Effects of Mepiquat Chloride and Chlormequat Chloride on the Growth and Fruit Quality of ‘Shine Muscat’ Grapevines

Abstract

Excessive shoot vigor in grapevines negatively impacts plant growth and fruit quality, necessitating the use of plant growth regulators (PGRs) for canopy management. This study investigated the effects of mepiquat chloride (MC) and chlormequat chloride (CCC) on shoot growth (including new shoot length, relative chlorophyll content, leaf area, etc.) and fruit quality in Vitis vinifera cv. ‘Shine Muscat’. Different concentrations of MC (100, 300, 500, 700 mg/L) and CCC (100, 300, 500, 700 mg/L) were applied via foliar spraying at multiple stages before flowering. The results demonstrated that both PGRs effectively suppressed shoot elongation, with CCC exhibiting superior inhibitory efficacy compared to MC. However, high concentration of either compound also restricted leaf and cluster development. Optimal treatments MC (500 mg/L) and CCC (100 mg/L) significantly enhanced berry size, soluble solids content (SSC), and solid–acid ratio while maintaining effective shoot control. For practical application, we recommend spraying MC (500 mg/L) or CCC (100 mg/L) during the new shoot growth, flower-cluster separation, and flowering stages of ‘Shine Muscat’ grapevines to improve the new shoot control effect and fruit quality.

1. Introduction

China plays a pivotal role in global viticulture [1]. Grapes (Vitis vinifera L.) represent one of the most economically important fruit crops worldwide, valued for their versatility in fresh consumption, winemaking, and processed products [2]. However, optimal grape production faces significant challenges from excessive vegetative growth caused by factors such as variety, climate, and water–fertilizer management [3].

‘Shine Muscat’ grapevines are particularly sensitive to vegetative overgrowth (excessive shoot and leaf growth) due to their strong growth habit. Vigorous shoot growth in grapevines leads to multiple physiological and agronomic complications. Dense canopies impair photosynthetic efficiency and microclimate conditions, resulting in poor fruit set, reduced berry size, and delayed maturation [4,5]. It also affects flower-bud differentiation and shoot maturation. Furthermore, canopy closure can easily induce pests and diseases, increasing the difficulty of prevention and control [6]. With the expansion of grape cultivation areas and the increase of labor costs, the demand for applying plant growth regulators (PGRs) to control the vigorous growth of shoot is continuously increasing [7]. Current grower practices often face limitations in PGR application techniques, sometimes causing phytotoxicity, abnormal fruit development, and yield reduction [8,9].

Among available growth regulators, mepiquat chloride (MC) and chlormequat chloride (CCC) offer distinct advantages in restricting shoot growth. MC is a mild but effective growth retardant, which plays a crucial role in regulating plant growth and development. It can inhibit the overgrowth of stems and leaves, shape the ideal plant type, and enhance light utilization efficiency [10,11]. Its mechanism of action involves reducing the concentration of gibberellins and disrupting normal cellular activities, thereby shortening the internode length and reducing the plant height [12]. It has been widely used on cotton cultivation all over the world [13,14]. Preliminary studies in fruit crops suggest MC can enhance fruit quality parameters including berry size and soluble solids content (SSC) as well as decrease shoot growth [15,16,17,18].

CCC is another promising plant growth retardant that is easily degraded in the soil and does not affect soil microbial activity. Its mode of action involves selective inhibition of cell elongation without compromising cell division [19]. Numerous studies have shown that CCC possesses the function of shortening plant internodes, making plants short and strong, thickening stems, and enhancing stress resistance in the production process of grain crops [20,21,22], vegetables [23], fruits [24,25,26,27], medicinal plants [28,29], etc. However, there have been no detailed reports on the effects of MC and CCC on grape growth regulation and fruit quality.

In this study, ‘Shine Muscat’ grapevine was used as the test material and different concentrations of MC and CCC were sprayed on the leaves when the branches showed vigorous growth trend before flowering. The application effects of different treatments were analyzed in order to screen out the optimal treatment that could not only control the growth of new shoots, but also had little effect on the size of clusters and berries. At the same time, this treatment could also improve the quality of grape fruits. The study intends to provide a reference for PGR application to inhibit the vigorous growth of grape shoots and achieve labor-saving in production.

2. Materials and Methods

2.1. Plant Material

The experiment was conducted at the experimental base of the Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural Sciences (CAAS) in 2024. The test material consisted of 11-year-old ‘Shine Muscat’ grapevines planted in north–south oriented rows with a spacing of 2 m × 3 m (plant × row). The trees grow uniformly and are robust with a V-shaped horizontal frame.

