Modelling the architecture of hazelnut (Corylus avellana) Tonda di Giffoni over two successive years

Hazelnut (Corylus avellana) cultivation is increasing worldwide. A 3D model of its structure could improve managerial techniques such as pruning. This study aims to analyse, over two successive years, hazelnut architectural development to implement a functional structural plant model. One hundred and four one-year-old shoots of own-rooted hazelnut trees were selected and analysed in winter 2020 and 2021. Exploratory analyses, generalized linear models and multinomial regression models were used to describe the architectural processes. The existence of sylleptic shoots on hazelnut one-year-old shoots, characterized by the presence of the male inflorescence on apical position, was detected. Along proleptic shoots, the branching pattern was described by (i) blind nodes located in the proximal part (ii) sylleptic shoots and mixed buds in the median part (iii) vegetative buds in the distal part. Apical bud died during the growing season, suggesting that Tonda di Giffoni has a sympodial branching. The models revealed dependencies among buds located at the same node, in the case of proleptic shoots. Especially, the probability of a bud bursting depended on both its type (i.e. mixed or vegetative) and the presence of other buds, either mixed or vegetative. Based on these local models and on a flow diagram, which defines the steps that led to the construction of hazelnut tree architecture, the first functional-structural plant model of hazelnut tree architecture was built. Further experiments will be needed and should be repeated over the following years to extend this study towards the juvenile phase and tree architecture over time.