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

For most fruits, size at harvest is an important quality parameter. However, spatial variation of carbohydrate assimilation and distribution between competing organs during the growth period results in varied fruit sizes. We use a functional-structural plant model that simulates daily growth of individual organs during one growing season, assuming branch autonomy and competition for carbohydrates within individual branches, starting with the architecture of a tree measured in the field. To test if the model can 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 spatial variability was analyzed in different quadrants of the plant according to height and exposure: north, east, south and west and was found to be significantly different in some quadrants. The model realistically simulated the spatial differences in fruit size within the tree canopy, leading to better understanding of how carbohydrate availability affects fruit size.