Improving Water Use Efficiency, Yield, and Fruit Quality of Crimson Seedless Grapevines under Drought Stress

Abstract

Drought stress is a group of abiotic stresses that affects plant growth and yield production. A field experiment over two successive seasons (2021–2022 and 2022–2023) in sand soil was conducted to investigate the integration effect of deficit irrigation, soil amendment “hundzsoil”, and the spraying of proline on the water use efficiency (WUE), yield, and fruit quality of 8-year-old Crimson seedless table grapes. Four application rates of soil amendment (0, 2, 4, and 6 kg hundzsoil /vine) were added during the dormancy period, and four irrigation levels at 125, 100, 75, and 60% of the field capacity were applied just before flowering until harvest. Proline at two levels (0 and 500 ppm) was applied as a foliar spray. Parameters such as bud fertility, weight of 100 berries, juice volume, and cluster number were positively affected by irrigation at 75% FC along with applying hundzsoil at 2 and 4 kg/vine under proline spray in both seasons. Irrigation at the 125% FC level with a 6 kg hundzsoil application under proline spray resulted in the highest yield, berries number, cluster length, cluster weight, and total anthocyanin in both seasons. The TSS/acidity ratio was significantly and positively affected by deficit irrigation (60% FC level) under hundzsoil at a rate of 4 kg alongside proline spray. Reducing irrigation to 60% FC without hundzsoil and proline spray negatively affected numerous growth parameters and the yield. However, irrigation at 60% FC alongside 6 kg of hundzsoil and proline showed the highest IWUE in both seasons. Proline spray was a key factor in conserving water used for irrigation. This study recommends using deficit irrigation alongside hundzsoil application under proline spray as an adequate strategy for water use efficiency and improving the yield and fruit quality of Crimson seedless grapevines cultivated in sand soil.

1. Introduction

Drought has become a global problem because of climate change, such as rising temperatures and less precipitation [1]. The Middle East and North Africa are the most affected by drought. Drought is a set of abiotic stresses that affects plant growth and yield production in arid and semi-arid regions [2]. Drought reduces global average yield production by more than 50% [3]. Egypt faces external pressures on its water rights, limited availability of national water resources, and a struggle to formulate a sustainable development vision for its future [4]. Egypt implemented management plans to alleviate drought stress, including planting fewer susceptible crops, maintaining water quality, and protecting it from contamination, improving irrigation technologies and controlling irrigation water, and building, operating, and maintaining reservoirs [5]. However, the current policies regarding irrigation on newly reclaimed lands and the current rate of water reuse will not be sufficient to fill in the demand gap in the future [6]. The Egyptian Ministry of Water Resources reported that the agriculture sector in Egypt is consuming around 85% of the available water [7,8]. However, there is a need for too much in some sectors, such as the domestic and industrial sectors. So, there is a limited amount of water available to the agriculture sector that is also limited by climate change caused by an increase in temperature and a decrease in precipitation [9]. Agriculture production is loosened a lot because water is limiting plant growth [9].

Globally, water scarcity is a growing concern, and optimizing water use efficiency (WUE) has become crucial for agricultural and horticultural productions [10]. Water availability is a major challenge in cultivation in arid and semi-arid areas and a limiting factor to cultivation in those areas [11]. Improving WUE in grapevines has become an objective in water management practices. Also, it has become a vital agriculture and food security goal. Grapevine water requirements range from 300 to 700 mm/year [12]. Climatic changes lead to an increase in temperature and a decrease in water availability [13], so there is a need for accurate grapevine irrigation. The use of water deficit irrigation is a strategy to increase grapevine WUE [14,15,16].

The deficit irrigation method is one of the best techniques to rationalize water consumption in the agricultural sector. This method improves the exploitation of soil water by plant roots [17]. On the other hand, Egypt has a land resource shortage, and there is a persistent need to increase land area used for agriculture to feed the country’s expanding population. Most of the land that can be used to expand agricultural operations is in the Egyptian Western Desert which has sandy soil with low physical and chemical properties [18]. Studies have proven the importance of the deficit irrigation strategy in rationalizing water consumption with positive effects on different fruit stages [19]. However, deficit irrigation should be applied during growth periods which are less sensitive to fruit growth [20].

Table grapes are among the most popular fruits produced in Egypt and exported to European Union markets [21]. Grape cultivation is distributed geographically from Alexandria in the north to Aswan in southern Egypt, and this is accompanied by the production of early- and late-ripening grapes during the period from May to October [21]. Crimson seedless (Vitis vinifera L.) is a late-ripening red seedless grape cultivar with superior eating properties and is a bit sweet, firm, and crisp, and the flavor in this variety is the most popular for exports. Meanwhile, poor color and small berry size are the primary fruit quality problems [22]. Grape berry growth is classified as a double sigmoid curve, and the starting of the second sigmoid phase is called veraison [23], where sigma is the initiation of ripening and is very sensitive to irrigation levels [24]. Therefore, the care of water availability during the growing season is one of the critical production factors.

Soil amendments play an important role in improving soil workability, water productivity, and soil fertility [18,25]. Soil amendments improve the number and activity of soil microorganisms [26]. This results in an increase in soil organic matter, nitrogen content, and nutrient availability [27]. The humic compounds in organic matter improve water availability, crop yield, and nutrient availability [28]. Soil amendments improve the sandy soil structure, allowing it to retain more water. This means that the soil becomes a better sponge, holding water for a longer period. This helps plants have a consistent source of water during drought periods [29]. Hundzsoil is a unique soil amendment that has been proven to enhance WUE in agricultural lands. It is made of natural minerals, organic matter, and microorganisms, which work together to improve soil structure, aeration, and water infiltration [30]. Soil, Water, and Environment Research Institute, Egypt, certified hundzsoil as a soil amendment in 2011 [31]. It was found that hundzsoil amendment saves about 15% of irrigated water to achieve the same yield and fruit quality as Flame seedless grapevines under water stress conditions [31]. The quality of Crimson seedless grapevines was improved by soil amendments and organic fertilizers [32].

Osmoprotectant application such as proline increased crop quality and plant tolerance to water stress under drought [33,34,35]. Proline is an amino acid that plays a crucial role in plant response to stress conditions, including drought [36,37,38]. Proline was useful in increasing shoot length and leaf area as well as encouraging yield per vine, cluster weight, berry weight, SSC content, and total anthocyanin while decreasing titratable acidity in berries [39]. Moreover, the total soluble solids (TSSs) and total anthocyanin of the Crimson seedless grape were considerably improved by proline spray [22].

This study aimed to quantitatively save irrigation water and energy in sandy soil while improving the yield and fruit quality of Crimson seedless grapevines. The tested hypotheses were therefore as follows: (1) Would deficit irrigation starting before flowering to harvest alongside treating soil with hundzsoil amendment and proline spray improve the fruit quality of Crimson seedless grapevines? (2) Would Crimson seedless grapevine yield decrease as the irrigation level decreases? (3) Would the above treatments improve the water use efficiency of Crimson seedless grapevines?

2. Materials and Methods

2.1. Experiment Location and Experimental Design

This investigation was conducted during the 2021–2022 and 2022–2023 seasons in a farm vineyard in El-Nobaria city, El-Beheira governments on 80 km at Alexandria–Cairo desert road, Egypt (30°39′45″ N, 30°02′26″ E). The monthly average temperatures and relative humidity for each season are presented in Figure 1. The average annual rainfall was 162 and 168 in 2022 and 2023, respectively. Eight-year-old vines in sand soil spaced at 2 × 3 m, under a drip irrigation system, and trellised by the Spanish Parron system were selected. All grapevines received the same horticultural practices recommended by the Ministry of Agriculture.

