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ISHS Acta Horticulturae 732: VIII International Symposium on Canopy, Rootstocks and Environmental Physiology in Orchard Systems


Author:   T.L. Robinson
Keywords:   planting system, tree density, tree shape, rootstock, light interception, light distribution, feathered trees, training, limb angle, pruning, profitability, genome mapping
DOI:   10.17660/ActaHortic.2007.732.57
Over the last 60 years, planting densities for apple, pear, peach, cherry, apricot and plum have all increased as improved management systems have been developed and the need for earlier production has become critical. For apple and pear, dwarfing rootstocks have been the key to the dramatic changes in tree size, spacing and early production. However, other improvements such as the development of feathered trees, development of minimal pruning strategies and physiological studies of limb angle have also contributed to the dramatic changes in tree density. Other studies on light interception and distribution have led to practical pruning strategies and improved tree forms. Advances in other fruit crops have generally followed advances in apples but since they have not had the benefit of fully dwarfing rootstocks, their planting densities have not increased as high as apple and pear. With cherry, semi-dwarfing precocious rootstocks have induced over-cropping which has required new pruning and cropload management strategies to obtain large fruit size. For cherry, peach, and plum, future increases in tree density depend on the development of improved dwarfing rootstocks. With apple and pear, the relentless march toward higher and higher tree densities over the last 50 years has recently been limited by economic factors, especially the price of trees. Economic studies have shown that the optimum tree density for apple is less than the maximum density that can be successfully managed. These studies have shown that the price of trees becomes very critical as tree density increases. Further increases in tree density will depend on reducing tree costs. As we look to the future, there are two possible scenarios. 1) The continued incremental improvement in our understanding of plant physiology that will lead to continued incremental improvements in orchard management or 2) Dramatic changes in orchard production system through genetic engineering. The first scenario will see continued understanding of the mechanisms of dwarfing, precocity and rooting which will lead to new rootstocks and better management of rootstocks for optimum performance. The second scenario could lead to identifying genes that control dwarfing, precocity and rooting and incorporating those characteristics into new varieties thus eliminating the need for the rootstock. Similarly, if the heterozygosity of Malus and Prunus species could be overcome, a seed based system of plant propagation could be envisioned which would dramatically change orchard planting densities and management. With either scenario, there is a need to improve our understanding of the genetic control of vegetative growth, flowering and fruit growth as well as improve our understanding of the physiology of pruning and thinning.

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