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ISHS Acta Horticulturae 1139: III Balkan Symposium on Fruit Growing

The influence of mechanical thinning on fruit quality and constant bearing of 'Jonagold' apples

Authors:   M. Beber, B. Donik Purgaj, R. Veberič
Keywords:   alternate bearing, Malus domestica, flowering, king flower, flower thinning
DOI:   10.17660/ActaHortic.2016.1139.88
Abstract:
The influence of mechanical thinning with the device “Darwin 200” on the fruit quality and constant bearing of apple cultivar 'Jonagold' was monitored at the Fruit Growing Center Maribor, Slovenia in the years 2013 and 2014. Trees with different flower abundance were selected: in the year 2013 trees from 40 to 140 flower clusters tree-1 and in 2014 trees with 150 to 350 flower clusters tree-1. The “Darwin 200” device was used at constant speed of 6 km h-1 and different axle rotation speed: 200, 240, 270 and 300 rotations min-1 (rpm), respectively. 55 days after full bloom hand thinning was performed. Different quality measurements (size and color classes) as well as the number of flower clusters in the succeeding year confirmed that the combination of the number of flower clusters and the rotation speed were crucial for achieving appropriate fruit quality. Hand thinning had a good effect on fruit quality and constant bearing when the number of flower clusters tree-1 was up to 80. A quality yield and constant bearing was achieved by mechanical thinning and additional hand thinning at the following combinations: 80-120 flower clusters tree-1 thinned with axle speed of 220-240 rpm, at 120-180 flower clusters and 240-270 rpm as well as at 180-250 flower clusters and 270 rpm. At more than 250 flower clusters tree-1 a constant bearing could not be achieved. At axle speed of 300 rpm the trees were damaged and with speeds bellow 200 rpm constant bearing could not be achieved. Based on the results obtained, mechanical thinning with additional hand thinning can be an effective tool for stable bearing of apple trees from year to year.

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