TITLE:
Gibberellic Acid4+7 and Benzyladenine, Cambium Disconnection, Nitrogen, and Tip Removal Influence on Branch Induction in Newly Planted Poorly Feathered “Fuji” Apple Trees
AUTHORS:
Shahla Mahdavi, Esmaeil Fallahi, Gregory A. Lang, Bahar Fallahi
KEYWORDS:
Bark Girdling, High Density Orchard, Malus domestica
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.11 No.3,
March
27,
2020
ABSTRACT: The use of well-feathered nursery trees on dwarfing
rootstocks is crucial for establishing high-density apple orchards to ensure
early production. Training trees to develop a tall spindle canopy architecture
has gained popularity in high-density orchards during the past decade. However,
commercially produced nursery trees often lack feathers or are unevenly
branched, making initial training decisions difficult and delaying precocious
fruiting. In this project, we studied the vegetative meristem activation
response to partial scoring or partial girdling of the bark cambium above the
bud, with and without application of 500 ppm Promalin (gibberellin4+7 + benzyladenine), tip removal of the tree leader at the silver tip
stage on April 23, 2019, Promalin spray at 500 ppm at post-bloom
stage on May 7, 2019, and nitrogen (N) as UAN-32 (32% N) application at
five levels (60, 80, 100, 120, or 140 g actual N/tree) on June 20, 2019, in
newly planted un-feathered or unevenly branched “Aztec Fuji” trees on Budagovsky 9 (Bud 9) in southwest Idaho, USA. Grower’s Short
Cut trees received a heading cut to the leader at 60 cm above the ground and
resulted in the emergence of 5 - 6 strong branches near the
heading cut. These trees had larger trunk cross-sectional areas than scored or
girdled trees. Scoring or girdling, with or without Promalin, significantly
improved branching by increasing the number of branches and bourse shoots. In
many cases, the effects of partial scoring, with or without Promalin, were
similar to those of bark girdling which is a more risky and time-consuming
process. Branches induced by scoring and girdling had sharper crotch angles
relative to the vertical leader. Spraying Promalin during the post-bloom stage
at 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 impact
branch induction.