2.2. Experimental Design and Treatments

Based on the results of pre-tests obtained from 2021 to 2023, nine treatments were set up in the experiment in 2024 (

Table 1. The treatments of plant growth regulators for ‘Shine Muscat’ grape.

Treatments	Reagent	Concentration
CK (control)	Water	-
A	MC	100 mg/L
B	MC	300 mg/L
C	MC	500 mg/L
D	MC	700 mg/L
E	CCC	100 mg/L
F	CCC	300 mg/L
G	CCC	500 mg/L
H	CCC	700 mg/L

). CK (water), MC with four concentrations (100, 300, 500, and 700 mg/L), and CCC with four concentrations (100, 300, 500, and 700 mg/L) were sprayed on the whole plant leaves until the leaves were dripped at the new shoot growth stage (17 April), the flower-cluster separation stage (26 April), and the flowering stage (6 May), respectively. Each treatment had three replicates using the whole plot as a replication unit and the interval was nine days. Due to the strong control effects observed after a single application, MC 700 mg/L (D) and CCC 700 mg/L (H) treatments were sprayed only once, while other treatments received three applications as scheduled.

2.3. Determination of Fruit Growth Parameters

The new shoot length was measured prior to treatment application at three key phenological stages: new shoot growth stage (17 April), flower-cluster separation stage (26 April), and the flowering stage (6 May).

The cluster length, leaf area opposite to the cluster, and relative chlorophyll content (measured using an SPAD-502 chlorophyll meter) were measured at the flowering stage.

The branch number and the fruit axis length were measured at nine days after the flowering stage, and the branch density was the ratio of the branch number to the fruit axis length.

2.4. Measurement of Fruit Quality

After ripening, representative grape clusters were sampled and transported to the laboratory for quality assessment. The single berry weight was measured with an electronic balance (LT502E, Changshu Tianliang Instrument Co., Ltd., Suzhou, China), which was accurate to 0.01 g. The longitudinal diameter and transverse diameter of 30 berries of each treatment were randomly measured by a vernier caliper (ARZ-1331, Eirezer AG, Qingdao, China), accurate to 0.01 cm. Soluble solids content (SSC) was measured using a portable refractometer (PAL-1, ATAGO, Tokyo, Japan) for three replicates with 10 berries per repeat; titratable acidity (TA) was measured using an acid meter (PAL-Easy ACID2, ATAGO, Tokyo, Japan) for three replicates with 10 berries per repeat. The measurement unit of SSC and TA was %. The solid–acid ratio was the ratio of SSC to TA.

2.5. Statistical Analysis

The experimental data were subjected to comprehensive statistical analysis using Microsoft Excel 2019 for preliminary data organization, Origin 2018 for graphical representations, and One-way ANOVA with Duncan’s multiple comparisons were performed using SPSS 25 for advanced statistical computations at a significance level of 0.05.

3. Results

3.1. Growth of Shoots and Leaves

As shown in

Table 2. Effects of different treatments on shoot length of ‘Shine Muscat’ grape.

Treatments	17 April	26 April			6 May
	Shoot Length (cm)	Shoot Length (cm)	Growth Rate (%)	Compared with CK Increase or Decrease (%)	Shoot Length (cm)	Growth Rate (%)	Compared with CK Increase or Decrease (%)
CK	34.30 ± 7.12 bc	94.85 ± 8.03 a	176.53	0.00	148.10 ± 10.40 a	56.14	0.00
A	37.33 ± 6.32 abc	84.10 ± 13.10 ab	125.15	−51.38	137.00 ± 20.80 a	63.00	6.86
B	39.38 ± 7.09 ab	81.40 ± 7.00 b	106.58	−69.95	122.80 ± 14.90 b	50.95	−5.19
C	41.00 ± 4.75 a	82.80 ± 8.50 b	101.90	−74.63	124.50 ± 12.50 b	50.38	−5.77
D	32.70 ± 4.39 c	67.00 ± 8.00 de	104.89	−71.64	98.70 ± 16.10 cd	47.31	−8.83
E	34.80 ± 4.61 bc	78.20 ± 6.00 bc	124.71	−51.82	114.30 ± 15.00 bc	46.14	−10.00
F	37.20 ± 5.94 abc	73.00 ± 6.30 cd	96.10	−80.43	105.70 ± 12.80 cd	44.89	−11.25
G	42.32 ± 5.24 a	70.20 ± 6.70 de	65.77	−110.76	98.90 ± 7.80 d	40.91	−15.23
H	40.05 ± 3.52 ab	65.10 ± 3.10 e	62.55	−113.98	91.90 ± 9.90 d	41.17	−14.97

