Influence of Post-Flowering Chemical Thinning on Development and Fruit Quality of 'Fuji Suprema' and 'Maxigala' Apple Trees

Aims: Evaluate possible alterations in the development, anatomy and quality of fruits from 'Maxi Gala' and 'Fuji Suprema' apple plants treated with Metamitrom (MM) and Benzyladenine (BA) alone or in combination, applied at different stages of fruit development in the Midwestern region of the state of Santa Catarina.

Study Design: The experiment was arranged in a randomized block design with five replicates. Place and duration of Study: The experiment was carried out in the municipality of Caçador-SC, Brazil, during the growing season of 2016/2017.

Methodology: Two products, BA (with hormonal action) and MM (photosynthesis inhibitor) were applied individually or in a tank mix in post-flowering periods (in fruits of 5-10 mm and 15-20 mm in equatorial diameter), which were compared with plants with no thinning and manual thinning of both cultivars. Treatments were as follows: Control (no thinning) MM, BA, MM + BA (in fruits of 5-10 mm in diameter); MM, BA, MM + BA, manual thinning (in fruits of 15-20 mm in diameter). The phenological stage of F2 (Full flowering (FF) was observed on September 28, 2016 for both cultivars. Evaluations of the anatomical characteristics of fruits at the time of harvest did not show any alteration in cell size (mean cell area - μm2) and cell density (number of cells per fruit section area); the mean fruit mass was higher in MM 350 mg L-1 (5-10 mm), MM 350 mg L-1 + BA 40 mg L-1 (5-10 mm), and MM 350 mg L-1 (15-20mm) treatments. In the 'Fuji Suprema' cultivar, except for control treatments, MM 350 mg L-1 (5-10mm) and BA 80 mg L-1 (5-10mm), a significant reduction in production was observed (kg plant-1 and fruit-1). While in 'MaxiGala', all the thinning treatments reduced yield per plant. The cultural thinning practice, fruit load management, adapting the number of fruits according to plant size is the most important factor that producers are able to influence. Thinning reduces fruit load in the plant, which allows remaining fruits the possibility of greater growth and size gain. The combination of MM + BA is efficient in the thinning of apple fruits, especially when applied at the beginning of fruit development (5-10 mm in diameter). The application of chemical thinners, such as MM and BA, may influence the early stages of fruit development.