The application of the investigated treatments started in 2021. The soil under each vine was treated with a soil amendment named “hundzsoil” at 0, 2, 4, and 6 kg/vine during the dormancy period. The soil amendment dose was mixed manually and carefully with the top 30 cm of the soil under each vine at the beginning of every season. The irrigation levels were 125, 100, 75, and 60% of the field capacity (FC) and started before flowering to harvest. Proline spraying at 0 and 500 ppm concentrations started 15 days after the beginning of irrigation treatments and repeated at 15-day intervals until harvesting. Proline at 500 ppm was investigated in a previous study [22] to alleviate water stress. The total number of three-factorial interactions was 32 treatments.

2.2. Soil and Hundzsoil Analysis

The physical and chemical characteristics of soil and hundzsoil amendment are shown in

Table 1. Some physical and chemical characteristics of the soil.

Soil Physical Characteristics	Value	Soil Chemical Characteristics	Value
Sand	86.28%	pH 1:2.5	8.12
Silt	8.87%	EC (dS/m)	1.90
Clay	4.85%	Ca2+ (mEq/L)	6.50
Soil texture	Sand	Mg2+ (mEq/L)	2.50
Bulk density (kg/m3)	1.55	K+ (mEq/L)	1.00
Field capacity (%)	16.38	Cl− (mEq/L)	2.50
Permanent wilting point (%)	7.90	OM (g·kg−1)	2.00

and

Table 2. Hundzsoil amendment physical and chemical characteristics.

Characteristic	Value	Characteristic	Value
Water holding capacity	270%	pH	6.48
Total nitrogen	0.55%	EC (ds/m)	2.01
Total phosphorus	0.1%	Organic carbon (g·kg−1)	382.4
Total potassium	0.09%	OM (g·kg−1)	659.4

, respectively. Soil and hundzsoil analyses were achieved according to Page [40]. The field capacity and permanent wilting point were measured by the pressure membrane according to Israelson and Hansen [41].

2.3. Determination of Applied Irrigation Water (AIW.mm)

Four levels of water (125, 100, 75, 60% FC) were applied to plants. Irrigation water amounts were calculated according to Vermeiren and Jopling [42].

$$AIW=\frac{ETo\times Kc\times Kr\times I}{Ea}$$

where ETo is the reference evapotranspiration (mm·day⁻¹) calculated according to Allen [43], Kc is the crop factor for grapevines, Kr is the reduction factor depending on crop type, I is the irrigation interval, and Ea is the irrigation efficiency (90%).

Irrigation time was calculated according to Phocaides [44]:

$$t=\frac{(AIW\times A)}{q}$$

where t is the irrigation time (h), A is the area (feddan; 1 hectare = 2.38 feddan), and q is the discharge of the dripper (L.h⁻¹).

2.4. Determination Irrigation Water Use Efficiency (IWUE)

Irrigation water use efficiency was calculated according to Payero et al. [45] as follows:

$$IWUE=\frac{Cropyield\left(\frac{Kg}{Fed}\right)}{Appliedirrigationwater\left(\frac{m^3}{Fed}\right)}$$

2.5. The Studied Vegetative, Physical, and Chemical Properties of Crimson Seedless Grapevines

2.5.1. Studied Vegetative Properties of Crimson Seedless Grapevines

Some growth parameters at growth cessation, such as shoot length and leaf area, were evaluated. Leaf area was measured by a planimeter. Bud fertility percentage was obtained by dividing the average number of clusters per vine by the total number of buds per vine, according to Bessis [46]. On 19 September 2022 and 11 September 2023, vines were harvested, and the total yield per vine was recorded. Six representative clusters per vine were chosen for quality determination. To estimate berry quality parameters at harvest time, an average of one hundred representative berries per replicate was reported for each treatment.

2.5.2. Studied Physical Properties of Crimson Seedless Grapevines

Some physical properties of Crimson seedless grapevines, such as the weight and size of 100 berries, juice volume, berry diameter and length, cluster weight, cluster length and width, and clusters and berries number, were studied. Berry sizes were determined by measuring the volume of water displaced in a measuring cylinder after the addition of berries, and juice volume was calculated by a measuring cylinder. Berry length and diameter were measured using the vernier dermis.

2.5.3. Studied Chemical Properties of Crimson Seedless Grapevines

Some chemical properties of Crimson seedless grapevines, such as TSS, acidity, and total anthocyanin, were studied. For quality determination, six clusters per vine were selected. An average of 100 representative berries per vine for each replicate was reported to estimate berry quality parameters at harvesting time. Berry juice’s TSSs were estimated using a refractometer (model ATC-1, Atago, Co., Tokyo, Japan). Juice titratable acidity (TA) percent as tartaric acid was determined by titration with a 0.1 N sodium hydroxide solution to the endpoint using the phenolphthalein indicator [47]. In addition, the TSS/acid ratio was computed. Total anthocyanin was extracted by acidified ethanol and determined by a spectrophotometer at 535 nm wavelength [48].

2.5.4. Statistical Analysis

The data were subjected to proper statistical analysis according to the design employed in this study. The statistical design of the experiment was a three-factor randomized block design in a split-split plot arrangement, where the main plots were irrigation levels, and subplots were soil amendment levels; however, the proline spraying levels were the sub-subplots. Three replications for each treatment in both seasons were used; each one consisted of five vines. Before the analysis of variance, numerical (i.e., clusters and berries number) and percentage (i.e., bud fertility and TSS/acidity ratio) data using square root and angular transformation were transformed, respectively. A means comparison was carried out using the least significant difference (LSD) at a 0.05 significance level. Data were analyzed according to Gomez and Gomez [49] using SAS (Statistical Analysis System) version 9.1 [50]. Whenever the three-factorial interaction is significant, the results will be presented and discussed regardless of the significance of the main effects or the two-factorial interaction [49].

3. Results

3.1. Vegetative Growth

3.1.1. Shoot Length

The interaction between the studied factors (three-factorial interaction) showed no significant differences among treatments in both seasons (

Table 3. Results summarization of ANOVA test for significance of different treatments.

Factors *	Bud Fertility %		Yield (kg/Vine)		IWUE **		Shoot Length, cm		Leaf Area, cm2		Weight of 100 Berries, g		Juice Volume, mL		Berry Length, mm		Berries Number		Cluster Length, cm
	2022	2023	2022	2023	2022	2023	2022	2023	2022	2023	2022	2023	2022	2023	2022	2023	2022	2023	2022	2023
A	**	**	**	*	**	**	**	**	**	**	**	**	**	**	**	*	NS	NS	*	*
B	**	**	**	**	**	**	**	**	**	**	**	*	**	**	NS	NS	**	**	NS	NS
C	**	**	**	**	**	**	*	**	*	NS	**	**	**	**	**	**	NS	*	**	NS
AB	**	**	**	**	**	**	NS	*	NS	NS	**	NS	**	**	**	NS	**	**	NS	**
AC	**	**	NS	NS	**	*	**	**	**	NS	NS	**	**	**	NS	*	*	NS	**	NS
BC	**	**	NS	*	**	NS	NS	*	NS	NS	NS	NS	NS	NS	NS	NS	**	**	**	NS
ABC	**	**	**	**	**	NS	NS	NS	NS	NS	**	**	**	**	*	NS	**	**	**	**

* A, B, and C mean irrigation levels, hundzsoil, and proline treatments, respectively. ** IWUE—irrigation water use efficiency (kg/m³ water/feddan), * p < 0.05, ** p < 0.01, and NS means nonsignificant difference.

