|Authors: ||J. Racsko, D.D. Miller|
|Keywords: ||Malus × domestica, return bloom, fruit set, gibberellic acid, GA1, GA3, GA4, GA7, fruit quality, alternate bearing index|
A field trial was carried out in an experimental apple orchard with the regular-cropping ‘Royal Gala’ and the alternate-bearing ‘Vista Bella’ over five consecutive years.
Both were grafted onto M.9, MM.106, and seedling rootstocks representing dwarf, semi-vigorous and vigorous growth habit, respectively.
Flowering time of both cultivars was not influenced by alternate bearing and rootstocks.
The rate of fruit set was significantly higher for off-year trees on all three stocks.
The amount of flower-inhibiting gibberellins (GA3 and GA7) in the seeds was significantly higher and the flower promoting GA4 was lower for on-year trees, especially on seedling rootstock.
No significant differences, however, were observed in GA1 content among rootstocks.
Better fruit quality parameters were usually measured for fruit from off-year trees on M.9 and MM.106 rootstocks.
There was no significant differences in quality between on-year and off-year on seedling.
For describing the alternate bearing habit more accurate, a modified alternate bearing index (AIm) was developed based on the flower production of the cultivars.
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