Effects of heading-back pruning on shoot growth and IAA and cytokinin concentrations at bud burst of columnar-type apple trees

Abstract

To elucidate the possible relationship between growth characteristics and apical dominance of columnar-type apple trees, the growth response to heading-back pruning and the concentration of indoleacetic acid (IAA) and cytokinins in apical and lateral buds on one-year-old shoots after sprouting were investigated. Terminal shoot growth in columnar-type 'Trajan' was not inhibited, whereas distal lateral shoots displayed significant length growth by heading-back pruning. The IAA concentration of columnar types was higher in apical shoots than in lateral shoots. The cytokinin concentration of both apical and lateral shoots was higher in columnar type than in the normal one. The kind of cytokinins that directly influences the growth regulation of columnar types was not determined. The ratio of total cytokinins to IAA concentration for cultivars and nodal positions was not significantly different suggesting that apical dominance is more involved in growth characteristics of columnar type than it is in normal apple trees.