Effect of growth regulators on the sap flow in the apple tree

This research paper presents the results of a field trial performed in a young orchard with apple cultivar 'Gala Galaxy', on the rootstock 'M9'. In November 2012, nursery “knip” trees were planted at the distance 3×1 m. In the first growing season (2013) the experimental plot was separated in a randomized block system of four treatments. Eight apple trees (2 for each variant), in the stage of nursery trees production were treated with growth regulators GerBA 2.5% (benzyl adenine), and Progebalin 2.5% (gibberellins A₄₊₇ + benzyl adenine). Besides, two other treatments were included: pinching (i.e., removal of terminal leaves) and control (untreated). The sap flow measurement was examined through sap flow sensors based on stem heat balance method. The measuring interval was every minute with 1 s warm-up and storing interval every 15 minutes during period July-September 2013. Also, at the same time vapor pressure deficit (VPD), potential evapotranspiration (PET), soil moisture, soil and leaf temperature were measured. By the results obtained, the treatments with GerBA 2.5%, and Progerbalin 2.5% gave higher values of sap flow (79.9 and 78.09 g h^-1) in relation to other treatments, pinching and control, respectively; (71.04 and 70.09 g h^-1). It is also noticed that strong correlations between sap flow, VPD, PET, soil moisture, soil and leaves temperature exist.