Note: The data were mean ± SD (n = 20). Different lowercase letters in the same column indicate significant difference according to Duncan’s multiple range tests (p < 0.05). CK: control, A: MC 100 mg/L, B: MC 300 mg/L, C: MC 500 mg/L, D: MC 700 mg/L, E: CCC 100 mg/L, F: CCC 300 mg/L, G: CCC 500 mg/L, H: CCC 700 mg/L.

, compared to the control (CK), the shoot length growth rate of MC-treated plants exhibited significant reductions at 9 days after the first treatment (17 April), which exhibited a concentration-dependent inhibitory effect, with higher concentrations demonstrating greater efficacy. Following the second treatment (26 April), the growth rate changes showed more variable responses, ranging from −6.86% (A) to 8.83% (D). Similarly, CCC treatments demonstrated more pronounced inhibitory effects after the first and second application. The higher the concentration, the better was the inhibition effect. The results of the third survey (6 May) revealed that all treatments except for (A) treatment resulted in significantly shorter shoot lengths compared to CK. The MC 700 mg/L (D), CCC 500 mg/L (G), and CCC 700 mg/L (H) treatments were particularly notable, indicating their superior growth inhibition efficacy. On the whole, both MC and CCC effectively suppressed new shoot growth of ‘Shine Muscat’ grape, with CCC demonstrating consistently stronger inhibitory effects than MC (Table 2 and Figure 1).

After treatment with MC and CCC, the relative chlorophyll content (SPAD) in most treatments was higher than that of the control (CK), except for the MC 300 mg/L (B) treatment (Figure 2A). The highest SPAD was observed in the CCC 700 mg/L (H) treatment, followed by MC 500 mg/L (C) and CCC 300 mg/L (F) treatments. In contrast, the leaf area opposite to the cluster of all treatments decreased to varying degrees compared to CK (Figure 2B), with CCC exhibiting a more pronounced inhibitory effect. The leaf area of CCC 700 mg/L (H) treatment was relatively small, which was 28.96% lower than that of CK.

3.2. Growth of Clusters and Bunches

Different concentrations of MC and CCC exerted varying effects on the cluster length of ‘Shine Muscat’ grape (Figure 3 and Figure 4). The cluster lengths of MC 100 mg/L (A) and 300 mg/L (B) treatments were slightly higher than that of CK, but there was no significant difference. In contrast, all other treatments significantly reduced cluster length, with the most pronounced inhibition observed in the CCC 700 mg/L (H) treatment, which exhibited the lowest value.

The fruit axis length varied among treatments, with MC 700 mg/L (D) and CCC 700 mg/L (H) treatments showing relatively shorter fruit axes, while CCC 100 mg/L (E) treatment exhibited a longer fruit axis (

Table 3. Effects of different treatments on ‘Shine Muscat’ grape bunch.

Treatments	Fruit Axis Length (cm)	Branch Number (No.)	Branch Density (No./cm)
CK	13.60 ± 1.61 ab	21.10 ± 2.69 cd	1.56 ± 0.19 b
A	13.25 ± 1.23 ab	20.80 ± 2.30 d	1.58 ± 0.20 b
B	12.86 ± 1.10 ab	22.27 ± 2.15 cd	1.73 ± 0.10 ab
C	13.10 ± 1.51 ab	22.30 ± 2.45 cd	1.72 ± 0.25 ab
D	12.27 ± 0.82 b	21.73 ± 2.94 cd	1.77 ± 0.22 a
E	14.00 ± 2.37 a	25.18 ± 2.48 a	1.72 ± 0.14 ab
F	13.30 ± 1.46 ab	22.70 ± 1.70 bcd	1.83 ± 0.27 a
G	13.23 ± 1.15 ab	24.82 ± 2.5 2 ab	1.88 ± 0.12 a
H	12.65 ± 1.68 ab	23.50 ± 2.95 abc	1.87 ± 0.17 a

Note: The data were mean ± SD (n = 20). Different lowercase letters in the same column indicate significant difference according to Duncan’s multiple range tests (p < 0.05). CK: control, A: MC 100 mg/L, B: MC 300 mg/L, C: MC 500 mg/L, D: MC 700 mg/L, E: CCC 100 mg/L, F: CCC 300 mg/L, G: CCC 500 mg/L, H: CCC 700 mg/L.

