The influence of autumn-winter temperatures on endodormancy release and blooming performance of apricot (Prunus armeniacaL.) in central Italy based on long-term observations

In the context of global warming, mild winter temperatures could compromise the fulfilment of the chilling requirement (CR) for overcoming flower bud endodormancy, impacting on the yields of perennial species such as apricot (Prunus armeniacaL.). Long-term and site-specific data on air temperatures allowed us to explore the influence of yearly chill accumulation on the endodormancy release of flower buds and blooming responses of two apricot cultivars ('San Castrese' and 'Orange Red') selected as models for their different characteristics such as geographical origin, CRs of flower buds, blooming time, and fruiting regularity. The CR for breaking flower bud endodormancy was determined by the 'forcing test', and the accumulation of chill temperatures was estimated using the Chilling Units (CUs) model. Since the 1990s, milder autumn-winter temperatures and a decline in CUs were recorded. These occurrences had consequences on the endodormancy release, influencing date, and intensity of blooming. 'San Castrese', although able to conform to warmer winters, showed the most significant changes in terms of blooming date delay, and reduction in blooming and fruiting intensity. Based on the irregular winter chilling locally verified over several years, serious alterations in apricot floral biology can be predicted.