Competition-based Model of Pruning: Applications to Apple Trees

Pruning is widely used in horticulture to control tree shape and balance between vegetative and reproductive growth. Several pruning models have been developed. They are based upon competition mechanisms and transport network to distribute resources to different sinks using either a source-sink allocation function (Borchert and Honda, 1984; de Reffye et al., 1999; Balandier et al., 2000) or an electrical analogy (Lopez et al., 2008). In pruning models, reaction to pruning originates from competition between organs (de Reffye et al., 1999), or reassignment of bud fates depending on apical dominance (Borchert and Honda, 1984; Lopez et al., 2008), or from new bud-break occurrences (Balandier et al., 2000). The output of these models were compared in a qualitative way to small samples of real observations. In this paper, we present a new model based upon resource partitioning between competing sites (with no explicit transport) and growing processes so as to study and simulate the development and pruning reactions of fruit trees. It is supported by recent studies carried out on a large data set from two apple cultivars (880 trees) that show both local and distant reactions to pruning (Fumey et al., submitted). Although apple tree model like MappleT (Costes et al., 2008) that combines stochastic (branching pattern) and mechanistic (bending) modules already exists, it does not include resource allocation mechanism nor pruning reactions. The present model uses an abstract resource allocation with a notion of context for each meristem, which is used in a botanical sense, taking into account the meristem position in the plant architecture as well as its environment. First results show that realistic pruning reactions can be obtained as an emerging property of the model.