Introgressing Genetic Variations Of Multiple Brassica Juncea Cultivars Into New-type Brassica Napus

Brassica napus is widely grown around the world as oil crop with narrower genetic basis.Though Brassica juncea has less planting area than B.napus,its drought tolerance and barrenness and different genome from B.napus.We have previously created a new-type B.napus gene pool with A^rA^rC^cC^c genomic components by large-scale interspecific crosses between 74 Brassica carinata and 122 Brassica rapa cultivars and recurrent selection.To further extend the genetic diversity of new-type B.napus materials,we intend to introgress B.juncea genomic components into these materials and thus develop a unique gene resource pool which contains B.rapa,B.carinata,B.napus and B.juncea genomic components.Our group have collected 371 B.juncea accessions from 8 countries.152 B.juncea accessions with yellow seeds,insect resistance,drought resistance and other superior traits were selected for interspecific crosses with 61 new-type B.napus inbred lines.We finally obtained 2427 F₁ hybrid plants and detect them via morphological and molecular marker approaches.The results showed that in 2017,413 F₁ plants were obtained from 101 hybrid combinations（B.juncea were used to be the male parent）,of which only 47 plants were identified to be true hybrids with the rate at 11.4%.In 2018 and 2019,2014 F₁ plants were obtained from 155 hybrid combinations（B.juncea were used to be the female parent）,of which 1868 plants were identified to be true hybrids with the rate at 92.8%.After three cross rounds,we totally obtained 256 hydrid combinations developed from 152 B.juncea and 61B.napus parent lines.270 pairs of SSR primers selected from 6347 pairs of B.juncea genomic（A^j）IP（Intron Polymorphism）primers and 16 pairs of new-type B.napus-specific SSR primers were used for polymorphic primer selection among B.juncea,new-type B.napus,B.rapa,Brassica olearacea and Brassica nigra mixture.Finally we obtained 95 pairs of primers to identify introgression from B.juncea.64 F₂ and 74 BC₁F₁ combinations were obtained from the above F₁population by self-crossing and backcrossing.Component introgression analysis was performed on 3 F₂ plants and 3 BC₁F₁ combinations with 36 selected pairs of primers.We found that B.juncea genomic content were over 50%in all crosses,of which the highest was 89.6%and the lowest was 54.0%.The average content was 72.8%closed to the expected level 75%.New traits such as yellow seeds,deep roots appeared and higher TW（Thousand seed weight）were observed in 3 representative crosses selected from above 6 crosses of F₂ and BC₁F₁.Further introgression analysis used above 36 pairs of primers to identify B.juncea genomic content for 79 selfcrossing progenies in 3 crosses of F₃ and BC₁F₂.The results showed that the variation range of B.juncea genomic content in the three combinations were3.7%-36.8%,3.7%-80.3%,and 14.8%-63.0%.Average content were 17.4%,58.6%,and38.2%,which were 56.8%,28.5%,and 15.8%lower than the BC₁F₁ and F₂ generations.The chromosome number results showed that most of plants genome was unstable in crosses of F₃ and BC₁F₂,but several plants’chromosome numbers were back to 38.This study laid foundation for further hybridization,selection and identification of new-type B.napus with 38 chromosomes.