Abstract
Yield reduction over the years is a phenomenon that affects many fruit tree species, including hazel (Corylus avellana). Studying plant architecture could provide useful information for improving crop management, such as pruning, to reduce the impact of yield reductions. This study aimed to compare the relationship between bud composition and shoot length in hazel shoots. The experiment was carried out in January 2020 and 2021 in Deruta, Perugia (Italy). In 2020, 120 1-year-old shoots of C. avellana 'Tonda di Giffoni' were sampled. In 2021, the same observations were performed on lateral and apical 1-year-old shoots that had burst from parental buds in spring 2020. Depending on its length, each shoot was sorted into four categories: short (Sh) when shorter than 5 cm, medium (Me) when between 5 and 20 cm, long (Lo) when between 20 and 40 cm, and very long (VLo) when longer than 40 cm. For each shoot, shoot length, axillary and apical bud fate was recorded at each node: vegetative bud, latent bud, catkin, and mixed bud (V, B, C, and M, respectively). Percentage of lateral mixed buds was higher in longer shoots than in shorter ones while that of vegetative buds remained constant whatever the length. Fruit set, computed as the ratio between the number of nuts and the number of mixed buds, was significantly higher in Lo and VLo shoots. It was observed that the length of lateral proleptic shoots, developed in 2021, was related to the length of the bearer shoot from which it was developed. Proleptic lateral Sh shoots were the most frequent among all length categories while longer proleptic shoots (Lo and VLo) were originated only from Lo and VLo shoots. Managing tree architecture, considering a good balance between long and short shoots, and mixed and vegetative buds, could help control and prevent yield decrease in hazelnut trees.