Declining chilling and its impact on temperate perennial crops

This paper examines the impacts of declining winter chill on the production of temperate perennial crops in the northern hemisphere. Recent studies have linked long-term climate data to key seasonal reproductive events in perennial plants. These studies suggest that the amount of winter chill occurring in the UK has declined and is predicted to continue to do so, based on future climate change scenarios described in the UK Climate Impacts Programme. It is apparent that there is a serious lack of mechanistic understanding of the physiological, molecular and genetical basis of winter chill requirement and dormancy-related environmental factors which affect perennial crop growth and yield. This situation exists despite knowledge of the impacts of climate on perennial plant development and an ability to model its effects, for many temperate fruit crops, on yield. The implications for future reductions in winter chill require recognition as a potential limiting factor on fruit production across Europe, particularly in the south. Within this review we describe the symptoms of lack of winter chill; these include effects on bud break, flower quality and the potential to set fruit, as well as effects on vegetative growth and development. Also included is current knowledge of developmental and physiological events which link flower initiation, anthesis, dormancy, chilling and bud break. Attention is given to what is known about dormancy induction, satisfaction of specific requirements and bud break. Possible strategies are described for mitigation of reduced winter chill, providing long-term solutions to secure perennial fruit supplies in Europe. This includes exploiting genotypic variability, within several perennial crops, through plant breeding to develop low chill-cultivars, together with opportunities to change crop management practices and growing systems to tolerate low chill.