). Concerning the interaction between irrigation and hundzsoil levels, in the first season, there were no significant differences among all interactions. The irrigation level 100% FC, either with or without hundzsoil applications, and 75% FC under 4 or 6 kg hundzsoil/vine gave the highest shoot length; however, the irrigation level 60% FC without hundzsoil applications significantly decreased shoot length in the second season (

Table 4. Effect of interaction between irrigation levels and hundzsoil on some physical and chemical properties and IWUE of Crimson seedless grapevines.

Irrigation Level	Hundzsoil Level, kg/vine	Shoot Length, (cm)	Size of 100 Berries, (mL)		Berry Diameter, (mm)	Acidity	IWUE
		2023	2022	2023	2023	2023	2023
125% FC	0	111.08 g	425.00 d–f	420.00 f	16.00 c	0.57 b	0.58 h
	2	112.08 fg	426.25 d–f	422.50 ef	16.00 c	0.57 b	0.81 e–g
	4	117.58 b–d	435.00 a	430.00 a–c	16.25 bc	0.61 a	0.69 gh
	6	117.41 cd	427.50 c–e	425.00 de	16.50 ab	0.57 b	0.75 f–h
100% FC	0	119.25 a–c	428.75 b–d	425.00 de	16.50 ab	0.57 b	1.00 d–g
	2	120.16 a–c	422.50 f	426.25 c–e	16.00 c	0.56 bc	0.95 d–g
	4	122.00 a	427.50 c–e	423.75 ef	16.75 a	0.57 b	1.01 d–f
	6	119.50 a–c	426.25 d–f	428.75 b–d	16.75 a	0.55 b–e	1.33 c
75% FC	0	116.08 de	431.25 a–c	433.75 a	16.25 bc	0.55 b–d	1.20 cd
	2	118.25 b–d	432.50 ab	430.00 a–c	16.00 c	0.57 b	1.19 cd
	4	120.33 ab	435.00 a	431.25 ab	16.50 ab	0.54 c–e	1.15 cd
	6	119.33 a–c	435.00 a	432.50 ab	16.25 bc	0.57 b	1.88 b
60% FC	0	106.67 h	423.75 ef	431.25 ab	16.00 c	0.53 e	1.09 c–e
	2	111.33 fg	431.25 a–c	430.00 a–c	16.75 a	0.54 de	1.23 cd
	4	111.58 fg	431.25 a–c	430.00 a–c	16.25 bc	0.53 de	2.01 b
	6	114.25 ef	428.75 b–d	431.25 ab	16.00 c	0.53 e	2.91 a

Different small letters range to show the significant differences between values separately for each parameter.

).

Regarding the interaction between irrigation levels and proline spray, the irrigation level 100% FC, with or without proline spray, and the 75% FC level without proline significantly increased shoot length in the first season (

Table 5. Effect of interaction between irrigation levels and proline spray on vegetative, physical, and chemical properties and IWUE of Crimson seedless grapevines.

Irrigation Level	Proline, ppm	Shoot Length, (cm)		Leaf Area, (cm2)	Size of 100 Berries (mL)	Berry Diameter (mm)		Berry Length (mm)	TSS	IWUE
		2022	2023	2022	2023	2022	2023	2023	2023	2023
125% FC	0	112.37 c	112.04 d	152.11 c	423.12 d	15.75 d	15.75 d	22.12 d	19.25 d	0.64 f
	500	116.00 b	117.04 c	152.21 c	425.62 cd	16.62 a	16.62 a	22.50 c	19.62 bc	0.77 ef
100% FC	0	119.16 a	120.12 a	154.25 ab	425.00 cd	16.25 bc	16.50 a	23.12 ab	19.12 d	0.96 de
	500	119.87 a	120.33 a	154.91 a	426.87 c	16.37 a–c	16.50 a	23.12 ab	20.12 a	1.18 c
75% FC	0	119.41 a	118.41 bc	154.50 ab	430.00 b	16.12 c	16.12 bc	22.75 bc	19.50 cd	1.15 cd
	500	116.29 b	118.58 b	153.56 b	433.75 a	16.50 ab	16.37 ab	23.37 a	20.00 ab	1.56 b
60% FC	0	109.62 d	109.37 e	152.08 c	425.62 cd	16.12 c	15.87 cd	22.50 cd	19.75 a–c	1.59 b
	500	111.95 c	112.54 d	150.16 d	435.62 a	16.50 ab	16.62 a	23.12 ab	20.00 ab	2.03 a

Different small letters range to show the significant differences between values separately for each parameter.

). The same pattern was observed in the second season except for irrigation level 75% FC that was with proline spray. In both seasons, shoot length recorded the lower value with irrigation level 60% FC without proline. With respect to the interaction between hundzsoil and proline spray, there were no significant differences in the first season (Table 3); meanwhile, applying hundzsoil at a rate of 4 or 6 kg per vine under proline recorded the greatest shoot length in the second season (

Table 6. Effect of interaction between hundzsoil levels and proline spray on vegetative, physical, and chemical properties of Crimson seedless grapevines.

Hundzsoil Level kg/Vine	Proline, ppm	Shoot Length, (cm)	Berry Diameter, (mm)	TSS		Acidity	TSS/Acidity
		2023	2023	2022	2023	2023	2023
0	0	112.95 c	15.87 c	19.37 bc	19.25 c	0.55 bc	34.75 bc
	500	113.58 c	16.50 ab	19.62 bc	19.37 bc	0.56 a–c	34.78 bc
2	0	114.79 bc	16.00 c	19.50 bc	19.62 b	0.55 bc	35.67 b
	500	116.12 b	16.37 b	19.50 bc	19.62 b	0.57 ab	34.43 cd
4	0	116.20 b	16.37 b	19.75 b	19.25 c	0.58 a	33.42 d
	500	119.54 a	16.50 ab	20.37 a	20.37 a	0.55 bc	37.07 a
6	0	116.00 b	16.00 c	19.25 c	19.50 bc	0.55 c	35.44 bc
	500	119.25 a	16.75 a	20.25 a	20.37 a	0.56 a–c	36.02 ab

Different small letters range to show the significant differences between values separately for each parameter.

). Concerning soil amendment hundzsoil, in the first season, shoot lengths under 4 or 6 kg hundzsoil/vine were remarkably higher than treatments with zero hundzsoil (Figure 2).

3.1.2. Leaf Area

In both seasons, there were no significant differences among three-factorial interaction treatments and two-factorial interactions (irrigation + hundzsoil and hundzsoil + proline) (Table 3). No significant difference was detected among irrigation + proline interactions in the second season (Table 3). Irrigation at 100% FC, with or without proline spray, and 75% FC without proline gave the highest leaf area in the first season (Table 5). Leaf area was significantly increased as affected by 100% FC and 75% FC irrigation treatments, compared with 125% FC and 60% FC treatments in the second season (Figure 2). Regarding soil amendment hundzsoil, in both seasons, leaf areas under 4 or 6 kg hundzsoil were higher than control (zero hundzsoil) (Figure 2).

3.1.3. Bud Fertility%

The data presented in

Table 7. Effect of interaction among irrigation levels, amendment of hundzsoil levels, and proline spray on bud fertility% and yield.

