Abstract:

The development of effective flowering regulation techniques is of great significance for improving blueberry yield. This study investigated the regulatory effects of mild apical dominance suppression on reproductive growth in blueberries, aiming to provide a theoretical basis for optimizing flowering and fruiting management practices. Two consecutive trials were conducted using ‘Premier’ blueberry as plant material, with apical bud removal (topping) and non-removal (non-topping, the control) treatments. Morphological observation, statistical analysis, and quantitative PCR were employed to systematically compare flowering and fruiting performance in lower shoot nodes and to analyze the expression dynamics of key flowering-related genes VcFT and VcFT-like in corresponding leaves. The results showed that flower number, flowering rate, fruit setting number, and fruit setting rate all decreased progressively with lower node positions. Among these, flower number and flowering rate were consistent across both trials, and the flowering rate of topping group was consistently higher than that of the control. However, the number of flowering nodes, fruit setting number, and fruit setting rate showed annual variation: topping significantly increased the number of flowering nodes in the first trial but led to poorer fruit setting, whereas the second trial showed significantly improved fruit setting rate and fruit setting number in the topping group. Gene expression analysis indicated that VcFT expression increased progressively during floral induction, with a more pronounced increase under topping treatment and a delayed expression peak in lower nodes. In contrast, the expression of VcFT-like was high only at the initial stage of induction, then declined continuously and was nearly undetectable at mid-to-late phases, with no significant differences between the two treatments. In conclusion, topping treatment effectively promotes flower bud formation and increases flower number in lower nodes of blueberry branches. However, its effect on fruit setting may be constrained by environmental conditions and management practices, leading to inconsistent results between years. VcFT plays a positive regulatory role in floral induction, influenced by topping treatment and node position, while VcFT-like may be involved mainly in the early stage of floral induction. These findings reveal that mild apical bud removal promotes flower bud formation at lower nodes on blueberry branches, providing a theoretical reference for flowering and fruit setting regulation in blueberry.

Key words: blueberry, topping, flowering, fruit setting, node, gene expression