Unraveling the genetic basis of full flowering date in olive tree through QTL mapping approach: Towards climate-adaptive breeding

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.