ABSTRACT
The apple is an important fruit in many cultures; indeed in Australia the phrase of British origin ‘an apple a day keeps the doctor away’ is often stated in reference to the health benefits of eating apples regularly. The cultivated apple probably originated from natives of northern Asia (Siberian, Pyrus prunifolia; Chinese, Pyrus spectabilis; and cherry-crab, Pyrus baccata (Anon. 1898)) and is referred to in historical texts dating back as far as ad 973 (Hogg 1851). Modern large-scale production occurs predominantly in China, Europe, United States, New Zealand and South Africa. Recent research and development has been conducted with the objective to provide the market with consistent quality of consumer-desired fruit, that is, firm (Wills et al. 1980), juicy (Feliciano et al. 2010), highcoloured fruit (Kootstra et al. 1994) with sugar-acid balance typical of the cultivar (Asrey et al. 2008). Recent foci for advancing our understanding of apple tree growth towards the objective of consistently providing the market with consumer-desired fruit include optimizing yield produced per unit orchard area and optimizing quality or ‘marketable yield’. Breeding programmes have released many new cultivars that have improved and/ or distinct characteristics desired by the consumer, in addition to semi-dwarfing and
dwarfing rootstocks. Understanding how rootstocks and scions interact to manifest in various growth attributes of size, architecture and precocity (earliness of flowering and bearing) has been a major focus. Understanding of growth attributes enables managers to design growing systems that allow the tree to fill the allocated canopy space to optimize light capture early in the life of the orchard (and prevent excessive shading after establishment) in order to produce early yields to pay for investments. How tree growth attributes are manipulated through plant management and the use of plant bioregulators (PBRs) to manipulate developmental processes to induce branching and manage vigour is an important aspect for optimizing tree growth. Key manipulations of tree training and pruning to arrive at a desired tree structure that optimizes within canopy light distribution has been an area of significant R&D investment to provide desired fruit quality, particularly size, firmness, colour and sugar-acid levels. Another important area of study has been the manipulation of bud break through either cultural application or application of PBRs to overcome inadequate winter chilling. Finally, in order to inform how best to optimize total light interception and therefore yield, planting systems research that studies interactions of within and between row spacing of a given rootstock/scion combination trained to various tree structure configurations has been investigated.
