Analysis Of Population Structure And Construction Of Genetic Linkage Map In Non-heading Chinese Cabbage

Brassica campestris (syn. rapa) is an important vegetable and oil crop in Brassica genus, in which non-heading Chinese cabbage is one of main vegetable crops cultivated and consumed in China. Much variation for phenotypic traits is existed in the cultivated group of non-heading Chinese cabbage, it is necessary to explore the variation characteristics and genetic basis at the molecular level. In this present thesis the population structure of the non-heading Chinese cabbage accessions collected in the market was assessed to provide scientific theories for their genetic variation, excellent varieties breeding, germplasm utilization reasonably and cultivar group classification. Furthermore, it will be useful for performing association mapping, mapping targeted traits and discovering new genes base on the natural variation of the non-heading Chinese cabbage population. Using one doubled haploid (DH) permanent mapping population, the genetic map of B. campestris was constructed by adding new markers of SSRs and SRAPs combined with previous AFLP data. It will be useful for mapping and cloning of targeted genes and breeding in markers assisted selection. The results are as follows:1. Using non-heading Chinese cabbage genome DNA as template, the suitable SRAP reaction system for non-heading Chinese cabbage was optimized and established by orthogonal design with five factors and four levels involving Mg2+, dNTPs, Taq DNA polymerase, primers and template DNA.2. Fifty six markers from 21 SSRs were imported in the program Structure to identify subpopulations, resulting in 4 subgroups (S1, S2, S3 and S4) in the 78 accessions of non-heading Chinese cabbage. Subpopulation S1 included 34 Pak choi, one Caixin and 2 Wutacai accessions with both origins of southern and northern parts;Subpopulation S2 had pure genetic background with only Pak choi accessions riginated mostly from northern part; Subpopulation S3 included 5 Pak choi, 3 Caixin and 3 Chinese cabbage accessions; Subpopulation S4 included 6 Pak choi, 5 Chinese cabbage, 2 Caixin and 2 Wutacai accessions.3. Fifty six markers from 21 SSRs were used in UPGMA clustering analysis, resulting in 3 groups in the collected accessions, in which groupâ… included 3 subgroups. The accessions in subgroupâ… -1 andâ… -2 and were mainly distributed in structure subpopulation S1, and theâ… -3 subgroup was similar to structure subpopulation S2, the groupâ…¡was similar to structure subpopulation S4, the groupâ…¢was similar to structure subpopulation S3.4. Combining with previous AFLP data, the linkage analysis of a doubled haploid (DH) population was performed by software Joinmap 3.0. A genetic map of B. campestris with 10 linkage groups was obtained, in which 335 AFLPs, 7 SRAPs and 45 SSRs and one flowering time specific marker BrFLC2 were distributed on each linkage group respectively. The total length of this linkage group was 669.8 cM with 1.9 cM of average distance. The length of 10 linkage groups was ranged from 30.2cM to 90.5 cM. Fifteen out of 28 molymorphic SSR were mapped on the genetic map and distributed in 8 linkage groups except for A05 and A07; seven SRAP markers were distributed in 5 linakge groups A02, A04, A06, A08 and A10; one flowering time-specific gene FLC2 was mapped on the top of linakge goroup A02.