Irrigation Level	Hundzsoil Level, kg/Vine	Proline, ppm	Bud Fertility%		Yield (kg/Vine)
			2022	2023	2022	2023
125% FC	0	0	51.42 a–d	41.90 i–k	12.81 j–l	12.83 c–g
		500	52.37 ab	47.61 c–f	12.19 kl	9.42 h–m
	2	0	46.98 hi	44.12 g–j	16.64 d–h	11.30 e–k
		500	49.83 c–g	46.34 e–g	21.96 b	19.65 a
	4	0	48.88 e–h	44.43 g–i	18.41 c–e	13.62 c–f
		500	53.33 a	46.97 d–g	17.92 c–f	12.83 c–g
	6	0	47.61 g–i	47.93 c–f	16.85 d–g	11.74 d–j
		500	46.67 hi	41.90 i–k	25.41 a	17.08 ab
100% FC	0	0	42.53 j–l	41.26 jk	12.63 kl	10.44 f–l
		500	53.33 a	48.56 b–e	21.09 bc	15.94 bc
	2	0	49.51 d–g	41.90 i–k	12.70 kl	9.22 i–m
		500	53.33 a	51.42 ab	14.65 g–k	13.46 c–f
	4	0	52.06 a–c	41.90 i–k	18.22 c–f	12.46 d–i
		500	52.06 a–c	47.61 c–f	19.54 b–d	12.86 c–g
	6	0	52.06 a–c	46.34 e–g	15.03 f–k	11.48 d–k
		500	52.06 a–c	46.98 d–g	15.98 e–j	11.98 d–j
75% FC	0	0	52.69 a	48.25 c–e	16.04 e–j	10.07 g–l
		500	53.33 a	47.61 c–f	16.75 d–g	13.67 c–e
	2	0	52.06 a–c	49.52 a–d	14.10 g–k	8.89 j–n
		500	53.33 a	52.37 a	16.33 d–i	12.57 d–i
	4	0	45.70 i	39.99 k	13.32 i–k	8.29 k–n
		500	53.33 a	50.47 a–c	18.85 b–e	13.39 c–f
	6	0	46.98 hi	44.44 g–i	13.91 g–k	11.31 e–k
		500	52.06 –c	47.61 c–f	18.63 c–e	13.51 c–f
60% FC	0	0	29.52 m	28.56 m	8.56 m	6.48 mn
		500	30.15 m	27.93 m	11.84 kl	7.92 l–n
	2	0	40.63 l	35.55 l	9.70 lm	5.88 n
		500	40.94 kl	35.86 i	14.09 g–k	8.91 j–n
	4	0	46.98 hi	42.53 h–k	16.90 d–g	10.73 e–l
		500	50.15 b–f	47.61 c–f	18.96 b–e	14.62 b–d
	6	0	48.25 f–h	45.07 f–h	13.45 h–k	11.92 d–j
		500	48.25 f–h	45.71 e–g	18.49 c–e	13.72 c–e

Different small letters range to show the significant differences between values separately for each parameter.

showed that, in the first season, 15 treatments had a superior effect and recorded the greatest bud fertility percent, named as follows: treatment (125% FC), irrigation at 125% FC interacting with hundzsoil and proline (125% FC + proline and 125% FC + 4 kg hundzsoil/vine + proline), six interactions with irrigation at 100% FC (100% FC + proline, 100% FC + 2 kg hundzsoil/vine + proline, and 100% FC + 4 or 6 kg hundzsoil/vine ± proline), and irrigation at 75% FC in six interactions (75% FC without hundzsoil or proline, 75% FC + proline, 75% FC + 2 kg hundzsoil/vine ± proline, and 75% FC + 4 or 6 kg hundzsoil/vine + proline). All previous mentioned treatments had no significant differences among them, indicating that treatment with an irrigation level of 75% FC without hundzsoil or proline would be the profitable one in improving bud fertility%.

In the second season, four treatments (100% FC + 2 kg hundzsoil/vine + proline, 75% FC + 2 kg hundzsoil/vine ± proline, and 75% FC + 4 kg hundzsoil/vine + proline) recorded the highest bud fertility percent. The preferable treatment was an irrigation level of 75% FC + 2 kg hundzsoil/vine without proline spray. On the other hand, the treatments with irrigation levels of 60% FC without hundzsoil and vines treated with or without proline spray had the lowest values in both seasons. Some other treatments were on the second turn of improving bud fertility with deficit irrigation such as 60% FC + 4 or 6 kg hundzsoil/vine + proline in both seasons (Table 7).

3.1.4. Yield

The obtained results indicated that, in the first season, the irrigation level at 125% FC + 6 kg hundzsoil/vine + proline spray had the highest yield. In the second season, vines treated with irrigation level 125% FC + 2 or 6 kg hundzsoil + proline resulted in the highest yield. Those treatments were followed by another group of treatments such as irrigation at 75% and 60% of FC + 4 or 6 kg hundzsoil/vine once proline spray was applied in both seasons. However, the 60% FC irrigation level without hundzsoil or proline spray and 60% FC + 2 kg hundzsoil/vine without proline spray recorded the lowest yield in the 2022 and 2023 seasons, respectively (Table 7).

3.2. Physical Properties

3.2.1. Weight of 100 Berries

The three-factorial interaction treatments, such as 125% FC + 4 kg hundzsoil/vine + proline, 75% FC + 2, 4, or 6 kg hundzsoil/vine + proline, 75% FC + 6 kg hundzsoil/vine without proline, and 60% FC + 2 or 6 kg hundzsoil/vine + proline, resulted in higher weights of 100 berries in the first season (

Table 8. Effect of interaction among irrigation levels, hundzsoil, and proline spray on some physical properties of Crimson seedless grapevines.

Irrigation Level	Hundzsoil Level kg/Vine	Proline ppm	Weight of 100 Berries (g)		Juice Volume (mL)		Berry Length (mm)	Berries Number
			2022	2023	2022	2023	2022	2022	2023
125% FC	0	0	462.33 e–g	460.00 e	370.00 g	370.00 g	22.00 d	67.67 h–n	65.67 f–l
		500	465.00 d–f	460.00 e	375.00 ef	370.00 g	22.00 d	47.33 o	36.33 m
	2	0	462.33 e–g	462.67 de	372.33 fg	372.33 fg	22.00 d	76.33 f–j	85.00 b–e
		500	467.33 c–e	462.33 de	380.00 cd	377.33 e	22.33 cd	104.00 ab	83.00 b–f
	4	0	470.00 b–d	467.33 b–d	380.00 cd	377.33 e	22.00 d	94.33 a–e	79.00 b–g
		500	472.33 a–c	465.00 c–e	390.00 ab	385.00 cd	22.33 cd	86.00 c–g	60.00 h–l
	6	0	465.00 d–f	462.67 de	377.33 de	372.67 fg	22.33 cd	74.33 f–l	77.67 b–h
		500	470.00 b–d	467.33 b–d	380.00 cd	377.67 e	23.00 bc	106.67 a	110.00 a
100% FC	0	0	467.67 c–e	460.00 e	377.33 de	372.67 fg	23.00 bc	71.33 f–m	68.33 e–l
		500	470.00 b–d	467.33 b–d	377.67 de	375.00 ef	23.67 ab	97.00 a–d	92.00 a–d
	2	0	460.00 fg	467.33 b–d	380.00 cd	377.33 e	23.67 ab	71.00 f–n	59.33 h–l
		500	460.00 fg	462.67 de	375.00 ef	375.00 ef	24.00 a	54.33 m–o	55.00 kl
	4	0	465.00 d–f	462.33 de	375.00 ef	372.33 fg	23.00 bc	101.00 a–c	95.67 ab
		500	470.00 b–d	465.00 c–e	380.00 cd	375.00 ef	23.00 bc	60.67 j–o	64.67 g–l
	6	0	465.00 d–f	467.67 b–d	377.33 de	377.67 e	22.33 cd	69.33 g–n	58.33 i–l
		500	467.67 c–e	470.00 a–c	382.33 c	382.67 d	23.67 ab	57.33 l–o	64.00 g–l
75% FC	0	0	470.00 b–d	475.00 a	380.00 cd	382.33 d	22.67 cd	83.67 c–h	92.00 a–d
		500	465.00 d–f	467.33 b–d	387.33 b	387.33 bc	23.33 ab	58.67 k–o	60.00 h–l
	2	0	467.33 c–e	467.67 b–d	380.00 cd	377.67 e	23.00 bc	53.33 no	69.00 e–l
		500	475.00 ab	472.67 ab	392.00 a	392.33 a	24.00 a	67.33 h–n	59.00 i–l
	4	0	470.00 b–d	465.00 c–e	382.67 c	377.33 e	22.33 cd	86.00 c–g	107.00 a
		500	477.33 a	475.00 a	392.33 a	392.67 a	23.33 ab	76.00 f–k	73.67 e–j
	6	0	472.67 a–c	470.00 a–c	382.33 c	382.67 d	23.00 bc	64.67 i–o	57.00 j–l
		500	477.33 a	475.00 a	387.67 b	390.00 ab	23.00 bc	80.33 d–i	76.00 d–i
60% FC	0	0	457.30 g	462.33 de	372.33 fg	372.33 fg	22.33 cd	72.33 f–l	68.33 e–l
		500	467.67 c–e	472.33 ab	382.67 c	385.00 cd	24.00 a	74.33 f–l	61.33 g–l
	2	0	465.00 d–f	465.00 c–e	377.33 de	372.67 fg	22.00 d	80.00 d–i	68.00 e–l
		500	475.00 ab	470.00 a–c	390.00 ab	382.33 d	23.00 bc	72.33 f–l	85.67 b–e
	4	0	470.00 b–d	462.67 de	382.67 c	377.33 e	22.33 cd	75.67 f–k	94.67 a–c
		500	465.00 d–f	467.67 b–d	382.33 c	385.00 cd	22.67 cd	88.00 b–f	76.33 c–i
	6	0	462.33 f–g	462.33 de	377.33 de	377.67 e	22.33 cd	63.33 i–o	54.00 lm
		500	472.33 a–c	475.00 a	382.33 c	387.67 bc	23.33 ab	77.67 e–j	72.33 e–k

