Effect of traction of branches on the growth of Jinyan kiwifruit

Abstract:【Objective】In recent years, kiwifruit industry has been developing rapidly. Although kiwi-fruit planting area and output in China rank the first in the world, the industry is still inferior to that in developed countries in terms of fruit productivity, fruit qualities, and cultivation levels. In order to im-prove the yield, quality, cultivation pattern and international competitiveness of Chinese kiwifruit, the effects of branch- traction on the growth of Jinyan kiwifruit were studied.【Methods】Current- year branches in 10-year-old Jinyan kiwifruit trees were used as test materials for traction treatment carried out in 2018 to 2019. The effects of branch traction on changes in the lengths and diameters of annual branches during growing periods, budding and flower bud rates of shoots with different diameters were recorded; photosynthetic gas exchange parameters and contents of photosynthetic pigments were ana-lyzed in traction layers, fruiting layers and control groups; fruit qualities, endogenous hormone con-tents, and carbon to nitrogen ratio were determined for buds on annual branches with different diameters.【Results】Compared with the control, the traction treatment significantly increased the growth of current year branches by 24.4% during the growing period and the proportion of medium diameter branches (6-10 mm diameter) increased by 106.5%, and the growth of the thickest branches (>10 mm diameter) reduced, resulting in more uniform new branches in terms of stem thickness. Besides, the pho-tosynthetic gas exchange parameters of leaves in the traction layer increased significantly, but there was no significant difference in the leaves of the fruit layer. In addition, the chlorophyll a/b ratio of the leaves in the fruiting layer was significantly lower than that of CK. Furthermore, the number of buds on fruit-bearing base branches of the treated trees increased significantly, reaching 1.57 times of CK. Al-though there were no significant differences in external and internal fruit qualities of kiwifruit, the yield per plant of the treated trees increased significantly, reaching 102.6 kg, which was 2.03 times higher than that of CK. With respect to shoots, the content of zeatin (ZR) in aboveground part showed an over-all downward trend; the content of auxin (IAA) and abscisic acid (ABA) showed an upward trend; and the content of gibberellin (GA3) decreased first and then increased. ZR/GA3, ZR/ABA, and ABA/GA3 ra-tios all demonstrated a downward trend first and then an upward trend. ABA/IAA ratio tended to de-crease and then increase, while IAA/ZR ratio tended to increase all the time. The soluble sugar content,carbon content and soluble protein showed an overall trend of increasing and then decreasing, while the starch content showed a decreasing trend. Compared with the buds on branches larger than 10 mm in di-ameters, the ZR contents in the buds of 6-8 mm and 8-10 mm thick branches were higher while GA3,IAA, and ABA contents were lower than those in branches larger than 10 mm in diameter. ZR/GA3, ZR/ABA, and ABA/IAA ratios in buds in 6-8 mm and 8-10 mm thick branches were overall significantly higher and IAA/ZR significantly lower than those in branches larger than 10 mm diameter. ABA/GA3 ratio in buds in branches 8-10 mm in diameter was significantly higher than those in branches larger than 10 mm diameter. The soluble sugar content and carbon content in 6-10 mm shoots were generally signif-icantly higher than in branches larger than 10 mm diameter. Furthermore, significant differences were found in percentages of sprouting buds and floral buds among branches with different diameters with the highest percentage found in branches 8-10 mm in diameter, followed by 6-8 mm branches, and the lowest percentage was seen in branches larger than 10 mm.【Conclusion】The effects of branch-traction treatment on the growth of kiwifruit were multifaceted. In one hand, the branch-traction treatment pro-motes the growth of current year branches, which is beneficial to flower bud differentiation thus signifi-cantly increases fruit yield; in the other hand, the branch-traction treatment improves the photosynthetic capacity of kiwifruit leaves, which is beneficial to fruit quality. In conclusion, branch-traction treatment is an optimal cultivation pattern for Jinyan kiwifruit.