Different Sources and Concentrations of 6-BA in Chemical Thinning of Post-flowering in Apple Trees

Aims: Evaluate the efficiency of sources and dosages of 6-benzyladenine in the chemical thinning of the apple tree ‘Fuji Suprema’, as well as possible histological changes in the fruits produced, in the Midwestern region of the state of Santa Catarina.

Study Design: The experiment was arranged in a randomized block design and replicated six replications.

Place and Duration of Study: The experiment was carried out in the municipality of Caçador, Brazil (latitude 26º46 'S, longitude 51º W, altitude 960 meters), during the growing season of 2016/2017.

Methodology: Two commercial products based on 6-BA (Benzyladenine), Exilis® and Maxcel®, both with 2% BA in their composition, were tested and applied individually in post-flowering period (in fruits of 5-10 mm), which were compared with plants with no thinning and manual thinning. Treatments were as follows: Control (no thinning); manual thinning; Exilis® (1.5, 3.0, 4.5 and 6.0 L ha-1) and Maxcel® 4.5 L ha-1), using a spray volume equivalent to 1000 L ha-1. The fruit set and the number of fruit per cm2 branch, was reduced in treated plants, regardless of the concentration of BA or formulation used. The productivity ranged from 38 to 56.5 t ha-1 in the treatments of Exilis®, 60.5 t ha-1 in manual scaling and 24.5 t ha-1 in the Maxcel® 4.5 L ha-1, characterizing excessive thinning. BA is efficient in fruit thinning in 'Fuji Suprema' apple trees, being the reduction of fruiting, and increase of fruit size, proportional to the applied concentration. There may be differentiated efficiency of the product by its formulation, even though they have concentrations of active ingredient equivalent. Exilis® was efficient in thinning of apple "Fuji Supreme", when applied to fruit 5 to 10 mm in diameter reduced the need for manual thinning, without causing toxicity. BA can promote the increase in the cell density of fruits produced in proportion to the applied concentration.