PRINCIPLES OF TRAINING AND PRUNING TRADITIONAL OPEN-CENTER APPLE TREES IN JAPAN
Conventional apple orchards in Japan are low density (150 to 200 trees/ha) with trees worked on Marubakaido (Malus prunifolia), semi-standard rootstock. Trees are trained by a traditional system to a specific open-center form with flat canopy of moderate height. The number and length of scaffold limbs are strictly restricted, and lateral branches are developed on near-horizontal limbs kept well apart from the trunk. This framework structure facilitates the development of a flat canopy and the arrangement of lateral branches with uniform vigor throughout the canopy. The canopy height is largely determined by potential tree vigor, which is closely related to environmental conditions. This relationship explains the differences in canopy height among areas under different environmental conditions. Young trees are trained as the central leader tree for 6 to 10 years. The timing of removing the central leader is also influenced by the potential tree vigor and brings about a great diversity of mature tree shape.
Kikuchi, T. and Shiozaki, Y. (1992). PRINCIPLES OF TRAINING AND PRUNING TRADITIONAL OPEN-CENTER APPLE TREES IN JAPAN. Acta Hortic. 322, 37-44