Abstract
Abstract: The objective of this work was to evaluate the feasibility of using ammonium thiosulfate as a chemical blossom thinner in 'Maxi Gala' apple (Malus domestica) trees and its effects on fruit quality. The experiment was carried out in an experimental orchard in the Southern Brazil, in a randomized complete block design, with five replicates. Ammonium thiosulfate was sprayed on the apple trees at the full bloom stage, at 0, 1.5, 2.5, and 3.5%. Evaluations were performed for the effects on crop load, fruit set, yield efficiency, and fruit quality parameters such as weight, shape, total soluble solids, seed number, flesh firmness, color, and russeting occurrence. Ammonium thiosulfate at 2.5% is effective to reduce crop load and to improve fruit quality. The thinning effect of ammonium thiosulfate is not dependent on the weather conditions during the crop season. The rate of 3.5% of ammonium thiosulfate causes overthinning and does not result in the improvement of fruit quality.
Highlights
In 2015, Southern Brazil produced 1,163,744 tons of apples on 36,089 hectares (Anuário..., 2016)
When thinning was done at blossom stage, there was a significant increase of 30 g in fruit weight, in comparison to thinning done at four weeks after full bloom
After ammonium thiosulfate (ATS) spraying, fruit set decreased inversely proportional to the rate of blossom thinner application (Table 1)
Summary
In 2015, Southern Brazil produced 1,163,744 tons of apples on 36,089 hectares (Anuário..., 2016). Blossom thinning has the greatest potential to increase fruit quality at harvest, as fruit size (weight) is highly correlated with cell numbers (Link, 2000; Lakso & Goffinet, 2013; Jakopic et al, 2015). When thinning was done at blossom stage, there was a significant increase of 30 g in fruit weight, in comparison to thinning done at four weeks after full bloom. Flower thinning increases fruit size by 30% when it is done at flowering, in comparison to when thinning is performed after the “June drop” (Link, 2000), and improves bloom return for the following year and increases fruit total soluble solids (Meland, 2009)
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