Modelling kiwifruit budbreak as a function of temperature and bud interactions

Area of Science:

• Horticultural science
• Plant physiology
• Agricultural modeling

Background:

• Understanding kiwifruit budbreak is crucial for optimizing yield.
• Existing models often use 'chill unit' (CU) approaches.
• Budbreak is influenced by temperature, dormancy-breaking chemicals, and bud interactions.

Purpose of the Study:

• To present and compare two models of budbreak on 'Hayward' kiwifruit canes.
• To evaluate a conventional 'chill unit' (CU) model against an alternative 'loss of potential' (LOP) model.
• To investigate the role of bud-to-bud interactions and environmental factors in budbreak patterns.

Main Methods:

• Developed and compared two budbreak models: CU and LOP.
• The LOP model incorporates bud-to-bud interactions, temperature, and node position.
• Models were calibrated with multi-year regional survey data and tested on independent datasets.

Main Results:

• Both models explained 87% of budbreak variation across sites, years, chemical treatments, and node positions.
• The LOP model describes budbreak patterns along canes, influenced by distal neighbors and temperature.
• Low temperatures (chilling) increase budbreak by reducing suppression, while dormancy-breaking chemicals shorten suppression duration.

Conclusions:

• The LOP model provides a more nuanced understanding of budbreak by considering bud interactions.
• The correlation between chilling and budbreak can be explained by population-level bud interactions.
• These models can inform horticultural practices for improved kiwifruit production.