Pruning is a dwarfing process and the degree of dwarfing is related to the severity of pruning. Light pruning may produce no recognized dwarfing response; the response to severe pruning may be easily seen and extend for several years. Pruning disturbs the balance between root and shoot growth. Root growth is slowed or stops as assimilates and growth hormones are directed to renewed shoot growth. Reduced root growth means less water and nutrient absorption. This furthers the stress and results in a dwarfing response by the tree. Dormant pruning disrupts apical dominance by removal of the auxins contained in the apical bud that prevent growth of the lower lateral buds. It is known that auxins are important in root growth. Loss of auxins through pruning affects root growth, which affects cytokinin production that is necessary for shoot growth. Summer pruning removes leaves, which affects tree water potential and photosynthesis. Summer pruning has long been regarded as more dwarfing than dormant pruning, but recent research does not support this belief.
72 CONCISE ENCYCLOPEDIA OF TEMPERATE TREE FRUIT Training
Bending a tree's branches from a vertical to a more horizontal position is a method of dwarfing. As a branch is reoriented by bending, terminal extension growth and apical dominance are reduced, and lateral branching is increased. Dwarfing resulting from limb bending is a hormone-controlled mechanism. When branches are bent, tissue is damaged and ethylene is released, which reduces terminal growth and increases lateral budbreak and diameter growth of the bent limb. Bending also affects auxin production and movement in the shoot. Less auxin is available to suppress lateral budbreak, and the auxin concentration is greater on the lower side of the bent limb than the upper side. The response to branch bending is greater in the lower part of a tree than in the upper part of the canopy. Cultivars respond differently to the degree of bending.
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