Phenological response of olive cultivars to inter-annual temperature variability in Morocco

Climatic factors strongly influence the phenology of olive trees, with flowering time responding sensitively to temperature variations. This study investigated the effects of inter-annual temperature variability on olive phenology in a mountainous Mediterranean region of Morocco. Experiments were conducted over two contrasting seasons (2020–2021 and 2021–2022) on four cultivars (Picholine Marocaine, Haouzia, Dahbia and Arbequina) in Khenifra. Forcing tests were performed to determine endodormancy release dates and to estimate chill and heat requirements. Throughout the dormancy period, fresh flower bud weights were recorded before and after a 7-day forcing period at weekly intervals and bud water content was monitored. The climatic requirements of each cultivar represent a major determinant of adaptability under variable seasonal conditions. The results revealed clear inter-cultivar differences in endodormancy and ecodormancy durations, thermal requirements and flowering dates. Arbequina exhibited the earliest dormancy release with relatively low chill requirements, whereas Picholine Marocaine and Dahbia flowered later and required higher chill accumulation. In all cultivars, bud growth activity increased near the time of dormancy release, indicated by water content exceeding 30 %, with only minor genotypic variation in the transition between dormancy phases. Across both seasons, flowering occurred after heat accumulation ranging from 6774 to 8051 Growing Degree Hours (GDH). These findings suggest that co-planting Picholine Marocaine and Dahbia may improve cross-pollination and enhance yield potential due to their similar flowering responses to seasonal temperature patterns. Overall, this research provides valuable insights for cultivar selection and orchard management under variable climatic conditions in Mediterranean environments.