Zonal Chemical Signal Pathways Mediating Floral Induction in Apple

Area of Science:

• Plant Physiology
• Horticultural Science
• Metabolomics

Background:

• Apple trees exhibit biennial bearing, alternating heavy and light crop loads, due to fruitlets inhibiting adjacent bud flowering.
• This cycle is influenced by phytohormones locally emitted from leaves and fruitlets, impacting floral induction (FI).

Purpose of the Study:

• To investigate the metabolic pathways and signaling molecules activated during floral induction (FI) in apple buds.
• To understand the biochemical basis of biennial bearing and identify potential targets for crop load management.

Main Methods:

• Young 'Ruby Matilda' apple trees were subjected to zonal crop load treatments.
• Buds were collected during the floral induction phase (within 60 days after fruitlet set).
• Metabolomics profiling was performed to analyze differential metabolic pathways and key signaling molecules.

Main Results:

• Significant metabolic differences were observed in trees and leaders exhibiting high return bloom.
• Elevated levels of compounds in the cytokinin, abscisic acid (ABA), phenylpropanoid, and flavanol chemical classes were detected.
• Specific cytokinins (adenosine, inosine) and ABA phytohormones were identified as key players.

Conclusions:

• Floral induction in apple buds is associated with distinct metabolic shifts, including increases in cytokinins and ABA.
• These findings provide insights into the hormonal regulation of flowering and biennial bearing.
• Identified phytohormones offer potential targets for developing plant growth regulators to manage apple crop loads.