Genetic Architecture And Mechanism Of Seed Number Per Pod In Rapeseed(Brassica Napus L.)

Seed number per pod(SNPP) is one of the major components of yield, and is a target trait of breeding in rapeseed(Brassica napus L.). In the world, the SNPP of rapeseed shows great variation(from about 5 to 35 seeds per pod) in all rapeseed germplasms, which is invaluable for genetic improvement. However, the mechanism of SNPP variation in rapeseed is still ambiguity. In this study, we concluded that the major reasons for the variation of SNPP in rapeseed were embryo sac fertility and embryogenesis, which were controlled by maternal genotype and embryo genotype, respectively. While, offspring groups were derived from two parent materials(include in the above lines), as an example, systematic approach(genetics, cytology, and molecular level) to dissecting the abortion of embryo sac was the one of the reason leading to the low SNPP.The main results were described as follows:1. The SNPP variation in rapeseed was mainly caused by the abortion of embryo sac and thedevelopment of embryogenesis, followed by changes in the external environment, and pollenfertility of its impact is minimal(fertile material);2. The SNPP variation in rapeseed was mainly controlled by maternal genotype and embryogenotype, and a little cytoplasmic effects;3. We identified a common new major QTL on A06 linkage group via linkage mapping of F2/F2:3and RIL populations. While it failed to be validated by GWAS for a rare allele;4. By integrating our detected QTLs and association signals with the previous studies based onthe recently completed physical map of rapeseed, we obtain a complex genetic architecture ofSNPP that includes several major QTLs and numerous small-effect QTLs with underlyingcandidate genes. This was a solid foundation for the further study of SNPP in rapeseed;5. The identif ied major QTL qSN.A6 was fine-mapping by the NIL strategy from a preliminaryinterval of 1910 kb to final 88 kb, which was contained only 19 ORFs;6. The abortion of embryo sac was the major reason for the variation on qSN.A6.7. To our knowledge, this study is the first clearly demonstrates the genetic causation of trade-offamong SNPP and seed weight(SW) on single site, and speculated that this type ofantagonistic pleiotropy was due to a physiological interaction in which SNPP acts upstream ofSW;8. As expected, NIL(ZS11) out-yielded increased by 17.4% per plant. Thus, our results indicatethat qSN.A6 is an elite allele for rapeseed yield potential through the increase of SNPP.