Impact of appropriate machine-based contour pruning on the tree structure and fruit quality of jujube trees

【Objective】Junzao jujube is an important economic crop in the arid northwest region, and its yield and quality is significantly influenced by tree management techniques. Traditional manual pruning faces practical issues such as low efficiency and high cost. Therefore, this study aims to explore the regulatory effects of mechanized contour pruning on the tree structure and fruit quality of Junzao jujube, in order to address the limitations of current pruning techniques.【Methods】Using 7-year-old Junzao jujube trees as experimental materials, six different mechanized pruning treatments with varying tree heights and crown widths were set up, along with a manual pruning control (CK). Phenological period, tree structure, chlorophyll content, light interception area, yield, and fruit quality indicators were measured. Variance analysis and principal component analysis were employed and combined to explore the regulatory effects of mechanized contour pruning. Throughout the growth cycle of jujube trees, continuous and detailed observations were carried out on key growth stages such as the budding period, ini-tial flowering period, full flowering period, young fruit period, white ripening period, semi-red period, full-red period, and maturity period. For the tree structure, the number of non-fruiting jujube branches, fruiting jujube branches, lignified jujube branches, non-fruiting jujube stocks, and fruiting jujube stocks were counted. In addition, for the whole tree, parameters such as the number of one- year- old jujube heads, the number of perennial jujube heads, crown width, tree height, Leaf Area Index (LAI), chlorophyll a, chlorophyll b, and light interception were measured. Laser rangefinders, tape measures, and professional leaf area measuring instruments were used to ensure the accuracy of the data. The yield of jujube trees was determined by measuring the single - plant yield of Jun jujubes, the yield of commercial jujubes, and the yield of defective jujubes. Each jujube tree was carefully harvested, and the fruits were classified and weighed to obtain accurate yield data. The external quality of fruits was evaluated by measuring parameters such as the commercial rate, single-fruit weight, fresh-fruit transverse and longitudinal diameters, fruit shape index, and fruit moisture content. Precision balances, vernier and calipers were used for measurement. For the internal quality of fruits, parameters such as soluble solids, Vc, soluble sugars, titratable acids, protein content, total flavonoids, and total phenols were analyzed. High-performance liquid chromatography (HPLC), and spectrophotometry were employed.【Results】Pruning can delay the phenological period, and the greater the pruning intensity, the more significant the delay effect. T2 had a germination period 7 days later and a maturity period 5 days later than the control group; T5 and T6 showed little difference with the control group. Pruning can optimize the light distribution in the canopy, with T6 having the highest light interception amount, reaching 94 468.87 μmol·m-2 ·s -1 , while T1 having the lowest; moreover, pruning can promote the growth of one-year-old jujube shoots, regulating canopy width and tree height. T1 and T2 significantly improved fruit quality, with soluble solids reaching 35.45% and total phenols reaching 14.00 mg·g-1 ; T4 performed the best, with a single fruit weight of 37.3 g, a commercial rate of 74.7%, and balanced contents of soluble sugars and vitamin C; T6 had the highest yield per plant, but the single fruit weight and sugar content were lower.【Conclusion】Mechanized contour pruning exerts a synergistic regulatory effect on both the tree structure and fruit quality of Junzao jujube. Specifically, among them, under treatment T4, light interception efficiency increased by 2.06% compared to the control (CK); average single-fruit weight increased by 30.4%; and the contents of soluble solids, Vitamin C, soluble sugars, titratable acids, total phenols, and flavonoids increased by 13.9%, 31.8%, 28.5%, 10.95%, 23.3%, and 21.7%, respectively, relative to the control. This can be used as the preferred scheme for achieving mechanized management, quality improvement, and efficiency enhancement in Xinjiang jujube orchards.