Delineating chilling and forcing periods is one of the challenging topics in understanding how temperatures drive the timing of budburst and bloom in fruit tree species. Here, we investigated this question on olive trees, using flowering data collected over six years on 331 cultivars in the worldwide collection of Marrakech, Morocco. Using a Partial Least Squares approach on a long-term phenology (29 years) of ‘Picholine Marocaine’ cultivar, we showed that the relevance of delineating the chilling and forcing periods depends more on the variability of inter-annual temperatures than on the long-term datasets. In fact, chilling and forcing periods are similar between those delineated by using datasets of 29 years and those of only 6 years (2014–2019). We demonstrated that the variability of inter-annual temperatures is the main factor explaining this pattern. We then used the datasets of six years to assess the chill and heat requirements of 285 cultivars. We classified Mediterranean olive cultivars into four groups according to their chill requirements. Our results, using the Kriging interpolation method, indicated that flowering dates of most of these cultivars (92%) were governed by both chilling and forcing temperatures. Our investigations provided first insights to select adapted cultivars to global warming.

Flowering date in perennial fruit trees is an important trait for fruit production. Depending on the winter and spring temperatures, flowering of olive may be advanced, delayed, or even suppressed. Deciphering the genetic control of flowering date is thus key to help selecting cultivars better adapted to the current climate context. Here, we investigated the genetic determinism of full flowering date stage in cultivated olive based on capture sequencing data of 318 genotypes from the worldwide olive germplasm bank of Marrakech, Morocco. The genetic structure of this collection was organized in three clusters that were broadly attributed to eastern, central, and western Mediterranean regions, based on the presumed origin of genotypes. Flowering dates, collected over 7 years, were used to estimate the genotypic best linear unbiased predictors, which were then analyzed in a genome-wide association study. Loci with small effects were significantly associated with the studied trait, by either a single- or a multi-locus approach. The three most robust loci were located on chromosomes 01 and 04, and on a scaffold, and explained 7.1%, 6.2%, and 6.5% of the trait variance, respectively. A significantly higher accuracy in the best linear unbiased predictors of flowering date prediction was reported with Ridge- compared to LASSO-based genomic prediction model. Along with genomic association results, this suggests a complex polygenic determinism of flowering date, as seen in many other fruit perennials. These results and the screening of associated regions for candidate genes open perspectives for further studies and breeding programs targeting flowering date.

Delineating chilling and forcing periods is one of the challenging topics in understanding how temperatures drive the timing of budburst and bloom in fruit tree species. Here, we investigated this question on olive trees, using flowering data collected over six years on 331 cultivars in the worldwide collection of Marrakech, Morocco. Using a Partial Least Squares approach on a long-term phenology (29 years) of ‘Picholine Marocaine’ cultivar, we showed that the relevance of delineating the chilling and forcing periods depends more on the variability of inter-annual temperatures than on the long-term datasets. In fact, chilling and forcing periods are similar between those delineated by using datasets of 29 years and those of only 6 years (2014–2019). We demonstrated that the variability of inter-annual temperatures is the main factor explaining this pattern. We then used the datasets of six years to assess the chill and heat requirements of 285 cultivars. We classified Mediterranean olive cultivars into four groups according to their chill requirements. Our results, using the Kriging interpolation method, indicated that flowering dates of most of these cultivars (92%) were governed by both chilling and forcing temperatures. Our investigations provided first insights to select adapted cultivars to global warming.

Understanding intraspecific functional trait variability (ITV) is crucial for elucidating plant functional strategies under environmental change. This study investigates the functional responses of 129 Mediterranean olive (Olea europaea L.) cultivars conserved in the Worldwide Olive Germplasm Bank of Marrakech (WOGBM), focusing on three key leaf traits: specific leaf area (SLA), specific leaf water content (SLWC), and leaf area (LA). Substantial ITV was observed, with variability predominantly driven by cultivar differences and geographic origin. LA accounted for the highest within-cultivar variability (43.60%), followed by SLWC (31.67%) and SLA (17.92%). Geographic origin significantly influenced trait expression, with eastern Mediterranean cultivars exhibiting conservative resource-use strategies (high SLWC, low SLA, and LA), while western cultivars displayed acquisitive strategies (high SLA and LA, low SLWC). Principal component analysis further differentiated eastern and western cultivars, reflecting biogeographical and evolutionary influences. The relationship between LA and climatic variables suggests climate-driven selection, where cultivars from wetter regions develop larger leaves to optimize light capture and carbon assimilation, whereas those from drier environments exhibit smaller leaves to reduce water loss. These findings highlight a trade-off between resource acquisition and conservation, supporting the leaf economic spectrum at the intraspecific level. This study underscores the importance of ITV in olive diversification and adaptation, providing insights for breeding, conservation, and climate resilience. A trait-based approach proves valuable for exploring domestication processes and plant responses to environmental gradients.

Background Future climate models project severe impacts on flowering phenology of perennial fruit trees in the Mediterranean region under increasing global warming, including the olive tree, a key species extensively cultivated in the region. Thus, understanding the genetic factors regulating flowering is crucial for providing knowledge to select suitable cultivars and designing future olive breeding programs. Here, we aimed to investigate the genetic control of full flowering date (FFD) through Quantitative Trait Loci (QTL) mapping approach. Two high-density parental genetic maps, with more than 10k SNPs, were constructed based on an “Olivière” x “Arbequina” F1 hybrid progeny. Phenological observations of the same progeny were conducted across five environments (site × season), and data served to compute Best Linear Unbiased Predictors (BLUPs) for FFD. Both FFD-based BLUPs and single-environment data were used to detect key QTLs, which were further explored through in-silico candidate genes investigation. Results Analysis of FFD distribution highlighted a high heritability with transgressive segregation. A total of 18 significant QTLs were identified in BLUPs analysis, and six were selected as the most relevant. Two QTLs were co-detected on the same linkage groups (LGs) of both parental genetic maps in BLUPs and some environments: LG09 (qFDO9b/ qFDA9) and LG07 (qFDO7/ qFDA7). Additionally, four QTLs on LG3 (qFDA3), LG22 (qFDA22) and LG13 (qFDA13) on “Arbequina” map, and LG13 (qFDO13) on “Olivière” map were revealed in BLUPs as well as in some single-environment analyses. Both qFDA13 and qFDA22 were characterized both by higher explained variance (14.6% and 11.6%, respectively) and additive values (-1.09 and + 1.15, respectively). Candidate genes investigation revealed genes within key QTLs probably involved in transcription regulation, including WRKY71, RLT3, and ABSCISIC ACID-INSENSITIVE-5-LIKE, in addition to a transport protein: FT–INTERACTING protein1. Genes highlighted were shown to interact with main flowering date regulators such as FLOWERING LOCUS T (FT) and FLOWERING LOCUS C (FLC). Conclusion Our study aimed to highlight the genetic control of the flowering date in the olive tree. The genomic regions covered by the detected QTLs and the candidate genes identified represent valuable resources for further investigations through genome-wide association and functional genomics studies. These findings will provide key information for applying genomic selection to develop new varieties more adapted to future climate projections.