). In terms of branch number, CCC 100 mg/L (E) treatment displayed the highest value, which was significantly greater than other treatments. All treatments, except for MC 100 mg/L (A) treatment, resulted in higher branch numbers compared to CK. Branch density, calculated from branch number and fruit axis length, was significantly influenced by both MC and CCC treatments. All treatments increased branch density relative to CK, with CCC demonstrating a more pronounced effect. Among MC treatments, 700 mg/L (D) treatment had the highest branch density. Similarly, within CCC treatments, 500 mg/L (G) and 700 mg/L (H) treatments produced the greatest branch densities across all treatments.

3.3. Fruit Quality Parameters

MC and CCC treatments showed different effects on the single berry weight of ‘Shine Muscat’ grape (

Table 4. Effects of different treatments on fruit quality of ‘Shine Muscat’ grape.

Treatments	Single Berry Weight (g)	Longitudinal Diameters (cm)	Transverse Diameters (cm)	Fruit Shape Index
CK	12.18 ± 0.82 bc	2.84 ± 0.03 bc	2.66 ± 0.01 cd	1.07 ± 0.01 de
A	14.08 ± 1.14 a	2.98 ± 0.02 a	2.81 ± 0.02 a	1.06 ± 0.00 e
B	13.29 ± 1.20 ab	3.00 ± 0.03 a	2.79 ± 0.03 a	1.07 ± 0.02 de
C	13.38 ± 1.31 ab	3.01 ± 0.03 a	2.77 ± 0.03 a	1.09 ± 0.02 cd
D	12.49 ± 1.93 bc	2.99 ± 0.05 a	2.62 ± 0.06 d	1.14 ± 0.01 a
E	13.29 ± 1.34 ab	3.06 ± 0.04 a	2.76 ± 0.05 ab	1.11 ± 0.02 bc
F	12.24 ± 1.29 bc	2.91 ± 0.07 b	2.69 ± 0.07 bc	1.08 ± 0.01 de
G	12.85 ± 0.84 ab	2.99 ± 0.04 a	2.67 ± 0.02 cd	1.12 ± 0.02 ab
H	11.41 ± 1.20 c	2.82 ± 0.05 c	2.54 ± 0.03 e	1.11 ± 0.01 bc

Note: The data are mean ± SD (n = 30). Different lowercase letters in the same column indicate significant difference according to Duncan’s multiple range tests (p < 0.05). CK: control, A: MC 100 mg/L, B: MC 300 mg/L, C: MC 500 mg/L, D: MC 700 mg/L, E: CCC 100 mg/L, F: CCC 300 mg/L, G: CCC 500 mg/L, H: CCC 700 mg/L.

). With the exception of CCC 700 mg/L (H) treatment, all other treatments increased single berry weight compared to CK. The MC 100 mg/L (A) treatment had the heaviest berries, with MC treatments generally yielding slightly heavier berries than CCC treatments. The longitudinal diameters exceeded the CK values in all treatments except for CCC 700 mg/L (H), with CCC 100 mg/L (E) treatment showing the maximum longitudinal diameter. The transverse diameters were reduced in MC 700 mg/L (D) and CCC 700 mg/L (H) treatments compared to CK, while other treatments maintained higher values. The fruit shape index ranged from 1.06 to 1.14 across treatments, indicating that the berries maintained an oval shape under all experimental conditions.

The SSC analysis revealed significant treatment effects (Figure 5A). The CCC 100 mg/L (E) treatment achieved the highest SSC, representing a significant increase over all other treatments except for CK. Notably, all remaining treatments showed lower SSC values compared to CK. Regarding TA, all treatments exhibited reduced levels relative to CK (Figure 5B). The most pronounced reduction occurred in the MC 500 mg/L (C) treatment, which showed the lowest TA content among all groups. Except for the CCC 500 mg/L (G) treatment, the solid–acid ratios of all other treatments were higher than that of CK (Figure 5C). Among them, the solid–acid ratios of MC 500 mg/L (C) and CCC 100 mg/L (E) treatments were relatively high, which were 15.94% and 16.24% higher than that of CK, respectively. The flesh firmness measurements showed consistent enhancement across all treatments compared to CK (Figure 5D), and the flesh firmness of CCC 500 mg/L (G) and 700 mg/L (H) treatments were significantly higher than that of other treatments.

