Investigating the seasonal progression of bud dormancy as a function of temperature

Previous trials determined bud dormancy progression as a function of time, i.e. depth of dormancy was plotted over calendar days. However, these dormancy progression curves (DPC) could not be explained in terms of the Utah Model. Shoots entered dormancy long before any Chill Units (CU) accumulated. In fact, in very warm areas, deepest dormancy was attained before any significant CU had been acquired.

The intended objective of this project was to be twofold: Firstly, the existing dormancy curves would have been studied in conjunction with other chill accumulation models that are better suited to warm growing conditions prevalent in the apple growing regions of South Africa, e.g. The Dynamic Model. Secondly, this project proposed reworking the depth of dormancy data collected from 2005-2009 as a function of chill accumulation (temperature) rather than calendar days (time) in order to better understand the seasonal progression of bud dormancy.

By approaching the progression of dormancy from a different perspective, it is possible that a better understanding of dormancy and in particular entrance into dormancy would have been achieved. An understanding of how and why dormancy progresses during a season would ultimately benefit future dormancy research.

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Due to time constraints arising from the lack of post graduate research students for other dormancy projects, this project was not executed during the 2014-2015 financial year. Consequently the allotted finance for the project was never allocated to the project and remained in the HORTGRO account.  Although this project was never undertaken, it does not detract from the fact that it is a viable and important research topic which should be attempted in the future if capacity within the dormancy group is available. A new project application would then be submitted.