Adaptation of sweet cherry and apple phenology to temperature variability in Moroccan orchards using forcing tests and chill models

Rising temperatures in the Mediterranean region threaten fruit trees with high chill requirements, such as sweet cherry and apple by reducing winter chill accumulation, altering phenology and increasing production irregularity. Quantifying cultivar chill/heat requirements is therefore essential to identify cultivars adapted to a particular climate. To assess cultivar adaptation potential by determining the endodormancy release dates and their specific agroclimatic requirements, forcing tests were conducted over three consecutive seasons (2020–2023) on ten sweet cherry and two apple cultivars grown at two major fruit-producing regions in Morocco (Azrou and Imouzzer-Kandar). In addition, the impact of temperature variations on flowering and fruit set rates was evaluated. The results revealed major differences in the dynamic endodormancy release and chill/heat requirements among the studied species/cultivars, these requirements ranged between 662–929 Chill Hours (CH), 432–954 Chill Units (CU), 26.7–56.5 Chill Portions (CP) and 8180–10048 Growing Degree Hours (GDH) for sweet cherry and between 986–1025 CH, 1025–1052 CU, 59.3–61.4 CP and 6982–8617 GDH for apple. Based on these responses, sweet cherry cultivars were classified into three groups: i) low-chill cultivars with variable flowering and reproductive performances, ii) high-chill cultivars with late-flowering and high fruit set and iii) cultivars with balanced chill requirements and moderate flowering performances. In apple, Gala outperformed Top Red in reproductive efficiency. Finally, colder site such Azrou promoted flowering but reduced fruit set, whereas milder Imouzzer-Kandar enhanced vegetative growth and fruit set. Our results provided practical decision support for cultivar selection and site-specific orchard planning under ongoing climate warming.