Different small letters range to show the significant differences between values separately for each parameter.

). The lower weights of 100 berries were recorded with treatment (125% FC) and treatments which did not receive proline such as 125% FC or 100% FC + 2 kg hundzsoil/vine, 60% FC, and 60% FC + 6 kg hundzsoil/vine (Table 8). The rest of the treatments, which did not result in either higher or lower weights of 100 berries, showed no significant differences among numerous three-factorial interactions.

In the second season, the nearly higher weights of 100 berries were given by those treatments under deficit irrigation and proline spray regardless of hundzsoil application (Table 8). However, treatments mostly without proline application, such as 125% FC without or with 2 kg hundzsoil/vine ± proline, 125% FC + 6 kg hundzsoil/vine, 100% FC, 100% FC + 6 kg hundzsoil/vine ± proline, 75% FC + 4 kg hundzsoil/vine, and 60% FC ± hundzsoil, resulted in lower weights of 100 berries. The remaining treatments showed irregular patterns of effect.

3.2.2. Size of 100 Berries

The ANOVA test showed no significant differences among treatments regarding three-factorial and two-factorial interactions in both seasons (

Table 9. Results summarization of ANOVA test for significance of different treatments.

Factors	Cluster Width, cm		Cluster Number		Cluster Weight, g		Size of 100 Berries, mL		Berry Diameter, mm		Total Anthocyanin (mg/100 g)		TSS %		Acidity %		TSS/Acidity
	2022	2023	2022	2023	2022	2023	2022	2023	2022	2023	2022	2023	2022	2023	2022	2023	2022	2023
A	**	**	**	**	**	*	**	**	NS	**	NS	*	**	NS	**	**	**	**
B	NS	NS	**	**	**	**	**	NS	*	NS	**	**	**	**	NS	NS	**	NS
C	**	**	**	**	**	**	**	**	**	**	**	**	**	**	NS	NS	NS	*
AB	*	**	**	**	**	**	*	*	NS	*	**	**	NS	NS	*	*	NS	NS
AC	NS	NS	**	**	NS	NS	NS	**	*	**	**	**	NS	*	**	NS	NS	NS
BC	**	*	**	**	NS	*	NS	NS	NS	*	**	**	**	**	**	*	**	**
ABC	**	**	**	**	**	**	NS	NS	NS	NS	**	**	NS	NS	*	NS	*	NS

* A, B, and C mean irrigation levels, hundzsoil, and proline treatments, respectively. ** IWUE—irrigation water use efficiency (kg/m³ water/feddan), * p < 0.05, ** p < 0.01, and NS means nonsignificant difference.

). Furthermore, the interaction between irrigation levels and proline spray showed a nonsignificant difference in the first season. Irrigation levels 125% FC and 75% FC under 4 kg hundzsoil/vine and 75% + 6 kg hundzsoil/vine had the highest size of 100 berries in the first season.

Nevertheless, 75% of the FC without hundzsoil gave the greatest size of 100 berries in the second season (Table 4). The irrigation level at 60% FC + proline spray recorded the highest size of 100 berries only in the second season, but it did not significantly differ from 75% FC + proline spray (Table 5). With respect to proline spray, the size of 100 berries was significantly increased by proline spray as compared to the untreated vines in the first season (Figure 3).

3.2.3. Juice Volume

The results presented in Table 8 showed that treatments 125% FC + 4 kg hundzsoil/vine, 75% FC + 2 or 4 kg hundzsoil/vine, and 60% FC + 2 kg hundzsoil/vine significantly increased juice volume in the first season and 75% FC with hundzsoil at all studied rates of application in the second season once vines were treated with proline. Also, juice volume was affected positively by some other treatments with deficit irrigation under proline spray regardless of hundzsoil treatment in both seasons. Lower juice volume values were observed in the first season for vines untreated either with hundzsoil or proline and irrigated at a level of 125% FC and 60% FC. Similarly, treatments which did not receive proline spray and irrigated at 125% FC without or with hundzsoil at a rate of 2 or 6 kg per vine and irrigation levels 100% FC and 60% FC without or with hundzsoil at a rate of 6 and 2 kg per vine, respectively, gave lower juice volume values in the second season.

3.2.4. Berry Length

There were no significant differences regarding hundzsoil applications or the interaction between hundzsoil and proline in both seasons (Table 3). Moreover, in the second season, there was a nonsignificant difference regarding the two-factorial interaction between irrigation and hundzsoil application. In the first season, treatments with proline spray such as (100% FC + 0, 2, or 6 kg hundzsoil/vine), (75% FC + 0, 2, or 4 kg hundzsoil/vine), and (60% FC + 0 or 6 kg hundzsoil/vine) showed the greatest berry length values (Table 8). There were remarkable differences among treatments regarding the interaction between irrigation levels and proline spray in the second season (Table 3). The irrigation at 60% FC, 75% FC, and 100% FC plus proline spray improved berry length compared with 125% FC without proline in the second season (Table 5).

3.2.5. Berry Diameter

In both seasons, there were no significant differences among three-factorial interaction treatments (Table 9). However, the irrigation at 125% FC + 6 kg hundzsoil/vine, 100% FC without hundzsoil, 100% FC + 4 or 6 kg hundzsoil/vine, 75% FC + 6 kg hundzsoil/vine, and 60% FC + 2 kg of hundzsoil/vine had a remarkably higher berry diameter than the other two-factorial interactions (irrigation + hundzsoil) only in the second season (Table 4). In both seasons, vines irrigated at all levels with proline spray resulted in a greater berry diameter (Table 5). The application of hundzsoil at a rate of 4 and 6 kg under proline spray gave a remarkably higher berry diameter than control (without hundzsoil and proline) in the second season (Table 6). With respect to hundzsoil application, the size of 100 berries was significantly decreased and affected by hundzsoil as compared to the untreated vines in the first season (Figure 4).

