Increasing on Fruit Set and Yield of ‘Monalisa’ and ‘Maxi Gala’ Apple Trees Using Plant Growth Regulators

Abstract

Aims: To evaluate the effect of different plant growth regulators on fruit set and yield of apple trees in mild winter conditions. Study Design:  The experiment was arranged in a randomized block design. Place and Duration of Study: The experiments were carried out in southern Brazil, municipality of Caçador/SC, during the cycle 2016/2017 to 2019/2020 in the 'Monalisa'/M9 and another experiment with cultivars Maxi Gala/M9 and Monalisa/M9, in 2018/2019 and 2019/2020. Methodology: The following products were tested: TDZ (Thidiazuron) Naphthalene acetic acid (NAA), Maxcel®, Ethrel®, Promalin®, Ammonium thiosulfate, and the combination TDZ + Viviful® + Retain®. The following evaluations were carried out: fruit set, fruit yield per plant and per hectare; number of fruits per plant, average fruit mass, the red skin color of fruits, degree of russeting and classification of fruits by size. Results: In 'Monalisa' apple trees, TDZ alone and combined with PCa + AVG increases the fruit set, when applied in full bloom, while TDZ alone and NAA applied in full bloom increases the productivity. TDZ alone reduces return bloom and induces greater alternate bearing while, combined with PCa + AVG does not cause bearing alternation; however, it reduces the average fruit mass. BA + GA reduces the productivity of 'Monalisa' apple trees. The fruit set increased significantly with AVG treatments 52 ppm, 104 ppm, and 156 ppm, while the yield per plant, number of fruits per plant and estimated productivity, all treatments were significantly superior to the control treatment with the exception of AVG 52 ppm, on the Cv. Monalisa. The control treatment and AVG, 104 ppm and 156 ppm presented fruits with larger caliber and only AVG 26 ppm showed a lower percentage of fruits in the class of higher coloration, in comparison to the other treatments. The russeting incidence did not present significant differences in the cultivar Monalisa and Maxi Gala. None of the variables were significantly altered by the application of Retain® in the Cv. Maxi Gala.