Effects of different spacing on tree growth and fruit quality of Chang Hong Fuji apple/SH6 during early stage after planting

Abstract:【Objective】The study aimed to investigate the effects of different density in row(0.75, 1.00 and 1.25 m) on the tree structure parameters, composition proportion of branches and fruit quality of Chang Hong Fuji apple/SH6 in order to provide a theoretical basis for the determination of suitable planting density in the apple orchard with SH6 dwarf rootstock.【Methods】The materials were Chang Hong Fuji/SH6 apple trees. The tree form was high-spindle-shape. The annual growth dynamic, structure composition and proportion of branches type, fruit yield and quality of the Chang Hong Fuji apple trees under the different plant spacing (0.75, 1.00 and 1.25 m × 4.0 m), were investigated from the second to the sixth years after planting. The trees were divided into different canopies (＜1.00 m, 1.00-2.00 m, ＞2.00-3.00 m and ≥ 3.00 m) from the bottom to the top of the trees. The yield and proportion of fruits in different canopy were investigated, and the effects of plant spacing on the spatial distribution of fruit yield were analyzed.【Results】From 2016 to 2020, the tree height, length and number of main branches showed an increasing trend. The number of main branches per hectare was decreased with the increase of plant spacing. The annual growth of the tree height could be affected by the plant spacing, but the total growth of tree height was not affected. With the increase of plant spacing, the annual growth of the tree height showed an increasing trend in 2016 and 2017, the annual growth of the tree height showed a decreasing trend in 2018 and 2019. With the increase of plant spacing, the canopy width (east-west, south-north), trunk diameter of the variety and rootstock, coverage rate of the canopy showed an increasing trend; The annual growth rate of coverage rate was increased rapidly from 2016 to 2017. When the planting density was 1.25 m×4.00 m, the branch length was the longest, which was significantly longer than those of the other treatments. With the increase of plant spacing, the number of the total branches showed a descending trend, the number of the total branches showed a gentle growth trend from 2016 to 2018 and a rapid growth trend from 2019 to 2020, the proportion of spur branches increased significantly from 2019 to 2020. The composition proportion of different branches in different canopy heights was analyzed, with the increase of plant spacing, the concentrated area with the highest proportion of spur shoots (＜5 cm) in the canopy showed a downward trend, the concentrated areas with the long shoots (30-＜60 cm) and medium shoots (15-＜30 cm) were on the top and bottom of the tree, respectively. The concentrated areas with the highest proportion of spur shoots (＜5 cm) in the canopy were in 1.00-2.00 m, ＞2.00-3.00 m and over 3.00 m according to the planting density (0.75 m × 4.00 m, 1.00 m × 4.00 m and 1.25 m × 4.00 m). The fruit yield of Chang Hong Fuji showed a decreasing trend with the increase of plant spacing. The fruit mass, soluble solids, solid acid ratio, color difference value L and a showed an increasing trend, while fruit firmness and titratable acid content showed a decreasing trend with the increase of plant spacing. Therefore, as the plant spacing increased, the quality, soluble solids, solid acid ratio and color of the fruits could be significantly improved, while the concentrated areas of fruit yield showed a downward trend. The regions with the highest proportion of fruit yield in the canopy were in over 3.00 m, ＞2.00-3.00 m and 1.00-2.00 m respectively, according to the different density.【Conclusion】The spacing (1.00-1.25) m × 4.00 m was more suitable for Chang Hong Fuji apple /SH6 in the high-spindle-shape during early stage after planting. With this spacing, the proportion of different branches of the trees was more reasonable, the internal and external quality of the fruits were better, and the fruit yield was higher.