Cytological Basis and Molecular Mechanism of Variation in Number of Seeds Per Pod in <italic>Brassica napus</italic>

The number of seeds per pod in Brassica napus shows great variation among different cultivars, lines and germplasm resources. Studies on this trait are important in increasing rapeseed yield by utilizing advantageous variations. In this study, we revealed the cytological basis and molecular mechanism of the formation of variation in number of seeds per pod in Brassica napus through analyzing a series of doubled haploid lines and cultivars. The results showed that a part of ovule primordiums could not develop into mature seeds because they had encountered abortion during the development process. The percentage of normally developed ovules was an important determinant of variation in number of seeds per pod. Cytological analyses concluded that the abortion of ovule occurred between the stages of megaspore degradation and uninucleate gametophyte. Our results also showed that the variation in the rate of ovule abortion is related to the differences in the regulation level of BRS-BRI1 signaling pathway in Brasica napus.