Grapes Vitis vinifera is belonging to the Vitaceae family and are an important fruit crop globally and in the Arab world. They are among the most prominent fruit crops in terms of cultivation and production. Grape cultivation is widespread in warm and semi-arid regions due to its adaptability to varying climatic conditions. Grapes are a crop of strategic importance because of their versatility, whether for fresh consumption or processing into various products such as raisins, juices and others (Amorim et al., 2020). Polyols are metabolic products of photosynthesis in many plants. They are carbohydrates called “alcoholic” because of their chemical structure, which includes a hydroxyl group (-OH). These compounds are characterized by their high mobility and rapid translocation between plant organs via phloem tissues, effectively contributing to the distribution of energy and nutrients within the plant (Li et al., 2023). Recent advances in understanding the mechanisms of polyol translocation and their role in micronutrient transport have contributed to improving the effectiveness of foliar fertilization and increasing the uptake of essential nutrients for plant growth and crop quality (Guirao et al., 2024).
       
Sulfur is an essential nutrient for plants. It is a component of sulfur-containing amino acids such as methionine and cysteine and participates in the synthesis of proteins and enzymes. Its role in enhancing the plant’s ability to cope with varying environmental conditions is crucial. In grapes, sulfur plays a significant role in promoting growth and improving fruit quality, especially when added as zinc sulfate as a soil fertilizer. This provides the plant with both sulfur and zinc, enhancing physiological activity, increasing the efficiency of photosynthesis and stimulating chlorophyll formation. Zinc is the fourth most important mineral element in plant nutrition after nitrogen, phosphorus and potassium. It is a slow-moving element within the plant, yet it is essential for growth and the plant life cycle. Zinc ions are involved in the synthesis of several vital enzymes that play central roles in metabolic processes, such as catalyzing oxidation-reduction reactions and synthesizing plant auxins like indole-3-acetic acid (IAA), which is one of the most important hormones regulating vegetative growth and photosynthesis (Singh et al., 2024). Therefore, the aim of study was to apply foliar application of silicon oxide, sorbitol and zinc sulfate on vegetative growth characteristics of Halawani grape cultivar Vitis vinifera.

Experimental site
 
The experiment was conducted during the 2023-2024 growing season in a private orchard in Al-Hadid village, near the Al-Khalis Grand Project in Diyala Province. The 10-year-old Halwani grape varieties have been selected. The aim was to study the effect of spray levels of silicon oxide, sorbitol and zinc sulfate on grape growth and yield. Eighty-one plants, selected for their similar size and vigor, were trained on overhead wire trellises. Random soil samples were taken from several locations before the experiment began, at depths of 0-30 cm and 30-60 cm and analyzed at the soil laboratory of the Diyala Agriculture Directorate.
 
Silicon oxide (SiO₂)
 
Silicon oxide SiO₂ (50% Si) (Thomas Baker, India) was used at three levels (0, 3 and 6 mg/L^-1). It was sprayed on the foliage of the trees until the leaves were completely saturated. Three spray treatments were carried out, starting in April and continuing until June. The first spray coincided with the full fruit set stage, the second during the rapid berry growth and seed hardening stage and the third at the beginning of the veraison stage. To increase absorption efficiency, the surfactant Tween-20 was used at a concentration of 0.1%. All spraying operations were carried out in the early morning hours, one day after irrigating the plants (Bassiony et al., 2017).
 
Sorbitol (C₆H₁₄O₆)
 
Sorbitol (C₆H₁₄O₆) (Lobachemie, India) was used at three concentrations (0, 50 and 100 mg/L^-1) and sprayed onto the foliage starting from the full fruit set stage with three consecutive applications, 20 days apart, during the period from April to June. This covered the critical stages of fruit growth and development up to the beginning of the coloring stage. The surfactant Tween-20 was used at a concentration of 0.1% to increase absorption efficiency (Guirao et al., 2024).
 
Zinc sulfate (ZnSO₄•H₂O)
 
Zinc sulfate (ZnSO₄•H₂O) with 99% purity (LOBA Chemie Pvt. Ltd., India) was added at three levels (0, 75, 150 g. plant^-1). The substance was added to the soil around the perimeter of the tree’s drip line one week after full flowering was completed, to ensure efficient absorption and increased availability of the element during the fruit set period and the development of vegetative and fruit growth (Armachius et al., 2022; Alloway, 2008).
 
