Gibberellic Acid4+7 and Benzyladenine, Cambium Disconnection, Nitrogen, and Tip Removal Influence on Branch Induction in Newly Planted Poorly Feathered “Fuji” Apple Trees

摘要

The use of well-feathered nursery trees on dwarfingrootstocks is crucial for establishing high-density apple orchards to ensureearly production. Training trees to develop a tall spindle canopy architecturehas gained popularity in high-density orchards during the past decade. However,commercially produced nursery trees often lack feathers or are unevenlybranched, making initial training decisions difficult and delaying precociousfruiting. In this project, we studied the vegetative meristem activationresponse to partial scoring or partial girdling of the bark cambium above thebud, with and without application of 500 ppm Promalin (gibberellin4+7 + benzyladenine), tip removal of the tree leader at the silver tipstage on April 23, 2019, Promalin spray at 500 ppm at post-bloomstage on May 7, 2019, and nitrogen (N) as UAN-32 (32% N) application atfive levels (60, 80, 100, 120, or 140 g actual N/tree) on June 20, 2019, innewly planted un-feathered or unevenly branched “Aztec Fuji” trees on Budagovsky 9 (Bud 9) in southwest Idaho, USA. Grower’s ShortCut trees received a heading cut to the leader at 60 cm above the ground andresulted in the emergence of 5 - 6 strong branches near theheading cut. These trees had larger trunk cross-sectional areas than scored orgirdled trees. Scoring or girdling, with or without Promalin, significantlyimproved branching by increasing the number of branches and bourse shoots. Inmany cases, the effects of partial scoring, with or without Promalin, weresimilar to those of bark girdling which is a more risky and time-consumingprocess. Branches induced by scoring and girdling had sharper crotch anglesrelative to the vertical leader. Spraying Promalin during the post-bloom stageat 500 ppm was not as effective as scoring or girdling to initiate branches.Additional N rates or removal of the leader tip did not significantly impactbranch induction.