Phenological response of olive cultivars to climate variation in Morocco

Climatic factors strongly influence the phenology of olive trees. The timing of flowering, in particular, responds strongly to climatic drivers, most notably to variation in temperature. To gain insights into prospective impacts of climate change, which is projected to generate decreases in winter chill as well as increases in spring heat, we assess the response of olive trees to temperature variation. To date, few studies have focused on assessing floral bud dormancy and growth dynamics of olive in mild cropping areas such as Morocco. Experiments were conducted during two seasons, 2020–2021 and 2021–2022, on four olive cultivars (Picholine Marocaine, Haouzia, Dahbia and Arbequina) in Khenifra, Morocco. We used forcing tests to determine the endodormancy release dates and to estimate chill and heat requirements. Throughout the trees’ dormancy period, we measured fresh flower bud weights before and after a forcing period of 7 days in a growing room at 7-day intervals. Climatic requirements are a major determinant of a cultivar’s ability to thrive under future climate conditions. Our findings demonstrated differences among the studied olive cultivars in terms of endodormancy and ecodormancy durations, chill and heat requirements and flowering dates. The cultivar Arbequina showed an early date of endodormancy release, with low chill requirements. Picholine Marocaine and Dahbia showed late flowering dates, related to relatively high chill requirements. For all cultivars, effective bud growth activity started around the date of endodormancy release or a few days later, as indicated by the water content in floral buds exceeding 30%, with little genotypic variation in the process of transition from the endodormancy to the ecodormancy phase. For all cultivars over the two years, flowering occurred after an average heat accumulation of between 6,774 and 8,051 GDH. This study demonstrated that cultivating and growing Picholine Marocaine and Dahbia together in the same orchard could be a potentially efficient way to improve cross-pollination, productivity and yield of olives. This combination showed relatively similar phenological behavior in terms of flowering time in response to temperature variation.