Architecture and size relations: an essay on the apple (Malus x domestica, Rosaceae) tree

The influence of tree size independent of age on some architectural features (annual shoot length, lateral branching, flowering) was investigated on 4-yr-old apple (Malus × domestica) trees either own-rooted or grafted on the dwarfing rootstock M.9, giving rise to large and small trees, respectively. Tree size significantly affected the length of the first annual shoot of bottom branches with a lesser effect on the subsequent annual shoots of the same branches and on branches situated higher in the tree canopy. The linear regression parameters, i.e., slopes and intercepts, between annual shoot length and number of growing laterals were affected by the genotype and, depending on genotype, by tree size. Flowering was generally lower, delayed, and more irregular on large trees compared to small trees, with on average similar ranking of genotypes regardless of tree size. This study provides evidence for a specific effect of tree size, as affected by the root system, on architectural development of the apple tree regardless of the genotype. From an architectural viewpoint, the dwarfing mechanism could be interpreted as a faster physiological aging essentially related to the reduction in length of the first annual shoot of bottom branches and the high flowering on this shoot.