0.10	0.20	0.20	0.13	0.10

. In both seasons, data showed that the pruning system had no significant effect on Scarlet Royal petioles’ content of nitrogen, phosphorus, potassium, zinc, manganese, sodium, boron, calcium, magnesium, iron, copper and chlorine (Table 3). Data also indicated that, although in 2017 the petioles’ iron content was significantly lower in the spur-pruned vines compared to the cane-pruned vines, no significant difference was observed in 2016 between the two pruning systems (Table 3). A similar trend was observed in Autumn King; data showed that the pruning system had no effect on Autumn King petioles’ content of nitrogen, phosphorus, potassium, zinc, manganese, sodium, boron, copper, and chlorine. Data indicated that, although in 2017, the petioles’ calcium, magnesium and iron content were significantly lower in the spur-pruned vines compared to the cane-pruned vines, no significant difference was observed in 2016 between the two pruning systems (Table 3).

Statistical analysis of nitrogen content showed a significant difference between years and varieties; it seems like Autumn king had a higher nitrogen content compared to the Scarlet Royal regardless of the pruning system. This effect was more evident during 2017 season and that was proven by the significant interaction between years and variety. Phosphorus and potassium content showed a significant difference between the two years of the study, while its content did not change significantly either with the changing the pruning system or variety. These results are aligned with the above-mentioned data on vine vigor and performance during the two years of the study.

4. Discussion

The two varieties used in this study responded differently to the training system. While the marketable yield did not vary significantly in Scarlet Royal, it decreased significantly in the spur-pruned vines of Autumn King during the two years of the study. The reduction in Autumn King yield following spur pruning could be due to the low number of clusters as shown in Figure 2B. It was previously reported that the Autumn King variety is susceptible to powdery mildew [24] which could be a potential factor in losing buds and consequently reducing the cluster numbers. Another explanation is that the larger canopy of Autumn King causes some shading inside the canopy, which may harm the buds and reduce bud break and the number of clusters [25]. Moreover, flower bud initiation and formation are affected by the nutrient’s uptake especially nitrogen and water availability during the previous year [26]. We have observed some changes in the nutrient’s uptake especially nitrogen and that could be corelated with the lower number of clusters. It seems that spur pruning influences the marketable yield by affecting cluster number rather than cluster or berry weight, as they did not vary significantly between the two training systems in both varieties. Similar results regarding the non-significant effect of the training system on berry quality and composition were previously reported [7]; however, others observed changes in berry composition when using different training systems [5,12]. Varieties respond differently to the pruning systems, so establishing a variety-specific standardization of pruning is crucial to sustaining its productivity and fruit quality [13]. The variation in the response of different varieties to the pruning system could be due to the genetic composition of a given variety and its capability to adapt to microclimate conditions such as shading caused by the larger canopy.

Our data confirmed the notion that grape varieties respond differently to the training methods, and this might involve the genetic background, growth behavior, as well as nutrient uptake, and usage by the vines. We observed that both varieties have fruitful basal buds starting from the first bud, so the different response to the pruning system between the two varieties is not attributed to the difference in the basal buds’ fruitfulness. So, establishing the proper training system for each grape variety is essential. Scarlet Royal is a mid-season red variety which is different from Autumn King, a late-season white variety. It seems like Autumn King is more vigorous than Scarlet Royal, which makes this variety respond differently. This is evident from the higher value for leaf area, trunk circumference, and pruning weight. The vigor of Autumn King could be due to its high nitrogen uptake as it shows a superior overall leaf nitrate content compared to Scarlet Royal. These findings coincided with higher values of NDVI in the cane pruned vines in both varieties during the 2016 season indicating a higher photosynthesis capacity for the cane pruned vines compared to those that were spur pruned. These results are in harmony with those previously reported that removing the cane during spur pruning limits vine size and that cane-pruned vines are more vigorous [12]. Our study supports this notion by providing that nitrogen uptake and metabolism could be involved in this process. However, leaf area and SPAD index did not show significant differences between the two training systems in both varieties. Petioles’ nutrient analyses at bloom revealed that the pruning system has no significant effect on the uptake and assimilation of the various nutrients; however, the varieties differ in nitrogen content. Interaction analysis showed a significant effect of the year on several parameters including SPAD, NDVI, Trunk circumference, cluster numbers, berry quality and yield. That could be due to the changes in the weather condition from year to year. For example, early season precipitation from January to May was higher in the 2017 reaching 243.2 mm compared to 210.3 mm in 2016. That could be associated with higher nutrient and water uptake and better vine performance. It seems like the vine behavior, and productivity could vary from year to year. Optimization of the cultural practices for the various grape varieties including the pruning system and the introduction of new varieties could help in the production sustainability especially under expected climate change [27]. However, each variety has its own uptake and assimilation processes that could influence the vine’s productivity and its response to a specific pruning system and microclimate. Despite the fact that we carried the experiment for only two years, our personal observation in various vineyards in California support our finding at advanced age too.

5. Conclusions

Our data collected throughout the two years showed that both Quadrilateral cordon training (spur pruning) and Head training (cane pruning) systems could be used to train Scarlet Royal table grapes. However, Head training (cane pruning) system did show a higher marketable yield in Autumn King compared to Quadrilateral cordon training (spur-pruning). Spur-pruning caused a reduction in cluster numbers and total yield in Autumn King. Cluster and berry quality did not significantly differ between the two training systems. There are significant differences between the two varieties that were reflected in higher levels of petiole nitrogen content, leaf area, and trunk circumference of the Autumn King; however, these morphological differences did not affect the marketable yield. It seems that vine behavior, and productivity could vary from year to year.