Abstract/Summary

The increase in temperature as a consequence of climate change is predicted to impact adversely on UK apple production by affecting the dormancy cycle. Warmer winters, and an increased risk of frost damage due to earlier bud break, are of major concern to UK growers. Although chilling and heat accumulation models are often used to predict time of bud break and anticipate cultivar suitability to new climes, existing models do not consider different cultivar responses or climate change scenarios and so are of limited use. The aim of this PhD research programme was to improve our understanding of the temperature effect on the dormancy cycle in a range of apple cultivars, and to develop cultivar-specific models to predict cultivar suitability in a climate change context. All experimental work was carried out in the UK between 2017 and 2021, using a combination of methodologies and plant materials including excised shoots, potted trees, floral buds, and xylem sap from orchard trees. Data were collected through experiments in controlled environment conditions, from UK apple orchards, and from analytical work in the laboratory. The depth of dormancy was highly variable between cultivars, as evidenced by the finding of different sensitivities to warm temperatures during ecodormancy. A lower optimum temperature for chilling accumulation was observed compared to previous models, indicating that future reductions in winter chill accumulation could be more severe than predicted. A new chilling model was created, the Malus model, which represents a better approximation of temperature contributions towards chilling accumulation. Results also indicated a partial overlap between chilling and heat accumulation, and a new modelling approach was developed that accounted for the correlation between both temperature-driven processes. Changes in carbohydrate concentrations in apple buds and xylem sap during winter occurred in parallel to chilling and heat accumulation, indicating a link between carbohydrate dynamics and the progression of dormancy. The outputs from this PhD research programme corroborate the industry’s concern that warmer winters will pose significant challenges for UK apple production. Nevertheless, new fundamental knowledge needed to develop more accurate chilling and heat accumulation models was generated, and this will help to inform climate change adaptation strategies so that potential impacts on the UK apple sector can be managed and mitigated more effectively.