3.4. Comprehensive Evaluation of Different Treatments

Principal component analysis (PCA) was performed to evaluate the comprehensive effects of different treatments on growth and fruit quality of ‘Shine Muscat’ grape (

Table 5. Principal component analysis of ‘Shine Muscat’ grape quality evaluation factors.

Principal Component	PC1	PC2	PC3
Eigen value	2.397	2.132	1.416
Variance contribution rate (%)	34.245	30.453	20.226
Cumulative variance contribution rate (%)	34.245	64.698	84.924
Branch density	0.843 *	−0.271	0.116
Relative chlorophyll content	−0.660 *	0.597	0.004
Single berry weight	0.641 *	0.230	−0.476
SSC	−0.057	0.236	0.906 *
TA	0.304	0.843 *	−0.379
Solid–acid ratio	0.211	0.938 *	0.244
Flesh firmness	−0.836 *	−0.041	−0.390

Note: * means the bigger absolute value of each index in all factors.

). The analysis extracted three principal components with a cumulative variance contribution rate of 84.924%, effectively capturing the multidimensional treatment effects. The first principal component (PC1) accounting for 34.245% of the total variance, primarily represented four key traits: branch density, relative chlorophyll content (SPAD), single berry weight, and flesh firmness. The second principal component (PC2) explained 30.453% of the variance and was predominantly associated with TA and the solid–acid ratio. The third principal component (PC3) accounted for 20.226% of the variance and mainly represented the original information of SSC.

The PCA employed the Z value for comprehensive evaluation, where higher values indicated superior overall treatment effects. The ranking of treatments based on composite values was as follows: C > E > A > CK > D > F > B > H > G (

Table 6. The comprehensive evaluation of the effect of different treatments.

Treatments	CK	A	B	C	D	E	F	G	H
Z value	0.315	0.357	−0.294	1.038	0.252	0.92	0.069	−1.571	−1.086
Rank	4	3	7	1	5	2	6	9	8

). The score of MC 500 mg/L (C) treatment was the highest, indicating that the comprehensive effect of MC 500 mg/L (C) treatment was the best, followed by CCC 100 mg/L (E) treatment. On the whole, MC 500 mg/L and CCC 100 mg/L treatments had the best effect on the control effect and comprehensive quality of ‘Shine Muscat’ grape.

4. Discussion

The judicious application of PGRs represents an effective strategy for controlling excessive shoot elongation in grapevines. This often results from multiple interacting factors including (1) abnormal climatic conditions such as reduced diurnal temperature variation and insufficient solar radiation, and (2) suboptimal cultivation practices including excessive irrigation, inadequate canopy ventilation, and imbalanced nitrogen fertilization. Through precise regulation of vegetative growth, these compounds can significantly enhance final fruit quality parameters [30].

Both MC and CCC are growth retardants that primarily act by suppressing gibberellin (GA) biosynthesis, a key phytohormone responsible for cell elongation and stem growth [31]. Previous research demonstrated that pre-flowering applications of MC (500–1500 mg/L) and CCC (500–1500 mg/L) effectively regulate excessive shoot growth in grapevines [32]. Consistent with these findings, our study revealed that sequential pre-flowering applications of both MC (300, 500, 700 mg/L) and CCC (100, 300, 500, 700 mg/L) significantly inhibited vigorous shoot growth in ‘Shine Muscat’ grapevines. These results align with earlier reports by Hanaa and Samia [17] and Ma et al. [23]. The grape cultivar ‘Shine Muscat’ (Vitis vinifera) may have low inherent sensitivity to MC, resulting in insignificant growth suppression of shoots at 100 mg/L. Notably, CCC exhibited superior growth inhibition efficacy compared to MC at equivalent concentrations.

Chlorophyll, as the primary photosynthetic pigment, plays a crucial role in light energy capture and conversion, with its content directly influencing dry matter accumulation in plants. Extensive research demonstrated that CCC application significantly enhanced chlorophyll content in various species, including lilies [33], panax ginseng [29], solanum melongena L. [34], and tomatoes [35], thereby improving photosynthetic efficiency. Similarly, Kashid et al. [36] reported that MC treatment increased chlorophyll content in sunflower. Our findings corroborate these previous observations, showing that both MC (except for 300 mg/L) and CCC treatments increased relative chlorophyll content (SPAD values) in ‘Shine Muscat’ grape leaves. Notably, the CCC 700 mg/L treatment exhibited the most pronounced effect among all tested concentrations.

