Modeling the development of transport structures in apple (Malus × domestica Borkh.) fruit using X-ray micro-computed tomography (µCT)

The void network and vascular system plays an important role in the transport of gases, water and solutes. How these structures develop during fruit growth will affect the central metabolism of the fruit and the overall quality when the fruit is harvested. X-ray micro-Computed Tomography (µCT) provided a unique insight into the void network and vascular system in a developing apple (Malus × domestica Borkh) fruit. Microstructural analysis revealed a highly branched void network and vascular system across the whole fruit which was observed all throughout the development stage. Air voids and cells increased in size in both core and cortex of apples with voids in the core smaller than that of the cortex. Porosity and connectivity of void space network increased. Vascular bundles grew in total length from 2.81 (±0.95) m at 9 weeks after full bloom to 17.42 (±3.96) m at 22 weeks. When this was expressed on a fruit volume basis, the young developing apple was found to have a more extensive vascular network compared to mature fruit with values of 11.42 (±1.67) cm cm^-3 at 9 weeks after full bloom to 4.97 (±1.49) cm cm^-3 at 22 weeks. The branching points of the cortical vascular network towards the skin were found to increase fourfold from 9 weeks after full bloom until the end of the growth season (week 22). The void network presented can be used to model respiratory activity and help explain hypoxic condition leading to physiological disorders. The vasculature model, on the other hand, can be used to model water and nutrient flow in the fruit. By connecting previous vasculature models for wood, root and leaf, a virtual tree could be generated.