Thinning of ‘Eva’ Apple with Plant Growth Regulators

Aims: The aim of this research was to evaluate the effects that cause the plant growth regulators, namely naphthalene acetic acid (NAA), 6-Benzyladenine (BA) and Promalin® (6- benzyladenine (BA) with the gibberellic acid GA 4+7), on thinning efficacy and return bloom of ‘Eva’ apple trees.

Study Design: The experimental design used was a randomized complete block design, with four replications, with two plants per treatment in each block, following a one-step scheme with 13 treatments for the thinning factor. Obtained results were submitted to analysis of variance, and means were compared by Tukey test with a 5% probability of error.

Place and Duration of Study: The experiment was carried out during the agricultural cicles 2012/2013 and 2013/2014 in a commercial orchard located in the municipality of Morro Redondo, RS, Brazil.

Methodology: Plant growth regulators were applied in both cicles as follows: Promalin® was sprayed at the full bloom (80%) period at doses of 0.5, 1.0, 1.5 and 2.0 mL L-1; NAA and BA were sprayed in fruits with 5-7 mm diameter, at doses of 5, 10 and 15 mg L-1 and 50, 75, 100 and 125 mg L-1, respectively, and hand fruit thinning was performed after full bloom.

Results: Number of fruit per plant, the density of fruits by the trunk cross-sectional, yield per plant and the return of bloom in the second cycle were evaluated in the field. Fruit flesh firmness, total soluble solids, fruit diameter, fruit length and mean fruit mass were evaluated at Laboratório de Agronomia (LabAgro), Universidade Federal de Pelotas. With Promalin® at different concentrations, the results were statistically similar to the hand fruit thinning, so this procedure can be another alternative for thinning.

Conclusion: The plant growth regulator NAA reduced the harvesting load but caused a negative response and the plants formated of fruits small. The BA-based treatments were more efficacy for reducing fruits load, increased fruit size and accelerated the flowering return.