| The F2 mapping population was derived by crossing two diverse Chinese cabbage lines ’501 and 601’. The maternal parent’501’is a microspore culture-derived double-haploid (DH) line with a small leaf head, light leaf color. The paternal parent’601’is an inbred line with a heavy leaf head, heavy leaf color. The seeds of the F3 families harvested from each F2 line of the mapping population (501,601). In the present study, an attempt has been made to constructe a linkage map and analyzes QTL mapping of leaf head-related traits and chlorophyll-related traits. All results were described as follows:1. Of the 450 unigene derived microsatellite (UGMS) primer pairs,428 (95.1%) produced repeatable and reliable amplifications of expected size in at least one parental line of Chinese cabbage and 70 UGMS markers gave 72 polymorphic loci between the two contrasting parental lines. Linkage analysis with 70 UGMSs (72 marker loci),154 simple sequence repeats (SSRs) and one phenotypic marker gave 10 linkage groups (LGs) with a total genome coverage of 933.9 cM and the average distance between adjacent loci was 4.11 cM. Most of the markers segregated following the expected 1:2:1 Mendelian segregation ratio (P< 0.01) in the F2mapping population and only 31 (13.7%) markers deviated significantly from this ratio. A few markers showing skewed segregation ratios were clustered on A7 and A9. Cross-species transferability analysis of these 70 polymorphic UGMS markers in five other cultivated Brassica species showed varying transferability rates ranging from 82.9% in B. nigra to 97.1% in B. juncea and B. napus and overall 53 UGMS markers amplified targets in all five species.2. Alignment of the current genetic map with the Arabidopsis genome was conducted using a total of 147 markers (48 UGMS and 100 SSR marker loci). The five chromosomes of Arabidopsis thaliana were divided into many segments and distributed to various regions of the Chinese cabbage map. The total length of 84 collinear segments with A. thaliana chromosomes in Chinese cabbage was 627.7 cM (67.2%). This coverage reflected an average length of 6.7 cM per collinear region for the A genome.3. The two Chinese cabbage parental lines, accessions’601’and’501’, were contrasting for seven traits analyzed which included gross weight (GW), number of non-wrapper leaves (NNWL), head weight (HW), head length (HL), head width (HWI), head length/head width ratio (HLHWR) and number of head-forming leaves (NHFL). Transgressive segregation and continuous distribution were observed for all the traits in the F3 lines. The correlation coefficients analyses showed that most of the traits were significantly correlated with each other. Composite interval mapping using WinQTLCart (ver.2.5) detected a total of 27 QTL in ten LGs for the seven traits analyzed. Of the 27 QTL detected in ten LGs, several QTL were found to map in the same QTL region of a few LGs. The QTL region of A2, A4, A6 and A8 showed multiple QTL for three or more traits. Analyses of gene functions of individual QTL revealed the influence of both additive and dominance gene actions. The minority (7 out of 27 QTL) of the QTL for the seven traits analyzed were additive in nature.4. The two Chinese cabbage parental lines, accessions’601’and’501’, were contrasting for chlorophyll a and b contents traits analyzed. Transgressive segregation and continuous distribution were observed for all the traits in the F3 lines, suggesting polygenic inheritance of the traits. The correlations showed that chlorophyll a and b contents traits were significantly correlated with each other at the same year. In the contrary, these traits were not correlated with each other at different years. Totally,10 QTL were identified for the two traits in the two trials and they were detected in 7 main LGs (A1-A10). Five QTL were detected for chlorophyll a content and they were distributed in 3 linkage groups. The QTL(qClaA9a and qClaA9b) were observed at the same region of A9 between two years. Five QTL were associated with chlorophyll b content and they were distributed in 5 linkage groups. |
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