S16 - Session O2 - Studying spatial variability of fruit size within the tree canopy with a functional-structural plant model

Authors: Inigo Auzmendi *, Jim Hanan

For most fruits, size at harvest is considered an important quality parameter. Within a tree canopy, fruits of different sizes are usually found. Carbohydrate availability during the growth period is one of the factors that affect fruit size. In turn, this carbohydrate availability depends on carbon assimilation through photosynthesis, as well as carbohydrate distribution between competing individual organs, e.g. leaves, stems and fruits. We previously designed and implemented a functional-structural plant model that simulates daily growth of individual organs during one growing season. This model assumes branch autonomy and competition for carbohydrates within individual branches, using as input the architecture of a tree measured in the field. One of the simulation outputs is the size and spatial coordinates of each fruit within the tree canopy. Our aim is to analyze the fruit size variability within the tree to determine spatial patterns in the canopy that are emergent properties of the model. This would help us to test if the model could reproduce realistic spatial patterns of fruit variability considering only carbohydrate balance at individual organ level. We performed virtual experiments and simulated individual fruit size at harvest after one growing season. Fruit size distribution was analyzed in different quadrants of the plant according to height and aspect: north, east, south and west. Fruit size distribution was significantly different in some quadrants, and this pattern matched observations in field experiments. The model helps us to understand better some factors that affect fruit size, in this case carbohydrate availability, and realistically simulated the spatial differences in fruit size within tree canopies.