Cytological and genetic analyses of the seed number per silique locus BnSNSC09 in Brassica napus.

Key message: The rapeseed material 'DH46' had an extremely low-SNS phenotype due to multiple megaspore mother cells in ovules. A novel SNS-related locus was mapped to a 169-kb interval on chromosome C09. Seed number per silique (SNS) is a yield-related trait in rapeseed (Brassica napus). Although numerous quantitative trait loci associated with SNS have been identified in diverse rapeseed populations, the primary loci and genetic basis underlying SNS variation remain poorly understood. In this study, an extremely low-SNS material named 'DH46' was employed to investigate the genetic locus associated with SNS. Cytological studies revealed that the reduced SNS phenotype is attributable to the presence of multiple megaspore mother cells within the ovules. To dissect the genetic control of this trait, a BC₃F₄ population developed from the cross of 'DH46' and the cultivar 'ZS11' was analyzed, and a major locus BnSNSC09 acting as a semi-dominant factor associated with SNS was identified. Fine mapping in the BC₃F₆ population narrowed the causal region to a 169-kb interval on chromosome C09. Candidate gene analysis revealed that BnaC09G0288500ZS, which exhibits variants in promoter and coding sequences, was the most promising candidate gene for BnSNSC09. These findings establish a robust foundation for cytological investigations and genetic analyses of the low-SNS mutant 'DH46,' with the ultimate goal of preventing ovule abortion and enhancing SNS to develop higher-yielding rapeseed varieties.