Abstract:

Although seed yield is one of the most important objectives in Brassica napus breeding program, it is poorly understood because of the multigenic and nongenetic influence. Recent advances in molecular marker techniques provide the possibilities to trace gene behavior at individual gene loci, which greatly helps to understand the complex genetics of quantitative traits of seed yield. The objective of our investigation was to acquire the information on the association between molecular markers and seed yield in Brassica napus and on the inheritance of these agronomic traits and to facilitate the selection in breeding programs. A double hapolid (DH) population derived from a cross between the rapeseed cultivars Zhongyou 821 and Bao 604 was used to identify quantitative trait loci (QTLs) for seed yield and yield components. Eighty-two double hapolid lines as well as two parent lines were evaluated in field environments in Wuhan, with two replications, for 7 agronomic traits, including plant height (PH), branch position (BP), length of main raceme (LMR), No. of primary branches (NPB), No. of pod per plant (NPP), 1000-seed weight (SW) and yield per plant (YPP). It was shown that all the seven agronomic traits had continuous phenotypic distributions and were suitable for QTL analysis (Table 2). A total of 261 molecular markers consisting of 2 RFLPs, 72 RAPDs, 91 SSRs and 86 SRAPs were employed to 82 DH lines and to construct the genetic linkage map, two hundred and fifty-one markers were assembled into 20 linkage groups (LG1–LG20), no linkage was found between the remaining 10 markers and any of the established linkage groups (Fig.1). The total map length was 1 746.5 cM with an average distance of 6.96 cM between adjacent markers. By employing complex interval mapping, a total of 17 putative QTLs were identified to be significant for the seven traits, of which 3 were for yield, 14 for yield components (Table 4). The phenotypic variation was explained by individual QTL ranged from 9.42%–17.58% for three QTLs of plant height, 8.13%–15.20% for four QTLs of branch position, 7.49%–23.36% for three QTLs of length of main raceme, 15.29%–19.58% for two QTLs of No. of primary branches, 17.42% for one QTL of No. of pod per plant, 7.64% for one QTL of 1000-seed weight and 8.11–9.78 for three QTLs of yield per plant. Some QTLs were mapped at the same or similar position in LG4, there were significant correlations between the corresponding traits. It suggested that the pleiotropism or tight linkage of QTLs for different traits might be the important genetic base for trait correlations. The molecular marker linked closely with main QTLs of yield and yield components in this paper could be used for MAS in rapeseed breeding program.

Key words: Brassica napus, DH (doubled haploid), Molecular linkage map, Yield, QTL (quantitative trait loci)