Fine-mapping And Cytological Mechanism Of A Seed Number Per Silique QTL-qSN.A7 In Rapeseed(Brassica Napus L.)

At present,the self-sufficiency rate of China's edible vegetable oil is less than 35%,which seriously threatens the supply security.Among the domestic vegetable oils,rapeseed oil accounts for more than 55%,and is the best quality edible oil.Therefore,the development of rapeseed production is the key to maintaining the safety of edible oil supply.At present,one of the main factors that restrict the rapeseed production in China is that the low per unit yield,which is urgently to be improved.Under the same planting density,the seed yield is dependent on the yield per plant,and the yield per plant is directly determined by the three components:the seeds number per silique,the siliques number of per plant,and the seed weight.The number of seeds per silique in rapeseed germplasm resources showed a large variation range?from serval to more than 30seeds?,which provided invaluable materials for the genetic and breeding research of this trait.At present,the regulatory genes and mechanisms for the natural variation of the SNPS are basically unclear.To this end,our group used the representative lines from rapeseed germplasm resources to conduct genetic and cytological analyses.We found that the natural variation of the SNPS was mainly determined by the maternal and embryonic genotype effects.We proposed the idea of decomposing the number of seeds per silique into the number of ovules per ovary,fertile ovule ratio,ovule fertilization rate and infertile ovule development rate and clarified their relative contributions.We also mapped two reproducible new QTLs that regulate the SNPS.Among them,the major QTL qSN.A6 has been mapped,and the BC₃F₁ near-isogenic line of qSN.A7 has also been constructed.On this basis,this study intends to perform a phenotypic test on non-recombinant individuals from the BC₃F₂ population to confirm the effect of qSN.A7.Then,the recombinant plants in the BC₄F₂ generation near-isogenic line were used to further fine-map qSN.A7.At last,the two types of homozygous near-isogenic lines for qSN.A7 were subject to genetic and cytological analyses to clarify its regulatory mechanism.The main results and conclusions obtained are as follows:1.The heterozygous individuals were screened from BC₃F₁ generation QTL near-isogenic lines,using the two markers?Niab043 and CNU339?flanking q SN.A7.After self-crossing,the BC₃F₂ seeds were obtained and planted.The SNPS of two types of homozygous individuals from BC₃F₂ population were investigated and compared,which showed a significant difference of 2.23.2.A total of 255 recombinant individuals were screened from a large of BC4F2 population of2551 individuals,using the two markers?Niab043 and CNU339?flanking qSN.A7.Subsequently,five specific and polymorphic molecular markers were developed in the target QTL interval?4.237Mb?to further genotype the recombinant individuals.Finally,the phenotypic data of seed number per silique of each recombination type was analyzed and compared,which delimited qSN.A7 to a smaller interval between Ni201 and BnID320?1.389 Mb?.3.To further clarify the regulatory mechanisms of qSN.A7,the two types of homozygous near-isogenic lines were used to genetic and cytological analyses.First,the two homozygous near-isogenic lines were used to perform the artificial self-and reciprocal cross experiments.The results showed that the difference in the SNPS between the two lines was determined by the embryonic genotypic effect.Then,we performed cytological observation on the number of initial ovules,ovule fertility and pollen fertility of two homozygous near-isogenic lines.The results showed that there was no significant difference in all of the three investigated indexes.The above experiments further confirmed that q SN.A7 was regulated by embryonic genotype,which is completely different from the known loci qSS.C9 and qSN.A6.The results can be used for molecular marker-assisted selection,and also lay a foundation for subsequent map-based cloning and mechanism analysis of qSN.A7.