A Genetic Linkage Map Of Chinese Cabbage Based On AFLP Markers Using DH Population

A genetic linkage map of Brassica rapa was constructed with AFLP (amplified fragment length polymorphism) markers using an Fl-derived doubled-haploid (DH) population of 59 lines. This mapping population was developed by crossing a low self-compatibility (SC) variety Bianzao-26 and high SC line Guang90E16 which were different from each other distinctly in maturity, heat tolerance, disease resistance, bolting, et al. The results were as follows.1. A modified CTAB was developed to isolate DNA of Chinese cabbage from each line and parents. Main bands of DNA were very clear with no degenetation, and the DNA concentration of each line and parents was even varying between 40~60ng/ u 1. The molecular weight of DNA was about 50Kb, which was consistent with A DNA. The sene of DNA after preamplification isolated in 1% agrose presented very clear smears with the size between 100~600bp. The qulity of DNA extracted in the study was adequately satisfactory for AFLP analysis.2. AFLPs were generated by using restriction enzyme EcoRI in combination with Msel. 83 primer combinations (PCs) were selected as the most informative ones from 256 E+3/M+3 combinations. These selected PCs produced 482 polymorphic bands between the two parental lines, averaging 5.8 polymorphic markers per PC. Using 62 primer pairs, a total of 426 markers were detected, which was 6.9 markers per primer pair. Among 426 AFLP markers, 125 markers were Bianzao-26-specific and 110 markers were Guang90E16-specific, and 40 markers showed codominance. The majority of 426 markers showed 1:1 segregation ratio for two parental alleles, and 210 AFLP markers, 49.3% of 426, segregated distortedly at P ^0.05, among which 127 markers were Bianzao-26-specific and 83 markers were Guang90E16-specific.3. Software JoinMap 3.0 was used for linkage grouping and map construction. The resulted map contained 346 AFLP markers covering a total distance of 708 cM, corresponding to 2.0 cM per marker. Length of linkage groups varied from 39 to 105 cM, and the number of AFLP markers linked to each group ranged from 9 to 87 cM, corresponding to 1.2-4.33 cM per marker on each group. 152 distorted markers could be grouped 6 SDRs (segregation distortion regions), which covered 35.8% of the totallinkage distance.4. Software GGT was applied to analyze genotypes of DH population. The result showed that linkage distances from Bianzao26 averaged 50.09%, while those from Guang90E16 averaged 45.92%.