Effects of Pruning on the Apple Tree: from Tree Architecture to Modeling

Arboricultural practices such as pruning, artificial bending or fruit thinning are crucial interventions in orchard management and are used for controlling tree size, penetration of light into the canopy and the equilibrium between vegetative and reproductive growth. The aim of this project is to explore the possibility of integrating such practices in a model of apple tree development. To this end we designed field experiments to study the effects of pruning (thinning or heading cuts) on two apple cultivars with contrasted architecture, ‘Fuji’ and ‘Braeburn’. The results of these first experiments showed that the studied cultivars had significantly different reactions to pruning: ‘Braeburn’ trees were penalized more than ‘Fuji’ trees in terms of the total number of internodes despite the fact that a greater number of internodes had developed. Thinning cuts of laterals tended to be compensated by an increase in lateral branching. Results also indicated that trees which had been pruned tended to develop trunks with similar number of internodes than control trees (which were not pruned). These experiments constitute a first step for assessing the rules underlying tree responses to pruning, which will be further integrated in a model of growth. Introduction L-systems are being increasingly used to model the development of plants in agronomical applications (e.g. ADEL-maize, Fournier et al., 1999; L-Peach, Allen et al., 2005, Lopez et al., in press). Following this trend, we devised an L-system-based simulation project of the development of apple tree architecture. This approach features a new combination of stochastic and mechanistic models describing branching patterns and branch bending due to gravity (Smith et al., 2007, Costes et al., in press). The model, called MappleT, does not take into account arboricultural practices such as pruning, artificial bending or fruit thinning. Nevertheless, these methods of pruning are crucial interventions in the management of orchards and are used for controlling tree size, light penetration within the canopy and the equilibrium between vegetative and reproductive growth. Previous studies have analyzed tree responses to pruning and impacts on fruiting (Saure, 1987; Marini, 1987; Li et al., 2003) but few have dealt with tree responses in terms of architectural development. The aim of this project is to integrate pruning techniques into a reactive model of tree growth. This paper describes the field experiments that were designed to study pruning effects on two apple cultivars with contrasted architecture, ‘Fuji’ and ‘Braeburn’. ha l-0 08 38 83 3, v er si on 1 26 J un 2 01 3 Author manuscript, published in "9th International Symposium on Integrating Canopy, Rootstock and Environmental Physiology in Orchard Systems (2008)"