Effect of branch drooping treatment on photosynthetic characteristics and fruit quality in Shine Muscat grapevines with WH-shaped tree shape

Abstract:【Objective】In protected cultivation of grape, training and pruning are essential practices. Canes of grapevines are of high plasticity and can form various shapes through these practices. A reasonable canopy shape is essential for the balance between vegetative and reproductive growth of vines and for yield and quality formation. Modern agriculture has a higher requirement for canopy shape, which needs to be ornamental and diversified as well as productive, high-quality and convenient in man-agement. The WH shape is a high-yield, high-space-utilization vine shape under scaffolding cultivation. However, due to the space constraints, the WH shape is disorganized and difficult to management dur-ing grape production. In this paper, we study the branch drooping treatment at different distances from the cordon to identify the best branch drooping treatment that enables labor- saving management and maximizes fruit quality.【Methods】Six- year- old WH- shaped Shine Muscat grapevines grown under rain shelter were used as materials. The grapevines were planted at an 8.0 m × 8.0 m spacing. Each branch was allowed to bear two clusters of grapes, and the fruit was thinned in a standardized manner with standardized fertilization, watering and pest control management. The cordon of Shine Muscat grapevines with similar growth states were selected for treatments. The shoot growth rate, tendril growth rate, leaf photosynthetic indexes such as photosynthetic rate, stomatal conductance, transpiration rate and intercellular carbon dioxide concentration, leaf chlorophyll content, and fruit quality pa-rameters at maturity such as fruit weight, longitudinal and transverse diameter, soluble solids and color were measured.【Results】The branches of the horizontal growth treatment (control treatment) had ex-cessive vegetative growth with faster growth of the secondary tendrils and greater photosynthetic rate but with poorer fruit quality, smaller fruit weight compared with the branching drooping treatment. Compared with the control, the treatment of pulling down branches 30 cm from the cordon reduced the growth of the secondary tendrils by 50%-60% and chlorophyll content of the leaves by 12%. The foliage photosynthetic rate in this treatment decreased greatly compared with the control, and maintained lower than the other treatment on the same day; stomatal conductance was significantly decreased, while the intercellular CO2 concentration and the transpiration rate slightly decreased. Among all the treatments, the longitudinal and transverse fruit diameters and single fruit weight in branch dropping at 30 cm were the largest, with soluble solid content increased and acid fixation decreased at the same time. The fruit skin coloration was more uniform than the other treatments. However, in this treatment, the distance of branch drooping from the cordon was small, which was not convenient for management. The treatment of pulling down the branch at 60 cm from the cordon also had a significant inhibitory effect on the growth of secondary tendrils, which was reduced by 40%-50% compared with the control, and the chlorophyll content in the leaves and photosynthetic rate were also reduced. The treatment of pulling down the branch at 90 cm from the cordon also significantly inhibited the growth of secondary tips and tendrils by 18%-30%, which led to a more beautiful tree shape, which enables labor- saving management. The treatment slight reduced chlorophyll content, stomatal conductance, intercellular carbon dioxide concentration, and transpiration rate of leaves, but net photosynthetic rate was high and above 13 μmol · m- 2 ·s - 1 and fruit quality indexes such as longitudinal and transverse diameter, soluble solids content, fruit weight, and coloration was improved. The treatment at 120 cm from the cordon did not cause significant inhibition of the growth of the secondary tendrils; chlorophyll content and photosynthetic rate did not change much; stomatal conductance decreased; fruit quality was lower with decreased soluble solids content.【Conclusion】The selection of the modified WH shaped tree with branch drooping at 90 cm from the cordon improved fruit quality and photosynthetic capacity of Shine Muscat grapevines, without significant decrease in photosynthetic rate and on the vegetative growth. The tree shape formed from the treatment was aesthetically pleasing and easy to manage.