Background: Brassica napus is one of the most important oilseed crops, and also an important biofuel plant due to its low air pollution and renewability. Growth period are important traits that affect yield and are crucial for its adaptation to different environments in B. napus. Results: To elucidate the genetic basis of growth period traits, genome-wide association analysis (GWAS) and linkage mapping were employed to detect the quantitative trait loci (QTL) for days to initial flowering (DIF), days to final flowering (DFF), flowering period (FP), maturity time (MT), and whole growth period (GP). A total of 146 SNPs were identified by association mapping, and 83 QTLs were identified by linkage mapping using the RIL population. Among these QTLs, 19 were pleiotropic SNPs related to multiple traits, and six (q18DFF.A03-2, q18MT.A03-2, q17DFF.A05-1, q18FP.C04, q17DIF.C05 and q17GP.C09) were consistently detected using both mapping methods. Additionally, we performed RNA sequencing to analyze the differential expression of gene (DEG) transcripts between early- and late-flowering lines selected from the RIL population, and the DEGs were integrated with association mapping and linkage analysis to confirm their roles in the growth period. Consequently, 12 candidate genes associated with growth period traits were identified in B. napus. Among these genes, seven have polymorphic sites in the coding sequence and the upstream 2-kb sequence based on the resequencing data. The haplotype BnaSOC1.A05-Haplb and BnaLNK2.C06-Hapla showed more favorable phenotypic traits. Conclusions: The candidate genes identified in this study will contribute to our genetic understanding of growth period traits and can be used as targets for target mutations or marker-assisted breeding for rapeseed adapted to different environments.

Plant architecture optimization is central to high-yield crop breeding. The number of branches in Brassica napus (B. napus) determines canopy structure, light use efficiency, and yield. The transcription factor BRANCHED1 (BRC1) integrates multiple signals to negatively regulate branching. This study characterized five BnaBRC1 homologs in B. napus via bioinformatics, expression profiling, and CRISPR/Cas9 editing. All BnaBRC1s contain a conserved TCP domain, and their promoters are enriched with light-responsive and hormone-responsive cis-acting elements. BnaA01.BRC1 is highly expressed in leaves, stem nodes, roots, and siliques, and its transcription is coordinately regulated by low light, sucrose, and exogenous cytokinin, and gibberellin (GA) signals. Functional analysis showed that overexpression of BnaA01.BRC1 suppressed branching, whereas CRISPR/Cas9-mediated knockout of BnaBRC1 substantially increased branch number. In basal axillary buds, high BnaBRC1 expression was accompanied by upregulation of GA-inactivating GIBBERELLIN 2 OXIDASEs and the GA signaling negative regulator SPINDLY, and no direct interaction was detected between BnaA01.BRC1 and DELLA proteins, suggesting indirect regulation of branching via GA homeostasis. Collectively, this study demonstrates the pivotal role of BnaA01.BRC1 in branching regulation and provides a genetic resource and theoretical basis for plant architecture optimization and multi-branch germplasm innovation in B. napus.