Foliar application of alanine, glutamine and tryptophan improves the growth parameters and bunch quality of Early Sweet grapevines in clay soils under surface-irrigated system

The grapevine (Vitis vinifera L.) is one of the most profitable fruit crops globally. 'Early Sweet' stands out as one of the earliest grape varieties to be commercially marketed. Three amino acids (alanine, glutamine, and tryptophan) were applied as foliar sprays at concentrations of 100, 200, and 300 ppm, at three key growth stages: the start of growth, full bloom, and version. This study was carried out over two consecutive seasons (2021 and 2022) in Mansoura City, Dakahlia Governorate, Egypt (31° 26' 45.6" E, 31° 07' 19.2" N). The experiment was conducted on 6-year-old Early Sweet grapevines grown under surface irrigation in clay soil. Vines trained a quadrilateral cordon trellis system with supported by Spanish baron system. The results indicated that spraying the vines with amino acids (alanine, glutamine, and tryptophan) significantly enhanced yield per vine, bunch weight, berry weight, soluble solids content, total sugars, and carotenoid content, while reducing the incidence of shot berries and total acidity in the berries. Additionally, the treatments improved internode length and thickness, pruning wood weight, ripening wood, and total carbohydrates in canes, as well as shoot length, number of leaves per shoot, and leaf area. There were also increases in the percentages of nitrogen (N), phosphorus (P), potassium (K), and total chlorophyll in the leaves compared to the control group in both seasons. All measured parameters showed a gradual improvement with increasing concentrations of amino acids. Overall, these amino acids could be recommended for application in Early Sweet vineyards.