Growth characteristics
 
Leaf area
 
Single leaf area (cm²) was estimated using the leaf-disc method. This involved taking the average weight of (40) fully grown leaves from fruiting canes, then cutting discs with a diameter of (2 cm²) after cleaning the leaves. The leaf area per leaf was calculated using the following equation:

 
Chlorophyll content (mg/100 g^-1 soft weight)
 
Chlorophyll content in leaves collected from leaf 5 to 6 of the growing tip was estimated according to the method Goodwin (1976) by crushing 0.2 g of leaves placed in a labeled glass bottle and adding 20 mL of 85% acetone.

 
₆₆₃A₆₄₅, A = Absorbance at wavelengths of 645 and 663 nm.
V = Final volume of extract (liters).
W = Weight of the fresh sample (g).
       
Light absorption at wavelengths of 663 and 645 nm respectively was measured using a spectrophotometer. The total chlorophyll content (mg L^-1) was calculated and then converted from mg L^-1 to mg 100 g^-1.
 
Nitrogen content in leaves (%)
 
Nitrogen was estimated using the Kjeldahl method according to Nelson and Sommers (1980).
 
Potassium content of leaves (%)
 
Potassium was estimated using a flame photometer as reported in (Tandon, 1995).
 
Boron content in leaves (mg/kg^-1 dry matter)
 
Boron was estimated using the curcumin method (Singh et al., 2024).
 
Proline content of leaves (µg.g^-1)
 
The method of was followed as 0.5 g of leaves were taken per experimental unit from each treatment and crushed in a ceramic mortar with 5 mL of 3% sulfosalicylic acid until the mixture was homogenized. The precipitate was then separated from the filtrate by centrifugation at 2500 rpm for five minutes. Two mL of the filtrate were taken and two mL of glacial acetic acid and two mL of acidic ninhydrin solution (prepared by dissolving 1.25 g ninhydrin in 30 mL of concentrated glacial acetic acid and 20 mL of 30% phosphoric acid) were added. The tube was gently shaken and placed in a boiling water bath for 30 minutes to complete the reaction.
       
It was then allowed to cool to laboratory temperature, after which 5 mL of concentrated toluene (98%) was added for separation. The proline was removed from the mixture and the tubes were vigorously shaken in a vortex mixer at full speed for 30 seconds. The tubes were then left to stand for five minutes. The toluene layer was removed using a pipette and its optical absorption was recorded using a spectrophotometer at a wavelength of 520 nm. The proline content was then estimated using the following equation:

Chlorophyll content (mg/g^-1 fresh weight)
 
The results indicated that treatments with silicon oxide, sorbitol and zinc sulfate, individually and in combination, significantly affected leaf chlorophyll content (mg/g^-1). A silicon oxide concentration of 6 mg/L^-1 resulted in the highest average content of 32.51 mg/g^-1, while a concentration of 3 mg/L^-1 resulted in the lowest average content of 31.13 mg/g^-1. the results showed that a concentration of 100 mg/L^-1 significantly increased chlorophyll content to 33.16 mg/g^-1, while a concentration of 50 mg/L^-1 resulted in the lowest average content of 30.71 mg/g^-1.
       
The triple interaction between silicon oxide, sorbitol and zinc sulfate, the interaction A3B1S3 (6) mg L^-1 SiO₂  (0) × mg L^-1 sorbitol × 150 mg L^-1 ZnSO₄ showed the highest chlorophyll content of 34.6511 mg g^-1, while the interaction (3) A2B2S1 mg L^-1 (50) × SiO₂  mg L^-1 sorbitol × (0) g L^-1 ZnSO₄ gave the lowest content of 27.2856 mg g^-1 (Table 1).


 
Nitrogen content of leaf (%)
 
The treatments with silicon oxide, sorbitol and zinc sulfate significantly affected the nitrogen content of leaf petioles. The concentration of 6 mg L^-1 gave the highest average silicon content of 2.144 mg g^-1, significantly surpassing the other concentrations, while the lowest value was obtained in the control treatment, with an average of 2.098 mg g^-1 (Table 2).


       
Sorbitol, at a concentration of 50 mg/L, achieved the highest mean (2.180%) and was significantly superior to the no-spray treatment, which yielded the lowest mean (2.032%). Zinc sulfate also significantly outperformed the other treatments, with a concentration of 75 g/L yielding the highest mean (2.29%), while the no-spray zinc sulfate treatment yielded the lowest mean (1.915%). The results of the three-way interaction between the studied factors showed that the treatment of spraying with silicon oxide, sorbitol and zinc had the highest nitrogen content at concentrations of 6 mg/L silicon ×  0 mg/L sorbitol ×  75 g/L zinc (2.773%), which was not significantly different from the 6 mg/L treatment. L^-1 silicon ×  100 mg L^-1 sorbitol ×  150 g L^-1 zinc) gave 2.713%, while the lowest value was in the no-spray treatment, which amounted to 1.663% (Table 2).
 
