Apple Tree Physiology – Implications for Orchard and Tree Management

INTERNATIONAL DWARF FRUIT TREE ASSOCIATION Apple yield and fruit quality are the end result of myriad cultural practices (e.g., pruning, thinning, spraying), environmental inputs (e.g., light, carbon dioxide, water, nutrient supply) and physiological processes (e.g., leaf area development, light interception, photosynthesis, respiration). All of them are truly essential contributors to fruit production. That does not mean, however, that any one resource or process is necessarily controlling the variation in yield and fruit quality of apple orchards. There are only two possible means to improve crop performance: 1) increase total dry matter yield and/or 2) increase the magnitude of partitioning of dry matter toward the fruits. This review will emphasize the key processes of tree canopy light interception/distribution and carbon partitioning in limiting apple yields and discuss the implications of these processes for grower practices of orchard/tree design and canopy management. Although factors such as frost, drought, nutrient deficiencies and incidence of diseases can limit fruit yields, in a healthy, well-maintained and supplied orchard system these factors are less critical in determining overall yield and fruit quality.