| A molecular genetic map for Chinese cabbage was constructed based on AFLP, RAPD and SSR markers using DNA samples extracted from a doubled haploid (DH) population obtained through microspore culture from the F1 between two homozygous parents: 91-112 and T12-19. QTLs analysis of Chinese cabbage resistance to TuMV was also carried out. The main results are as follows:⑴ The efficiency of different molecular markers used in construction of genetic map was evaluated. 20 polymorphic primer pairs with clear and repetitive amplification were obatined by screening 64 AFLP primer combinations, and an average of 13.2 polymorphic bands were observed from each AFLP primer combination. 6 pairs of polymorphic primers were selected out from 15 SSR primer pairs, which produced 17 polymorphic bands totally, and each primer produced 2.8 polymorphic bands on average. 99 RAPD primers showed polymorphism between two parents among 500 primers, 150 polymorphic loci were obtained with an average of 1.5 polymorphic loci per primer. It can be concluded that the detection efficiency of polymorphic bands per primer is AFLP> SSR>RAPD.⑵ By the analysis of total 430 molecular markers including 263 AFLP markers, 150 RAPD markers and 17 SSR markers, one morphological marker and one SCAR marker with software JoinMap 3.0, a total of 360 markers(235 AFLP markers, 129 RAPD markers, 10 SSR markers, 1 SCAR marker and 1 morphological marker) were mapped to 10 linkage groups, covering 809.1cMwith an average distance of 2.2 cM between loci. The number of markers in every linkage group varied from 7 to 91, and the length is from 26.4cM to 145.9cM. ⑶ Further investigation on the source of markers from two parents was carried out. Among 235 AFLP markers used in map construction, 144(61.3%) markers derived from parent 91-112, and 91(38.7%) from another parent T12-19. More AFLP markers derived from the parent 91-112. In 10 SSR markers, there were 6 coming from 91-112 and occupied 60%, the markers from T12-19 occupied 40%. It was thus clear that SSR markers were also mainly from 91-112. In RAPD amplification, markers derived from 91-112 and T12-19 were 65 and 64 respectively, the proportion is almost equal. Among the total of 376 markers included in 10 linkage map, 215 (57.2%) markers derived from 91-112, 160 (42.8%)ones from T12-19. The proportion from the two lines remained balance basically. ⑷ There were different ratios of skewed segregation in DH population with different genetic markers. In 10 linkage groups, there exsisted a total of 149 skewed markers which accounted for 39.8%. Approximately 25.9% and 13.9% of the marker loci showed segregation deviating from the Mendelian ratios at the level of 0.01and 0.05 respectively. There were 97 skewed markers with AFLP technique occupying 42.2% of total AFLP markers, among which 52 markers deviated to 91-112 and accounted for 53.6%, 45 ones deviating to T12-19 occupied 46.4%. Therefore there was a tendency toward 91-112. The ratio of skewed segregation in SSR markers was 29.4%, among which 40% markers deviated to 91-112. 47(33.3%) RAPD markers showed skewed segregation in DH population, among them, 18 deviated to 91-112, others to T12-19. Therefore, skewed markers produced by RAPD and SSR mainly came from T12-19. Among the 149 markers deviated from Mendelian segregation ratios, 72 markers skewed to 91-112 and 77 skewed to T12-19 accounting for 48.3% and 51.7% respectively. The proportion was almost identical. ⑸ 4 QTLs controlling TuMV-C4 resistance at artificial inoculation andfield condition were identified with JoinMap 3.0 software and Interval Mapping method. 2 QTLs named Tu1 and Tu2 identified to be related to TuMV resistance at seedling stage in greenhouse by artificial inoculation. One was located on linkage group LG5a with the explanation of 61.0% variation. When Tu1 had the same genotype with 91-112, the disease index decreased 10.61 with additive effect. Tu2 was located on LG9, it could explain 14.7% of the variation. And when it had the same genot...
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