Effects of bearing-branch management on fruit quality of Shine Muscat grape

Abstract:【Objective】Bearing-branch management is a key cultivation strategy to increase fruit quality through regulating the balance between nutritional and reproductive development by improving the ventilation and lighting conditions. However, there are no established guidelines for bearing- branch management of Shine Muscat grape. In this work, the impact of various branch management techniques on the fruit quality of Shine Muscat grape was investigated.【Methods】There were six treatments, including CK group: 7-8 leaves were retained above the fruit ears, the leaves at the top of the bearing branch were repeatedly taken off and 2 leaves were left on the lateral shoot after pinching; J0: 7- 8 leaves were retained above the fruit ears with repeatedly pinching of bearing branch, and no leaves was left on the lateral shoot; J1: 7-8 leaves were retained above the fruit ears, the leaves on the top of the bearing branch were repeatedly pinched and 1 leaf was left on the lateral shoot; X0: no leaves were left on the lateral shoot with no pinching of bearing branch; X1: no pinching of bearing branch and 1 leaf was left on the lateral shoot; X2: no pinching of bearing branch and 2 leaves was left on the lateral shoot. The fruit weight, vertical diameter, transverse diameter, soluble solids, soluble sugar content, titratable acid, ratio of soluble solids/acid and aroma components of the berries with different treatments were measured. 3 parallel trees were selected for each treatment.【Results】The fruit transverse diame-ter, soluble solids content, soluble sugar content and ratio of soluble solids/acid could all be dramatically increased by the treatment, that is, 7-8 leaves were retained above the fruit ears, the leaves on the top of the bearing branch (J1) were repeatedly pinched and 1 leaf was left on the lateral shoot. The bearing branches had higher fruit weights, transverse diameter, and ratio of soluble solids/acid than the bearing branches with long-release treatment. It was possible that bearing branches pinching facilitated the concentration of the photosynthetic products of the leaves, while the bearing branches with long- release treatment had two growth centers, and the competition for nutrients weakened fruit growth. Regardless of whether the bearing branches were plucked or long-released, the treatment of 2 leaves on the lateral shoots had the lowest fruit weight, transverse diameter, and soluble sugar content, whereas the treatment with 1 leaf on the lateral shoots had the greatest. The content of hexanal and 2-hexenal was the highest among the aldehydes, and the content of hexanol was the highest among the alcohols, while the content of ketones, esters and terpenes were less, indicating that the aroma substances in each treatment mainly consisted of aldehydes and alcohols. The J0 group had 9 different forms of aldehydes, with 2- hexenal and N-hexenal being the two most prevalent varieties. The total ester content of J0, J1, X1 and X2 treatments were much higher than that of the CK and X0 groups. The X0 group treatment had the greatest overall ketone content. The J0 treatment had dominances in the kinds and overall content of fragrance compounds. The six treatments were separated into two clusters according to cluster analysis: one for J0, J1, X1 and X2 and another for CK and X0. The J0 treatment had higher content of alcohols and terpenoids such as linalool, (+) -α-terpineol and trans-2-hexenol than the other treatments. The X1 group treatment had higher aldehydes including hexanal, 2-hexenal than the other treatments. The X2 group treatment had more esters and N-hexenol than the other treatments. The J1 and CK were ranged at number four, followed by the X0 treatment, which had the lowest content of chemicals. The effects of each resulting branch treatment on aroma components were J0＞X1＞X2＞J1, CK＞X0 in order【Conclusion】The treatments of J1 and J0 could maximize the fruit weight, transverse diameter and soluble sugar content. The types and total contents of aroma substances of J0 group were the highest, the contents of alcohols and terpenes of J0 group were also higher than those of the other treatments, and the aroma components of Shine Muscat grape were improved most significantly. In conclusion, 7-8 leaves retained above the fruit ears with repeatedly pinching of bearing branch, and no leaves left on the lateral shoots could be regarded as the most effective method for bearing branches management in the summer to improve the comprehensive quality under the experimental conditions.