3.2.6. Cluster Length and Width

The presented data in

Table 10. Effect of interaction among irrigation levels, hundzsoil, and proline spray on cluster length, cluster width, clusters number, and cluster weight of Crimson seedless grapevines.

Irrigation Level	Hundzsoil Level kg/Vine	Proline ppm	Cluster Length (cm)		Cluster Width (cm)		Clusters Number		Cluster Weight (g)
			2022	2023	2022	2023	2022	2023	2022	2023
125% FC	0	0	19.50 a	18.00 b–d	12.50 b–d	11.00 d–f	54.00 a–d	44.00 i–k	238.33 j–l	291.67 bc
		500	15.50 e–g	14.50 gh	11.00 ef	9.00 g	55.00 a–c	50.00 c–f	221.67 l	188.33 g–i
	2	0	17.50 a–e	17.00 c–e	13.50 ab	13.00 a–c	49.33 hi	46.33 g–j	338.33 c–e	244.16 b–g
		500	16.00 d–g	17.00 c–e	12.50 b–d	12.00 b–e	52.33 c–g	48.67 e–g	420.00 b	404.16 a
	4	0	17.00 b–f	16.50 d–f	13.00 a–c	11.50 c–f	51.33 e–h	46.67 g–i	358.33 c	293.33 bc
		500	17.50 a–e	17.00 c–e	12.00 c–e	11.50 c–f	56.00 a	49.33 d–g	320.00 c–h	260.00 b–f
	6	0	18.50 a–c	18.50 a–c	13.50 ab	13.50 ab	50.00 g–i	50.33 c–f	336.67 c–e	233.33 c–h
		500	18.50 a–c	19.00 ab	12.50 b–d	12.00 b–e	49.00 hi	44.00 i–k	518.33 a	388.33 a
100% FC	0	0	17.00 b–f	17.50 b–e	12.00 c–e	12.00 b–e	44.67 j	43.33 jk	281.67 e–k	240.83 c–g
		500	17.50 a–e	18.00 b–d	13.50 ab	12.00 b–e	56.00 a	51.00 b–e	376.67 bc	310.00 b
	2	0	18.00 a–d	16.50 d–f	12.80 a–d	10.50 e–g	52.00 d–g	44.00 i–k	243.16 i–l	210.00 e–i
		500	15.00 fg	15.00 f–h	9.00 g	9.00 g	56.00 a	54.00 ab	261.67 i–l	248.33 b–g
	4	0	19.00 ab	17.50 b–e	11.50 de	11.50 c–f	54.67 a–c	44.00 i–k	333.33 c–f	283.33 b–d
		500	14.50 g	14.00 h	10.00 fg	10.50 e–g	54.67 a–c	50.00 c–f	357.50 c	257.50 b–f
	6	0	15.00 fg	17.50 b–e	10.00 fg	11.00 d–f	54.67 a–c	48.67 e–g	275.00 g–l	236.67 c–h
		500	15.50 e–g	16.50 d–f	11.00 ef	11.00 d–f	54.67 a–c	49.33 d–g	293.33 d–j	243.33 b–g
75% FC	0	0	17.50 a–e	18.00 b–d	12.00 c–e	13.50 ab	55.33 a	50.67 c–e	290.00 d–j	198.33 f–i
		500	16.50 c–g	18.50 a–c	12.00 c–e	12.00 b–e	56.00 a	50.00 c–f	299.16 d–i	273.33 b–e
	2	0	18.00 a–d	17.00 c–e	12.00 c–e	11.00 d–f	54.67 a–c	52.00 a–d	256.67 i–l	171.67 hi
		500	16.50 c–g	16.00 e–g	11.50 de	10.00 fg	56.00 a	55.00 a	291.67 d–j	228.33 c–h
	4	0	17.50 a–e	16.00 e–g	11.50 de	11.00 d–f	48.00 i	42.00 k	278.33 f–l	198.33 f–i
		500	17.50 a–e	18.00 b–d	12.00 c–e	11.50 c–f	56.00 a	53.00 a–c	336.67 c–e	252.50 b–g
	6	0	16.00 d–g	16.00 d–f	13.00 a–c	13.00 a–c	49.33 hi	46.67 g–i	281.67 e–k	242.50 b–g
		500	16.50 c–g	17.00 c–e	11.50 de	11.00 d–f	54.67 a–c	50.00 c–f	340.00 cd	270.00 b–e
60% FC	0	0	18.50 a–c	17.50 b–e	14.00 a	11.00 d–f	31.00 k	30.00 m	276.50 f–l	216.33 d–i
		500	17.50 a–e	16.50 d–f	13.50 ab	12.20 b–d	31.67 k	29.33 m	373.33 bc	270.00 b–e
	2	0	18.50 a–c	20.00 a	13.00 a–c	14.50 a	42.67 j	37.33 l	227.50 kl	156.67 i
		500	18.50 a–c	17.50 b–e	11.00 ef	10.00 fg	43.00 j	37.67 l	327.50 c–g	235.00 c–h
	4	0	17.00 b–f	17.00 c–e	12.00 c–e	13.50 ab	49.33 hi	44.67 h–k	343.33 cd	240.00 c–h
		500	18.00 a–d	18.50 a–c	13.00 a–c	12.50 b–d	52.67 b–f	50.00 c–f	360.00 c	292.333 bc
	6	0	17.00 b–f	16.50 d–f	13.00 a–c	11.00 d–f	50.67 f–h	47.33 f–h	265.00 h–k	250.00 b–g
		500	19.00 ab	18.50 a–c	12.00 c–e	12.00 b–e	50.67 f–h	48.00 e–g	365.00 bc	285.83 bc

Different small letters range to show the significant differences between values separately for each parameter.

revealed that treatments such as (125% FC), 125% + 6 kg hundzsoil/vine ± proline, 100% FC + 2 or 4 kg hundzsoil/vine without proline, 75% FC + 2 kg hundzsoil/vine without proline, 60% FC without or with 2 kg hundzsoil/vine, and 60% + 2, 4, or 6 kg hundzsoil/vine + proline spray gave the greatest cluster length in the first season; however, that was with treatments like 125% FC + 6 kg hundzsoil/vine ± proline, 75% FC + only proline, 60% FC + 2 kg hundzsoil/vine, and 60% FC + 4 or 6 kg hundzsoil/vine + proline spray in the second season. Further, other treatments with deficit irrigation levels (75% and 60% of the FC) positively affected cluster length in the second season. The irrigation levels 125% FC + 6 kg hundzsoil/vine and without proline and 60% + 2 kg hundzsoil/vine without proline recorded the highest cluster width in both seasons. In the second season, other treatments with lower irrigation levels and containing proline spray standing on the second turn positively affected cluster width (Table 10).

3.2.7. Clusters and Berries Number

Over both seasons, treatments with proline spray such as 100% FC + 2 kg hundzsoil/vine and 75% FC + 2 or 4 kg hundzsoil/vine had the greatest clusters number, while irrigation level 60% FC without hundzsoil ± proline gave the lowest values (Table 10). Also, more results can be stated as follows: 60% FC + treatment 4 kg hundzsoil/vine + proline recorded cluster numbers 52.67 and 50 in the first and second season, respectively, and treatments in which vines were treated with proline spray regardless of the irrigation level or hundzsoil dose positively affected the clusters number (Table 10).

The irrigation at 125% FC + 2 or 6 kg hundzsoil/vine + proline, 125% FC + 4 kg hundzsoil/vine, 100% FC + only proline, and 100% FC + 4 kg hundzsoil/vine treatments in the first season; and 125% FC + 6 kg hundzsoil/vine + proline and 100% FC + only proline spray; and treatments without proline such as 100% FC + 4 kg hundzsoil/vine, 75% FC without hundzsoil, and 75% FC or 60% FC + 4 kg hundzsoil/vine in the second season gave the greatest berries number (Table 8).