Potassium content of leaf (%)
 
The results show that treatments with silicon oxide, sorbitol and zinc sulfate affected the potassium content of leaf petioles. The silicon oxide spray treatment at a concentration of 6 mg L^-1 recorded the highest average value of 1.701, while the lowest value was at a concentration of 3 mg L^-1, reaching 1.469. The control treatment did not differ from this, with an average value of 1.529. As for sorbitol, the concentration of 100 mg L^-1 showed the highest average value of 1.640 mg g^-1, while the lowest value was in the control treatment, reaching 1.4996 mg g^-1 (Table 3).


       
The results also showed that zinc sulfate at a concentration of 75 g L^-1 gave the highest average potassium content of 1.669%, while the lowest value was recorded for the distilled water spray treatment at 1.462% (Table 3).
 
Boron content in leaf (mg/kg^-1 dry matter)
 
The treatments with silicon oxide, sorbitol and zinc sulfate significantly affected the boron content of the sap. Spraying with silicon oxide at a concentration of 6 mg/L^-1 yielded the highest mean concentration of 33.30, while the lowest value was recorded in the control treatment at 29.95 mg/kg^-1. Regarding the effect of sorbitol, a concentration of 50 mg/L^-1 produced the highest mean concentration of 32.29, while the lowest value was recorded in the no-spray treatment at 30.76. The results also showed that spraying with zinc sulfate at a concentration of 150 g/L^-1 increased the boron content of the juice, with an average of 32.08. This effect was not significantly different at a concentration of 75 g/L^-1, while the lowest value was recorded in the control treatment at 30.87 (Table 4).


       
The results of the triple interaction between silicon oxide, sorbitol and zinc sulfate showed a significant effect. Spraying with silicon oxide at a concentration of 6 mg/L, sorbitol at a concentration of 50 mg/L and zinc sulfate at a concentration of 150 g/L resulted in the highest average boron content of the juice, reaching 36.83. Conversely, the lowest value of 20.88 was observed in the no-supplement treatment (no silicon oxide, sorbitol, or zinc sulfate) (Table 4).
 
Proline content in leaves
 
The treatments with silicon oxide, sorbitol and zinc sulfate affected the proline content. The lowest value was recorded with silicon oxide spraying at a concentration of 6 mg/L, with an average of 0.877 µg/g dry weight, while the highest value was 0.997 µg/g dry weight at a concentration of 3 mg/L. the effect of sorbitol on proline content, a concentration of 50 mg/L resulted in a decrease in proline content to an average of 0.905 µg/g dry weight, compared to the no-spray treatment which resulted in 0.978 µg/g dry weight. A concentration of 100 mg/L yielded a similar average of 0.920 µg/g dry weight (Table 5).


       
The treatments with silicon significantly improved the physiological characteristics of plants. This improvement can be attributed to increased leaf area, dry matter accumulation and total leaf chlorophyll content, as well as increased nitrogen, potassium, boron. This demonstrates its role in enhancing the efficiency of photosynthesis, promoting cell elongation and improving cell wall elasticity. Furthermore, silicon has been shown to strengthen cell wall structure and improve nutrient absorption, thus increasing plant growth (Xu et al., 2023; Bhangare et al., 2020).
       
The decrease in leaf proline content when sprayed with silicon is due to the reduction of water loss through transpiration. Silicon improves the activity of peroxidase and catalase enzymes, thus reducing proline accumulation (Marschner, 2012 and Kavya et al., 2021). The significant increase in physiological yield characteristics resulting from silicon spraying is attributed to its effective role in improving vegetative growth efficiency. This led to an increase in leaf area and dry matter accumulation, as well as higher total chlorophyll content in leaves, nitrogen, potassium, boron.
       
The increase in silicon spraying results in improved vegetative growth efficiency. These results can be interpreted as indicating that silicon spraying improved light absorption efficiency by increasing cell membrane permeability and reducing the effects of environmental stresses. This, in turn, led to increased photosynthetic efficiency and the production of secondary metabolites. These results are consistent with those reported by Laane (2018) and Medan et al., (2026).

The study concludes that sorbitol at a concentration of 100 mg/L resulted in higher total leaf chlorophyll content and higher petiole potassium and boron content, while reducing leaf proline content. Treatment with zinc sulfate at a concentration of 75 g/L resulted in higher total leaf chlorophyll content and higher petiole nitrogen, potassium and boron content, while reducing leaf proline content.

The authors declare that no conflict of Interest.