Effects of Dwarfing Interstock Length on the Growth and Fruit of Apple Tree

There is no report on the effect of the length of Jizhen 2 interstock on the growth and fruit quality of Tianhong 2 apple trees, which are usually grown in Baoding, Hebei Province, China. We surveyed the tree size, branch types, fruit set, fruit quality and root parameters of 3-5-year-old 'Tianhong 2/Jizhen 2/Malus x robusta Rehder' apple trees, to study the effects of dwarfing interstock length on the growth of the tree's aboveground parts and roots, as well as fruit yield and quality. The tree height and the stem girths of the interstock and scion decreased as interstock length increased, and the dwarfing degree of the apple trees gradually increased. Trees with an interstock length of 30 cm had the fewest long branches, the most short branches, and the greatest proportion of short branches. An interstock length of 30 cm provided the highest fruit-set rate, the highest yield per tree and per unit cross-sectional area, the highest single fruit weight, the highest soluble: acid ratio, the highest color brightness (L*), and better red skin coloration (higher a*) of the fruit skin. The root length density, root surface area density, and root volume density exhibited two growth peaks in a year, during the slow growth period when spring and autumn shoots are stopped. Root length density, root surface area density, and root volume density decreased with interstock length. Root death peaked during the growth peak period of the autumn shoots, and root length density of dead roots and root turnover frequencyincreased with the interstock length. A 30 cm length was the most suitable for the Tianhong 2 apple trees when the Jizhen 2 was used as the interstock.