3.2.8. Cluster Weight

The irrigation level 125% FC + 2 kg or 6 kg hundzsoil/vine + proline spray recorded the greatest cluster weight, while treatments such as 125% FC without hundzsoil + proline, 100% FC + 2 kg hundzsoil/vine without proline, 75% FC without or with 2 kg or 4 kg hundzsoil/vine and without proline spray, and 60% FC without or with 2 kg hundzsoil/vine and without proline application gave the lowest values in both seasons (Table 10). Furthermore, treatments with the 60% FC irrigation level along with proline in the 2022 season and 60% FC + 4 kg or 6 kg hundzsoil/vine + proline spray in the second season recorded high cluster weight values.

3.3. Chemical Properties

3.3.1. Total Soluble Solids (TSSs)

The interaction among irrigation levels, hundzsoil doses, and proline spray showed nonsignificant differences (Table 9). Also, no significant differences were observed regarding the interaction between irrigation levels and hundzsoil in both seasons (Table 9). For the interaction between irrigation levels and proline spray, 100% FC + proline spray significantly had higher TSSs than 125% FC without proline spray in the second season (Table 5). Regarding the interaction between hundzsoil and proline, 4 kg of hundzsoil/vine + proline spray resulted in the considerably highest TSSs with no significant differences from 6 kg of hundzsoil/vine + proline spray treatments in both seasons (Table 6). All irrigation treatments had highly improved TSSs compared with the treatment (125% FC) in the first season (Figure 5).

3.3.2. Acidity

Concerning the interaction among irrigation, hundzsoil, and proline spray, there were nonsignificant differences among treatments in the second season (Table 9); however, in the first season, treatments such as 60% FC without hundzsoil but with proline, 60% FC + 4 kg hundzsoil/vine + proline, and 60% FC + 6 kg hundzsoil/vine without proline had the significantly lowest acidity (

Table 11. Effect of interaction among irrigation levels, hundzsoil, and proline spray on some chemical properties of Crimson seedless grapevines.

Irrigation Level	Hundzsoil Level kg/Vine	Proline ppm	Total Anthocyanin (mg/100 g)		Acidity %	TSS/Acidity
			2022	2023	2022	2022
125% FC	0	0	14.23 mn	15.47 mn	0.60 ab	31.67 k
		500	25.39 h–l	28.85 h	0.58 a–e	32.48 jk
	2	0	16.07 mn	13.93 n	0.60 ab	32.53 jk
		500	18.85 k–n	20.56 j–l	0.56 c–h	34.51 d–j
	4	0	14.52 mn	16.23 l–n	0.58 a–e	33.70 f–k
		500	29.82 f–i	31.30 gh	0.59 a–c	33.64 g–k
	6	0	22.72 i–m	22.70 ij	0.57 a–f	33.04 i–k
		500	59.88 a	69.16 a	0.55 e–i	36.08 b–f
100% FC	0	0	38.11 c–f	31.46 gh	0.53 h–j	36.44 b–e
		500	21.52 i–m	23.28 ij	0.59 a–d	33.90 f–k
	2	0	39.58 c–e	37.84 ef	0.58 a–e	33.33 h–k
		500	27.53 g–k	28.59 h	0.55 e–i	35.16 c–i
	4	0	22.94 i–m	29.10 h	0.57 b–g	34.22 e–j
		500	22.10 i–m	23.52 ij	0.54 g–j	37.95 b
	6	0	28.19 g–j	27.32 hi	0.55 e–i	34.24 e–j
		500	32.08 e–h	34.55 fg	0.57 a–f	35.70 b–h
75% FC	0	0	35.29 d–g	27.04 hi	0.54 g–j	36.12 b–f
		500	41.76 cd	45.25 c	0.58 a–e	34.48 d–j
	2	0	15.16 mn	16.54 k–n	0.55 e–i	35.13 c–i
		500	27.25 g–k	30.02 gh	0.56 c–h	34.63 d–j
	4	0	21.77 i–m	20.63 j–l	0.54 f–j	36.79 b–d
		500	19.37 j–n	21.46 jk	0.54 f–j	37.61 b
	6	0	22.35 i–m	19.91 j–m	0.54 f–j	35.79 b–g
		500	34.87 d–g	40.05 de	0.60 a	33.87 f–k
60% FC	0	0	18.25 l–n	20.44 j–l	0.52 jk	37.69 b
		500	52.86 ab	57.42 b	0.53 ij	36.80 b–d
	2	0	45.51 bc	44.48 cd	0.55 e–i	35.16 c–i
		500	27.92 g–j	31.81 gh	0.56 d–i	34.83 d–j
	4	0	20.74 j–n	19.45 j–m	0.54 f–j	36.69 b–d
		500	22.31 i–m	22.52 ij	0.49 k	41.40 a
	6	0	12.60 n	14.36 n	0.52 jk	37.51 bc
		500	25.92 h–l	27.00 hi	0.54 f–j	36.71 b–d

Different small letters range to show the significant differences between values separately for each parameter.

). With respect to the interaction between irrigation levels and hundzsoil, 125% FC + 4 kg hundzsoil/vine recorded the remarkably greatest acidity, while 60% FC + 0, 4, or 6 kg hundzsoil/vine gave the lowest value in the second season (Table 4). Concerning the interaction between hundzsoil and proline, 2 kg of hundzsoil with proline spray and 4 kg of hundzsoil without proline recorded the highest acidity in the second season (Table 6).

3.3.3. TSS/Acidity

Regarding the interaction among irrigation, hundzsoil, and proline spray, the 60% FC + 4 kg hundzsoil + proline spray treatment significantly resulted in the greatest TSS/acidity ratio in the first season (Table 11). However, other treatments with deficit irrigation levels either with or without hundzsoil and mostly without proline spray resulted in a high TSS/acidity ratio. Concerning the interaction between hundzsoil and proline spray, 4 or 6 kg of hundzsoil/vine under proline spray had the highest TSS/acidity ratio in the second season (Table 6). Proline spray considerably improved the TSS/acidity ratio as compared to the unsprayed vines in the second season (Figure 5).

3.3.4. Total Anthocyanin

The data presented in Table 11 showed that irrigation level 125% FC + 6 kg hundzsoil + proline caused the remarkably highest total anthocyanin in both seasons, with no significant difference from 60% FC without hundzsoil + proline spray only in the first season. The later treatment occupied second place in the second season and was followed by 75% FC without or with 6 kg hundzsoil/vine + proline. On the contrary, treatments which did not include proline spray such as 125% FC without hundzsoil, with 2 or 4 kg hundzsoil/vine, 75% FC + 2 kg hundzsoil/vine, and 60% FC + 6 kg hundzsoil/vine resulted in lower values (Table 11).

3.4. Irrigation Water Use Efficiency (IWUE)

Figure 6 shows the IWUE for different treatments for the first season. Mostly, as the amount of irrigation decreased, the IWUE increased. The 60% FC, 6 kg hundzsoil with proline spray treatment gave the remarkably highest IWUE in the first season, while the lowest IWUE happened in non-stressed water treatments, which irrigated at 125% FC and was untreated with proline regardless of the hundzsoil application rate. The three-factorial interaction and two-factorial interaction between hundzsoil doses and proline spray showed nonsignificant differences in the second season (Table 3). The interaction between irrigation levels and hundzsoil doses significantly affected the IWUE of Crimson seedless grapevines in the second season. The irrigation at 60% FC + 6 kg hundzsoil/vine significantly increased the IWUE recording the highest value and was followed by 60% FC + 4 kg hundzsoil/vine and 75% + 6 kg hundzsoil/vine (Table 4). Regarding the two-factorial interaction between irrigation levels and proline spray, the highest IWUE was observed with the 60% FC irrigation level alongside proline spray (Table 5).

