Trunk Constriction Effects on Vegetative Vigour and Yield Efficiency in Olive Tree (Olea europaea L.)

Tree vigour is one of the most important issues in super-high density olive orchards (~1,600 tree ha^-1). Tree vigour could be limited by horticultural practices such as pruning and fertilization but such practices have a limited effect and increase growing costs. The aim of this work was to test a new technique based on the application of a constriction to the trunk in order to obstruct the flow of sap in xylem and phloem. To this end, on 5 cultivars trained in a super-high density olive orchard in Central Italy, constrictions were applied by a plastic strap in 2009 and 2010, and were removed at the end of the following year. At the end of the experiment, constricted trees had smaller vegetative growth than the control trees. During the first experiment (2009), in the constriction year, yield efficiency was higher in constricted trees. In the second year, low vigour cultivars (‘Arbequina’, ‘Maurino’ and ‘Moraiolo’) had a consistent reduction of yield, while vigorous cultivars (‘Leccino’ and ‘Frantoio’) had similar yield but a slightly increased yield efficiency. No effect was detected in fruit characteristics, but the oil phenol content was higher in the constricted trees. In the second year experiment (2010), similar results were obtained, but yield efficiency increase and vegetative growth reduction were lighter because the trees were one year older than those of 2009 experiment. Trunk constriction was a successful technique for reducing tree vigour and enhancing tree yield efficiency, especially in vigorous cultivars.