| The inner leaf of Chinese Cabbage(Brassica campestris L. ssp. pekinensis) are mainly divided into white, orange and yellow. Colored head leaves have a brighter appearance as well as higher nutrition, and thus this trait has attracted more attention from researchers. In order to analyse the hereditary character and the gene action of colored leaf, we carried out the present studies. HPLC strategy was adopted to determine the carotenoid contents of several Chinese cabbage inbred lines (including white, orange and yellow leaf), and to confirm the differences existing in the different cultivars. The inheritance of orange inner leaf, yellow inner leaf, orange cotyledon, and orange flower were studied through cross breeding. The gene conferring to orange inner leaf was studied by molecular marker and BSA strategy and was mapped to the corresponding chromosome. A genetic linkage map of Chinese cabbage was constructed using SSR and SRAP markers for QTL mapping of the yellow inner leaf. The main results of the present study were as follows:1. The present studies were conducted with materials of wihte, orange and yellow inner leaf cultivars. Four carotenoids, including xanthin, lycopene,α-carotenoids andβ-carotenoids, were examined by carrying out HPLC analysis. The results showed that lycopene was not detected in white inner leaf cultivar and the contents gradient of the other 3 carotenoids were (3-carotenoids> xanthin> a-carotenoids. In orange inner leaf cultivar, the contents gradient were lycopene>β-carotenoids> xanthin> a-carotenoids. In yellow inner leaf cultivar. lycopene was also not detected and the contents gradient were xanthin>β-carotenoids> a-carotenoids. Comparing the studies of white inner leaf cultivars, orange inner leaf cultivars and yellow inner leaf cultivars, we found that in terms of xanthin content, yellow leaf cultivars showed the highest level; in terms of a-carotenoids content, orange leaf cultivars showed slightly high level; in terms ofβ-carotenoids content, yellow leaf cultivars showed slightly high level; in terms of lycopene content, it was only detected in orange leaf cultivars;2. Crossing combinations were developed to analysis the inheritance of orange leaf and yellow leaf traits of Chinese cabbage. It was confirmed that the orange inner leaf is controlled by a single recessive gene and the yellow inner leaf is controlled by multiple genes. The orange cotyledon and orange flower were also controlled by single recessive gene by observing the cotyledon color in germination stage and the flower color after the plant undergoing vernalization treatment in greenhouse. We found that orange cotyledon and flower were co-segregated with the orange leaf trait, which was inferred as the distinguishing express results of a same gene in different organs. In the practical breeding program, orange cotyledon and flower can be used as morphological markers for early selection of the expected plant.3. Marker analysis was carried out with BSA strategy and 5 SSR markers linking to or gene were developed with an F2 population derived from crossing 07A163×Chiifu. Three markers, sau(C)586. syaul9 and syaul5. were mapped to both sides of or with genetic distances of 1.6 cM.1.3 cM and 3.3 cM respectively. The or gene was mapped between BAC clones KBrH010M08 and KBrB017P15 on A09, covering a genetic distance of 4.6 cM or a physical distance of 671.271 kb. A partial linkage map of or region was constructed by the 5 SSR markers and 2 morphological markers (orange cotyledon and orange flower).4. We aligned the present linkage map to some reported studies and found the gene mapped to A09 in this study is likely to be the same one of the previous reports through the distances to or gene of anchor SSR marker ENA21 and Ni4D09. When making "blast" analysis with an orange mutant gene sequence (named Or) in cauliflower, one BAC clone in B.rapa (KBrB073I16) with relatively high homology was detected. Since we are not able to obtain the chromosome information of KBrB073I16, it is recommended to determine the correlation toward the orange mutant gene between Chinese cabbage and cauliflower in the future.5. A genetic linkage map of Chinese cabbage was developed with 71 SSR markers and 145 SRAP markers of an F2:3 population derived from a crossing 07A237×Chiifu, covering a total genetic distance of 819.4 cM and an average map distance of 3.8 cM. Twenty-five markers (14 SSR and 11 SRAP) distorted from the expected Mendel segregation ratio and accounted for a segregation distortion ratio of 11.2%. The molecular markers assign to 10 linkage groups and there is at least one anchor SSR marker on each group, which enables the genetic linkage map to be aligned to the reported maps of Chinese cabbage.6. Visual testing and portable colorimeter testing were employed to score the color in the inner leaf of Chinese cabbage. Three QTLs. accounting for 40% of the total phenotypic variance, were detected by conducting CIM strategy. The data of phenotype value obtained by different methods showed significant correlation (P< 0.01), but the identification of QTLs were diverse. This suggests that different phenotype measurements may lead to different results in QTL analysis. The QTL on A09, which matches with the end of chromosome 1, is located in the same position of the gene (or) conferring to orange inner leaf in Chinese cabbage, which corresponded with the previous studies. By anchoring SSR markers to the corresponding chromosome, the QTLs were mapped to Chr07. Chr01 and Chr10 of Chinese cabbage. |
