Study on high -density planting of different dwarf inter rootstock combinations in apple

In order to determine suitable planting density for a wide -line close planting cultivation pattern of different dwarf inter-rootstock of apples, three different dwarf inter-rootstock combinations planted in 2010 have been chosen as experiment materials, namely, short-shoot cultivar and dwarfing rootstock `Tianhong 2'/ SH40/Malus robusta, strong dwarfing `Yanfu 3'/M9/M. robusta and weak dwarfing `Yanfu 3'/M26/M. robusta. From 2013-2015 (the fourth, fifth, and sixth year after planting), the influence of different planting densities (0.75, 1.0, 1.25 and 1.5x4.0 m) on tree growth, orchard structure, the function of leaves, yield, and quality was studied continuously, and the results were as follows. Planting density has no significant impact on tree height, trunk height, and trunk girth. The conjoining rate in plants with row spacing of 0.75 and 1.0 m is significantly higher than the other two treatments. Short shoot rate in the treatment of giving 0.75 and 1.0 m row spacing is significantly higher than the treatment of 1.5 m spacing in the rows, but the proportion of developing branches in plants with row spacing of 1.5 m is significantly higher than other treatments. Orchard coverage decreases with the increase in planting density for SH40 combination. Plants with row spacing of 0.75 and 1.0 m have a higher leaf net photosynthetic rate, and for M9 and M26 combinations, plants with row spacing of 1.0 and 1.25 m have the highest leaf net photosynthetic rate. As for yield, the highest is for the plants with a row spacing of 0.75 m, followed by the plants with a row spacing of 1.0 m, but yield per plant of plants with row spacing of 1.5 and 1.25 m is higher than that of 0.75 and 1.0 m in the sixth year. As for soluble solid contents (SSC), fruit shape index, and weight of single fruit, the highest in the SH40 combination are the plants with row spacing of 0.75 and 1.0 m, and the highest in M9 and M26 combinations are those with row spacing of 1.0 and 1.25 m. As for fruit hardness, plants with row spacing of 1.0 m (9.54 and 9.46 kg cm(-2)) are the hardest in SH40 and M26 combinations, and plants with row spacing of 1.0 and 1.25 m (9.52 and 9.32 kg cm(-2)) are the hardest in M9 combination. There is no significant difference in brightness, cleaning index, and colouring index for all treatments for the three combinations. It is comprehensively analysed that based on the studies on apple trees with dwarf inter -rootstock in the fourth to sixth year, the `Tianhong 2'/SH40/M. robusta combination is suitable for 0.75 or 1.0x4.0 m, while the 'Yanfu 3'/M9 and M26/M. robusta combinations are suitable for 1.0 or 1.25x4.0 m.