| Broccoli (Brassica oleracea var. italica) is one of Brassica vegetable crops which head in food-based, and has important economic value and nutritional value. At present, there is higher request for the appearance quality traits of head among the export and domestic market. Breeding of the good head color, pleasing in appearance, and the round ball is the preferred and important goal in the broccoli breeding of new varieties, and whether there is head-leaf, green color depth and uniformity of the head, hollow bulbs and so on mainly affect the appearance quality of broccoli head. At present, selecting the traits is using the general breeding means or accordanced with mature head phenotypic characteristics in the field selecting, but long cycle and not in high efficiency. At present, these traits and related genes in the genetic study of molecular markers has not been reported. Researching the inheritance of these traits, building a high density molecular genetic linkage map and mapping QTL controlling important head quality traits, which expecting to provide theory guidance in order to acceleration the breeding process of broccoli.The two kinds of mixed major gene plus polygene inheritance models were used to analyze the inheritance of head-leaf,head-color and head-stem hole traits in the Brassica oleracea var. italica based on DH population and six generations materials obtained from a broccoli combination of 86101 plus 90196; constructed the molecular genetic linkage map with SSR markers using the DH population; and mapping QTL controlling the head-leaf,head-color and head-stem hole traits. The main results were as follows:(1)Six generations materials (P1,P2,F1,B1,B2 and F2) and a double-haploid (DH) population including 176 lines were obtained from the cross of two advanced lines 86101 and 90196 of broccoli through sexual hybridization and microspore culture.(2)The two kinds of mixed major gene plus polygene inheritance models were used to analyze the inheritance of important head quality traits in the Brassica oleracea var. italica based on DH population and six generations materials obtained from a broccoli combination of 86101 plus 90196. The results showed that: studied with doubled haploid (DH) population and the result indicated that the head-leaf trait was controlled by two major gene plus polygene (E-2-0 model), in addition, the two major gene had linkage inheritance, and also had additive and epitasis effects, the major gene heritability was 70.80%; the head-color trait was controlled by three additive-epitasis major gene plus additive-epitasis polygene (G-0 model), the major gene heritability was 93.38%; the head-stem hole trait was controlled by three additive major gene plus polygene, the major gene heritability was 84.62%. Studied with joint analysis of six generations (P1,P2,F1,B1,B2 and F2) and the result indicated that the head-leaf trait was controlled by two additive-dominant-epitasis major gene plus additive-dominant-epitasis polygene (E model), the major gene heritability in B1,B2 and F2 were 73.59%,57.70% and 87.07% respectively; the head-color trait was controlled by two additive-dominant-epitasis major gene plus additive-dominant- epitasis polygene (E model), the major gene heritability in B1,B2 and F2 were 83.13%,96.67% and 98.34% respectively; the head-stem hole trait was controlled by one additive-dominant major gene plus additive-dominant-epitasis polygene(D-0), the major gene heritability in B1,B2 and F2 were 48.33%,70.91% and 75.00% respectively.(3)Using the 1416 pairs of SSR primers to screened the parents and F1, detected 429 pairs of primers could be amplified clearly discernible banding pattern, of which 210 pairs of primers to detect polymorphism between the parents, resulting in 735 polymorphic markers, with an average of 3.5 / primer. The 210 pairs of primers used for polymorphism testing DH groups, there were 124 pairs of primers amplified by the DH groups with clear rules, good performance, which could be used in the construction of linkage groups. Among the 176 DH lines, statistic the gene type of 124 markers. It showed that 56.10% derived from the parent 90196 and 43.90% derived from the parent 86101, which formed 1:1 segregation ratio for two parental alleles, it showed that the DH lines had no segregation distortion.(4)The software Joinmap4.0 was used for linkage analysis with polymorphic markers of 124 SSR primers. As a result it got a linkage genetic map which contained nine linkage groups, 103 markers. The linkage genetic map covered 861.6cM with an average interval of 8.4cM. Number of markers in linkage groups varied from 5 to 21, which covered the genetic length from 34.8cM to 183.6cM, average interval distance from 5.0cM to 12.6cM The SSR markers in nine linkage groups were not evenly covered, every linkage group showed a gap above 10cM, in which the largest one was 39.7cM. Also, there were some concentrated regions, especially in LG7.The 80.58% SSR markers in the linkage map showed seriously segregation distortion, in which 49 (59.04%) makers deviated to 90196 and 34 (40.96%) makers deviated to 86101. This showed that the DH lines deviated to the genotype of 90196 in the heredity.(5)MapQTL4.0 software and composite interval mapping method were employed in studying the quantitative trait loci (QTL) controlling important head quality traits in broccoli. Six QTL related the head-leaf,head-color and head-stem hole traits were mapped. The result showed that: two QTL for head-leaf trait, the LOD value were 4.67 and 4.59 respectively, which explained the variance of trait 13.6% and 17.5%, the additive effects were 0.18 and 0.21 respectively; one QTL for head-color trait, the LOD value was 6.80, the contributory ratio was 21.5%, the additive effect was -0.74; three QTL for head-stem hole trait, the LOD value were 10.88,2.99 and 3.23 respectively, which explained the variance of trait 22.6%,7.1%and 5.9%, the additive effects were -0.22,-0.12 and -0.12 respectively.
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