Construction Of A Molecular Genetic Map And Mapping Of QTL Related To Main Agronomic Traits In Cabbage (Brassica Oleracea Var. Capitata)

Cabbage (Brassica oleracea var. capitata) originated in the regions from Mediterranean Sea to Northern Sea coast, is an important vegetable crop which widely cultivated in the world. Building a high density molecular genetic linkage map is meanful for QTL mapping, map based gene cloning and molecular marker assisted selection. A double-haploid (DH) population (D19) of 102 lines was obtained by microspore culture from the F₁ between two advanced inbred lines of 624 and 24-5 of cultivated cabbage. In this research, the genetic linkage map of Brassica oleracea var. capitata (2n=18) was constructed with AFLP (amplified fragment length polymorphism) marker and mapped QTL controlling main agronomical traits. The main results are as follows:(1) The isolated microspore of six genotypes of cabbage×cabbage were cultured in the NLN-13 liquid medium. It was found that genotypes had important impact on embryo formation. Three genotypes got a little high rate of embryo, though the other three genotypes could hardly produce embryo. Finally built a DH population (D19) by microspore culture from the F₁ between 624 and 24-5.(2) 87 primer combinations (PCs) were selected as the most informative ones from 512 AFLP combinations between the two parental lines. These selected PCs which used in DH lines produced 771 polymorphic markers, averaging 8.9 polymorphic markers per PC. Among 771 AFLP markers, 408 (52.9%) markers derived from the parent 624 and 363 (47.1%) markers derived from the parent 24-5, the majority of 771 markers showed 1:1 segregation ratio for two parental alleles. In addition, AFLP markers had a high ratios of distorted segregation, and 459 markers, 59.5% of 771, segregated distortedly at P<0.05, among which 165 (35.9%) markers deviated to 624 and 294 (64.1%) markers deviated to 24-5, which showed that DH population deviated to the genotype of 24-5.(3) Software JoinMap 3.0 was used for analyzing 771 polymorphic markers. A total of 458 markers were mapped into 8 linkage groups, covering 655 cM with an average interval distance of 1.23 cM between loci. The length of markers in every linkage group varied from 30cM to 151 cM, and the number of markers in linkage group ranged from 5 to 165,the average interval distance is from 0.92 cM to 6 cM. A total of 57.4% distorted markers distributed in the map, and linkage groups LG1, LG4 and LG7 might have segregation distortion regions in these linkage groups in which the markers most or a half of them were distorted markers. The molecular genetic map is the first high density map built by DH population of cabbage in the world.Map QTL 4.0 software and multiple QTL model method were employed in mapping and analyzing quantitative trait loci (QTL) controlling 37 main agronomical traits in cabbage. 11 QTL related to 11 agronomic traits in 6 linkage groups were detected. 6 QTL controlled the characteristics of plant spreading, the largest outer leaf length, the outer leaf shape, plant shape, petiole length and outer leaf vein respectively, and each contributed 10.3%, 9.9%, 9.8%, 9.3%, 8.7% and 8.6% individually. 5 QTL controlled the characteristics of hape of head, head texture, basic stem length, internal color of head and head height and each contributed 11.9%, 8.8%, 9.2%, 9.9%, 8.4% individually.