Modeling Dormancy for Changing Crop Suitability

The minimum winter temperatures and lack of in-season heat that limit the northern distribution of sweet cherry production have changed sufficiently over the past five decades to allow northward and upslope expansion of growing areas in British Columbia, Canada. There is considerable interest in projecting changing crop suitability into the future and we have combined a series of dormancy, cold hardiness, phenology and in season fruit growth models for sweet cherry to explore changing locations for sweet cherry production. A key component of this process is the use of temperature driven models for dormancy induction, completion of endodormancy and ecodormancy. We compare various methods of computing chilling and forcing (heating) temperatures tested for ‘Lapins’ and ‘Sweetheart’ sweet cherry cultivars using bud sticks sampled from the field over the fall and winter and forced in the greenhouse and in- field samples over 6 years. Observations in the greenhouse of flower quality (broken buds continue to develop up to bloom) and the percentage of flower buds which break indicate that endodormancy completion is not adequately described by a single chill value. This has been demonstrated in chill overlap models in which chilling and forcing together contribute to the success of broken buds after initial chilling requirements have been met. A study of the underlying molecular mechanisms has been initiated with RNA-Seq libraries detailing gene expression across the entire winter season. In addition to identifying temporal markers that correspond to dormancy transitions there is also a striking drop in expression of specific cell cycle regulators (cyclins and cyclin dependent kinases) which persists after initial chilling requirements are met.