Effect of bending on the dynamic changes of endogenous hormones in shoot terminals of ‘Fuji’ and ‘Gala’ apple trees

Abstract

Branch bending has been practiced for decades as an effective means of inducing floral buds in ‘Fuji’ apple in China. Endogenous hormones play an important role in apple flowering. The main purpose of this study is to investigate the hormone concentrations (ABA, ZR, IAA and GA) in spurs, medium and long shoot terminals of ‘Fuji’ and ‘Gala’ apple trees subjected to bending of different angles (70°, 90° or 110°). In both cultivars, the proportion of floral buds and spurs increased, but that of medium and long shoots decreased with increasing bending angles. The ABA and ZR concentrations in shoot terminals increased, but the IAA and GA concentrations decreased as the bending angles increased from 70° to 110°. The ZR concentration increased monotonically in spurs apexes, but in medium and long shoot terminals it increased from a minimum on May 10 to a maximum on June 20 for ‘Fuji’ apple trees or on July 20 for ‘Gala’ apple trees, and then decreased thereafter. It was also observed that the ‘Gala’ apple trees had a higher ABA concentration but a lower IAA concentration in shoot terminals than the ‘Fuji’ apple trees. The ZR concentration in spurs apexes of ‘Gala’ apple trees was higher before July 1, and the GA concentration was higher before June 20, but lower after July 20 than the ‘Fuji’. The (IAA + GA + ZR)/ABA ratio of spurs apexes in ‘Fuji’ apple trees decreased with increasing bending angles during the whole growth season, with a significant difference between those bent at 110° and those bent at 70°. There was no significant difference for the ‘Gala’ apple trees. The (IAA + GA + ZR)/ABA ratio peaked on June 20, and it was higher in ‘Fuji’ than in ‘Gala’ apple trees throughout the study period.