Analysis of bud and sylleptic shoot distribution along one-year-old shoots of hazelnut (Corylus avellana)

The comprehension of one-year-old-shoot architecture provides useful information for improving crop management, such as pruning or vegetative/reproductive equilibrium. This work aimed to investigate one-year-old hazelnut shoot structures, in three different treatments: own-rooted plants at two ages (6 or 35 years old) or 6-year-old plants grafted to Corylus colurna seedlings. The experiment was conducted in January 2020 in Deruta, Perugia (Italy). In each treatment, 120 one-year-old shoots of C. avellana ‘Tonda di Giffoni’ were sampled. In each shoot, the position and the number of axillary buds (vegetative (V) or mixed (M)), the presence of blind nodes (B), or male inflorescences (S) were recorded. The frequency of each observation was computed per rank from the base to the tip of the one-year-old shoots. In the 6-year-old plants (either own-rooted or grafted), blind nodes were followed by male inflorescences, mixed buds and then vegetative buds. Grafting seems to change the percentage of mixed and vegetative buds. New shoots borne by the grafted plants seem to be longer than those from own-rooted plants. The length of the shoots is not related to the nut yield in grafted plants while, in own-rooted ones, the longer the shoot the higher the fruit set. Tree aging is not only reflected in shorter shoots. Indeed, 35-year-old own-rooted plants were characterized by the presence of male inflorescences in all the ranks and an average percentage of vegetative buds less than 30%. The different patterns of vegetative and mixed buds, observed along one-year-old shoots, suggest that different strategies for canopy management could be adopted in grafted or own-rooted trees.