ISHS Acta Horticulturae 653: IX International Symposium on Plant Bioregulators in Fruit Production
THINNING OF 'JONAGOLD' AND 'ELSTAR' APPLES WITH THE COMBINATION OF ETHEPHON AND CPPU |
| Authors: | M. Stopar, P. Zadravec |
| Keywords: | apple thinning, ethephon (2-chloroethyl phosphonic acid), forchlorfenuron (CPPU = N-[2-chloro-4-pyridinyl]-N'-phenylurea) |
| DOI: | 10.17660/ActaHortic.2004.653.12 |
| Abstract:
The combined spraying of ethephon with synthetic cytokinin forchlorfenuron (CPPU) was investigated on seven-year-old ‘Jonagold’ and ‘Elstar’ apple trees / M.9. The application of ethephon a few times after petal fall (PF) at low concentration was aimed to enhance return bloom without affecting fruitlet abscission. The problems of small fruit in high cropping trees should be overcome by spraying of CPPU since its application in general increased fruit size. Successive applications of ethephon at 30 and 50 ppm, alone or in combination with CPPU 5 ppm, were done after PF at weekly intervals. The single application of CPPU at 5 ppm at PF resulted in strong thinning response of ‘Jonagold’ and non significant thinning of ‘Elstar’ apple trees. The yield of fruit from bigger size class was enhanced on both cultivars after CPPU 5 ppm single application. Postbloom ethephon at 200 ppm alone spraying (PF) and/or five weekly applications of ethephon at 30 ppm or 50 ppm (starting at PF) thinned ‘Jonagold’ trees but no significant additional fruit growth was observed. Three weekly applications of ethephon at 30 ppm or 50 ppm (starting at PF) did not affect fruit set or fruit growth of ‘Jonagold’ trees. Moderate thinning of fruitlets was seen on ‘Elstar’ with all ethephon alone treatments (200 ppm, 3x30 ppm, 5x30 ppm, 3x50 ppm, 5x50ppm, weekly intervals starting at PF) but the average fruit weight was not enhanced by treatment. When 50 ppm ethephon was sprayed at five weekly intervals starting at 18 mm fruitlet diameter of ‘Jonagold’ and ‘Elstar’ trees, a weak thinning and no better fruit growth occurred. The combination spraying of ethephon 3x30 ppm + CPPU 5 ppm or ethephon 5x50 ppm + CPPU 2x5 ppm (at weekly intervals starting at PF) resulted in strong thinning response and in enhanced fruit growth for both cultivars. Return bloom was increased significantly and satisfactorily on well thinned ‘Jonagold’ trees, while on ‘Elstar’ no treatment affected better return bloom even in the case of pronounced thinning. | |
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