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ISHS Acta Horticulturae 1221: EUFRIN Thinning Working Group Symposia

The estimation of effectiveness of ATS, metamitron, 
6-BA and ACC in flowers' and fruitlets' thinning of 'Jonagold Red Prince' apple trees

Authors:   I. Szot, T. Lipa, P. Krawiec, A. Basak
Keywords:   climatic conditions, fruit quality, fruit appearance, thinning efficacy, thinners combinations
DOI:   10.17660/ActaHortic.2018.1221.6
Flower or fruitlets thinning is a cultural management practice essential to allow regular yield and high fruit quality. The result of chemical thinning strictly depends upon time of application and type of active substance. One of the formulates that can be used very early in the season for flower thinning is ATS (ammonium thiosulfate). Shortly after, when the diameter of the fruits reaches 6-12 mm, cytokines and metamitron could be used. ACC (1-aminocyclopropane carboxylic acid), a new formulate recently proposed as a thinning agent, can also be used when the fruit diameter reaches up to 20 mm diameter. The aim of this study was to evaluate the effectiveness of some thinning agents for reducing fruit set of ‘Jonagold Red Prince’ apple trees. The following thinning agents, Floredux (ATS), MaxCel (6-BA), Brevis (metamitron) and ACC, were used in various combinations. Floredux + MaxCel/Brevis application caused a strong fruit set reduction of ‘Jonagold Red Prince’ apples and, as a consequence, fruit weight, diameter and length were increased. MaxCel induced the best results similar to that obtained in control with fruits characterized by a better fruit quality. In particular, Maxcell-treated fruits treated reached higher flesh firmness and dry matter values than the.control. All the tested thinners improved fruit commercial distribution reducing the percentage of small fruits (less than 65 mm) and increasing the very large fruits (over 85 mm). The fruit colour of the ‘Jonagold Red Prince’ apple was also improved in particular by ACC application. Every chemical tested increased fruit size and dry matter content as compared to the control.

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