Development And Genetic Diversity Analysis Of New-Type Brassica Juncea

B. juncea derived from hybridization between B. rapa(AA) and B. nigra(BB), followed by chromosome doubling. Due to the relative short domestication history, the genetic basis of B. juncea was narrow compared with its parental species. Resynthesized B. juncea by crossing B. rapa with B. nigra is the main way to enlarged germplsm of B. juncea. However, the process of resynthesizing B. juncea was a low effective since it need to embryo rescue to obtain hybrid breeding due to cross-compatibility barrier. Here, a hexaploid strategy was proposed that hybridization was first developed by crossing B. juncea with B. rapa or B. nigra via embryo rescue and chromosome doubling to obtain hexaploid(AAAABB or AABBBB), respectively. And then the hybridizations between hexaploid and parental species(AAAABB × BB, AABBBB × AA) were performed to develop new B. juncea, where the genetic components of B.nigra and B.rapa were introduced into B. juncea. The results were shown below. 1 Development of hexaploidIn this study, 7 B. juncea lines as female were crossed with 4 lines of B. nigra and 3 lines of B. rapa, respectively. The embryos of 4 combinations germinated and were cloned via embryo rescue and chromosome doubling. All of them were identified as hexaploids by checking morphological characterizations, pollen fertility, cytology analysis and molecular markers, including 1 AABBBB and 3 AAAABB.No significant differences(p > 0.05) were found between two types hexaploid AAAABB and AABBBB for seed set in hexaploid S0, but significant differences(p < 0.01)were found in S1. 2 Development of new-type B. junceaNew-type B. juncea were developed by crossing hexaploid with B. nigra or B. rapa, i.e. AAAABB × BB, AABBBB × AA. The crossability of AAAABB × BB and AABBBB × AA was 0.048 and 0.037 seed/pod, respectively, without significant difference between the two cross patterns(p > 0.05). The data indicate that the new-type B. juncea can be developed by both cross patterns(AAAABB × BB and AABBBB × AA). 3 Analysis of genetic basis of the new-type B. junceaIt was showed that, the genetic distance within the new-type B. juncea(0.37 ± 0.16) was bigger than that within the natural B. juncea(0.25 ± 0.08) and among the new-type and natural B. juncea(0.28 ± 0.11). The genetic diversity of the new-type B.juncea(0.36 ± 0.14)was also bigger than that of natural B. juncea(0.30 ± 0.15). The principle analysis separated the new-type and natural B. juncea and reveled wide genetic diversity in new-type accessions.The above data suggested that, as compared with traditional methods, the hexaploidy strategy could transfer the genetic components from B. rapa and B. nigra into B. juncea in a relative easier manner and thus broaden the genetic basis of the B. juncea.