As plant growth retardants, MC and CCC primarily inhibit cell elongation rather than cell division, resulting in morphological changes characterized by reduced leaf size but increased leaf thickness. Numerous studies have shown that MC and CCC could decrease the leaf area of panax ginseng [29], cotton [37], and soybean [38]. Our findings align with these previous observations, demonstrating that both MC (100, 300, 500, 700 mg/L) and CCC (100, 300, 500, 700 mg/L) treatments significantly reduced leaf area in ‘Shine Muscat’ grapevines. Regarding cluster development, the study revealed concentration-dependent effects: Low MC concentrations (100, 300 mg/L) showed minimal impact on cluster length, while higher MC concentrations (500, 700 mg/L) significantly reduced cluster length. All tested CCC concentrations (100, 300, 500, 700 mg/L) produced substantial decreases in cluster length.

The results of this study showed that sequential application of MC (100, 300, 500 and 700 mg/L) and CCC (100, 300, 500 and 700 mg/L) before flowing could increase the branch density of ‘Shine Muscat’ grape cluster. Appropriately increasing the branch density of ‘Shine Muscat’ grape cluster could make the grape cluster shape more compact, which plays an important role in shaping the standardized cluster shape of ‘Shine Muscat’ grape. Lim et al. [15] proved that MC treatment had a better effect on the berry enlargement of grape. Kaur et al. [24] also found that CCC treatment increased the fruit weight of pears. In this study, it was found that MC and CCC (except for 700 mg/L) increased the fruit size of ‘Shine Muscat’ grape, thereby increasing the yield, which was consistent with the results of previous studies. In addition, the single berry weight decreased with the increase of MC and CCC concentration, but did not reach statistical significance, which was in line with the results of Ma et al. [23] on tomato.

SSC, TA, and solid–acid ratio are important indexes to evaluate fruit quality. The profound effects of MC and CCC on sugar accumulation patterns involve a sophisticated interplay of metabolic regulation, membrane transport modification, and source–sink relationship alteration. Kaur et al. [24] found that CCC (250, 500, and 1000 mg/L) treatments increased the fruit SSC and decreased the TA content of pears, though there was no significant difference with control. Parodi et al. [39] also found that the application of MC had a positive effect on the SSC of avocado. The results of this study showed that CCC 100 mg/L could significantly increase the SSC, and the TA contents of all the treatments were relatively lower than control resulting in higher solid–acid ratios of ‘Shine Muscat’ grape, which was in accordance with the results of previous studies. In this study, no inherent correlation was observed between SSC and grape berry size, which does not align with the results of Kaur et al. [19], whose experiment carried out using different concentrations of CCC on three grape cultivars ‘Perlette’, ‘Flame Seedless’, and ‘Punjab Purple’ grown under a polyhouse. This discrepancy may be attributed to variations in experimental cultivars and environmental conditions.

Fruit firmness serves as a crucial quality parameter that directly impacts both marketability and consumer acceptance. In this study, MC and CCC treatments all could increase the fruit firmness, especially CCC 500 mg/L and CCC 700 mg/L, which was a benefit in increasing the fruit quality. Similar results were found by Pant and Kumar [40] who reported that an apple’s firmness increased with CCC (250, 500, 1000, and 5000 mg/L) sprays. Besides, Chit-aree et al. [41] also found that MC could increase the fruit firmness of longan.

Principal component analysis was used to evaluate the effect comprehensively. Results showed that MC 500 mg/L and CCC 100 mg/L treatments had the best effect on the control effect and comprehensive quality of ‘Shine Muscat’ grape.

5. Conclusions

This experiment proved that spraying MC and CCC at the new shoot growth stage, flower-cluster separation stage, and flowering stage of ‘Shine Muscat’ grape could achieve the purpose of controlling the growth of new shoots, while the effect of CCC was better than that of MC. Although high concentrations of MC and CCC can effectively suppress shoot elongation, they may also significantly impair inflorescence development and berry growth. Extreme caution must be exercised when applying these plant growth regulators. Combined with the practical production, it was suggested to spray MC 500 mg/L or CCC 100 mg/L at the new shoot growth stage, flower-cluster separation stage, and flowering stage of ‘Shine Muscat’ grape to improve the effect of controlling vigorous growth and the nutritional quality of fruits.