Mapping Molecular Markers And QTL Controlling Agronomic Traits In Chinese Cabbage (B.rapa Ssp.pekinensis)

Chinese cabbage B. rapa ssp pekinesis), originated from China, belongs to the genus Brassica and is one of the most widely cultivated and consumed vegetables in China. As a genetic linkage map with high density of molecular markers is of practical importance in molecular marker assisted selection, QTL mapping and map based gene cloning, we finished the construction of a molecular genetic linkage map of Brassica rapa in this research. The genetic linkage map of Brassica rapa (2n=20) was constructed with AFLP (amplified fragment length polymorphism) and SSR (Simple Sequence Repeats) markers using an Fl-derived doubled-haploid (DH) population of 183 lines. This mapping population was developed by crossing a line Y177-12 and a line Y195-93 which were different from each other distinctly in maturity, heat tolerance, disease resistance, bolting, et al.AFLPs were generated by the using restriction enzymes EcoRI in combination with MseI. 34 primer combinations (PCs) were selected as the most informative ones from 326 E+2/M+3 combinations. Using these 34 primer pairs, a total of 245 markers were detected, which was 7.2 markers per primer pair. 23 primers were selected as the most informative ones from 138 primers.Software JoinMap 3.0 was used for linkage grouping and map construction. The resulted map contained 222 AFLP markers and 11 SSR markers covering a total distance of 1062 cM, corresponding to 4.56 cM per marker. Length of linkage groups varied from 23-177 cM, and the number of AFLP and SSR markers linked to each group ranged from 10-36 markers, corresponding to 2.3-7.89 cM per marker on each group.An AFLP and SSR genetic map with 233 markers and a DH population from the cross of two cultivated Chinese cabbage lines, were employed in mapping and analysis quantitative trait loci controlling traits related to head in Chinese cabbage, using composite interval mapping method. Forty-nine QTL, including one for head weight, three for leaf weight, six for 3 leaves weight, five for side weight, three for side/leaf, six for wide of leaf, seven for rib thick, six for number of head-forming leaves, three for head length, one for head diameter, four for head length/ head diameter ratio, two for tip high and two forfundus high.Leaf hair is one of the important biological traits in Chinese cabbage. By using an AFLP and SSR map constructed based on a DH population, we detected 2 QTLs for the trait. One has a LOD value of 128.1 and explaines 86.8% of the variation. The other has a LOD value of 5.48 and explaines 12.1% of the variation.