4. Discussion

This study exhibited how 32 interactions among irrigation levels, hundzsoil treatments, and proline spray affected the irrigation water use efficiency (IWUE), growth characteristics, and yield of Crimson seedless grapevines. Many interesting findings were obtained in this study. The following paragraphs will explain the effect of all studied factors on the water use efficiency and fruit quality of Crimson seedless table grapes.

The veraison stage signals the starting of ripening and is very responsive to irrigation regimes [24,51]. Crimson seedless grapevines had a higher water use efficiency and yield under deficit irrigation conditions [51]. The vines which were subjected to severe deficit irrigation or excess irrigation decreased the photosynthetic rate [52] and accordingly unfavorably influenced vine yield [53]. Berry growth was negatively affected by water stress, and this effect was reliant on the level and time of deficit [54,55,56]. Deficit irrigation controlled the redistribution of photoassimilates through a reduction in vigor with a considerable effect on light interception in the cluster zone and the berry composition [57]. Deficit irrigation encouraged the accumulation of total solids in grape berries [24,58] because of the decreasing leaf area and redirecting of carbohydrates to berries and, at the same time, water loss from deficient berries [59] and/or the advancement of berry ripening by improving the abscisic acid (ABA) indicator for berries [60].

The titratable acidity (TA) percent of grapes with irrigation deficiency is reduced [61]. This effect may be a result of a decrease in tartaric and/or malic acid due to reduced canopy growth and, thus, a higher exposure of the bunches to sunlight, resulting in a greater rate of malic acid breakdown [62,63]. This explained our achievements regarding the reduction in the acidity of Crimson berries as affected by deficit irrigation. The anthocyanin synthesis pathway was positively affected by water stress due to phenolic compound increases [64,65]. Moreover, anthocyanin is a diverse class of flavonoids composed of an anthocyanin backbone, sugar, and acyl conjugates [66].

Improving water use efficiency in grapes is a main subject to sustain the cultivation of viticulture in semi-arid and arid areas. The target of vine cultivation is to secure high-quality fruit. This could be achieved in certain conditions that subject the plant to water stress that improves water use efficiency and obtains fruit with high quality rather than quantity.

Soil amendments stimulated root development and soil quality and improved the yield and quality of Thompson seedless grapevines. Furthermore, organic matter mineralization increased nutrient availability; this was demonstrated by an increase in enzymatic activities, especially β-glucoside, acid phosphatase, alkaline phosphatase, and humic and fulvic acid content [67]. Soil water balance is preserved through the growth stages of grapes by soil amendments such as hundzsoil. Hundzsoil improved the properties of berries due to increasing cation exchange capacity and mineral nutrients [31].

The addition of soil amendments such as hundzsoil is a way to conserve more water in the root zone and decrease the water stress effect [30]. One of the main advantages of using hundzsoil as a soil amendment is its ability to improve water use efficiency. By enhancing the soil’s structure and increasing water infiltration, hundzsoil helps to optimize the way plants absorb and utilize water from the soil. This results in better root development and stronger overall plant health, leading to increased crop yields and improved water use efficiency [33]. This explains the positive effect of numerous deficit irrigation interactions with hundzsoil on the investigated parameters such as shoot length, leaf area, bud fertility%, yield, cluster length and width, cluster weight, TSSs, TSS/acidity ratio, and IWUE.

The findings of this study suggest that spraying grapevines with proline could be a valuable strategy for improving water use efficiency in high-temperature and drought conditions. This could have significant implications for grape growers in regions where water scarcity is a major challenge, as it could potentially reduce the need for irrigation, saving valuable water resources while still maintaining crop yields. Furthermore, spraying grapevines with proline may also have positive impacts on the environment by reducing the amount of water needed for irrigation, which could help to conserve water resources and alleviate climate change effects.

Proline, an amino acid, is extremely useful to plants under a variety of stress circumstances [68]. Proline decreases the osmotic potential and attracts more water molecules into the cell, allowing it to maintain its turgor. Proline is characterized by high solubility in water and low molecular weight with no hazards to plants. It protects plants from abiotic stress by stabilizing proteins and protecting the membrane structure [69]. Proline can guard cells from damage by acting as both an osmotic agent and a radical scavenger. It provides a source of energy to actively separate cells as it supports justifiable growth under long-term stress [34]. Proline spray in this study was in those treatments that brought about an improvement in the quality characteristics of Crimson grapes under drought stress. The increase in shoot length and leaf area due to proline spray may be due to amino acids, which, as an organic nitrogenous compound, are the structural building blocks in the synthesis of proteins, which are created by a process in which ribosomes catalyze amino acid polymerization [70].

Plant proline concentration is enhanced during the ripening process [71]. It enhances photosynthesis by controlling the stomata’s opening and closing and preventing chlorophyll degradation, which balances CO₂ and water loss through the transpiration pathway and expands the leaf area. Proline also increases the epidermis thickness and influences the quantity of water lost through transpiration, maintaining the leaf water balance. Additionally, it helps in relieving the damage of drought stress, hence leading to increasing the TSSs of grapevines [72]. Phenylalanine and proline applications increased TSSs and anthocyanin in Crimson seedless grapes [22]. Proline spray improved yield and encouraged anthocyanin pigment accumulations in grapevines [39,73]. Moreover, treated Red Roumy grapevines with proline at 200 ppm increased SSC%, SSC/acid, total anthocyanin, total phenols, and total sugars, while this substance reduced acidity [39]. Amino acid application considerably improved soluble solids content, while the former reduced total acidity in berries as compared to untreated [74]. This illustrates the positive effects of deficit irrigation treatments, which interacted with proline, on some Crimson seedless parameters such as shoot length, weight of 100 berries, size of 100 berries, juice volume, berry length, berry diameter, clusters, berries number, TSS, acidity, TSS/acidity, and total anthocyanin. Proline spraying decreases the transpiration from plants in addition to improving yield production [39]. Both increase IWUE for grapevines.

In both successive seasons 2022 and 2023, there was no significant difference in yield production between 100% FC and 75% FC. In the second season, there was no significant difference between 75% FC and 60% FC. So, it is recommended to use 75% FC to save more water and increase IWUE. These results were in agreement with Weiler [75] who stated that more than 31% of water is saved without a significant negative effect on grape yield quantity and quality. Treatments with deficit irrigation level 60% FC and without hundzsoil or proline decreased the yield in both seasons. This indicated the importance of hundzsoil and proline in increasing the tolerance of grapevines to water reduction stress 60% FC.

5. Conclusions

Under the conditions of this study, treatments such as farm irrigation treatment 125% FC under 6 kg hundzsoil and proline spray, irrigation at 100% FC with only proline spray, and the irrigation level 75% FC with different doses of hundzsoil alongside proline spray had the highest positive effect on numerous growth parameters of Crimson seedless grapevines. On the other hand, both lower and higher irrigation levels (60% and 125% of the FC) without hundzsoil or proline spray negatively affected many growth parameters. Regarding the effect of deficit irrigation on the growth parameters of Crimson seedless grapevines, reducing the irrigation level up to 75% of the FC with all possible interactions with hundzsoil, once proline spray was applied, was the most effective in comparison with the other irrigation levels. There are ways to improve water use efficiency in grapevines, as achieved in our study. The addition of hundzsoil and spraying plants with proline conserves more water and could be a way to sustain viticulture in semi-arid and arid areas.