Identification of QTLs for seed quality traits in rapeseed (Brassica napus L.) using recombinant inbred lines (RILs)

Rapeseed (Brassica napus L.) is the most important edible oilseed crop in China and the second most important globally after soybean. It provides edible vegetable oil for human consumption and proteins for the feed industry, and has recently gained increasing interest as a source of biodiesel. The improvement of seed quality traits for high protein, oil and oleic acid, and low erucic acid and glucosinolate content remains the most important breeding goal in B. napus. Mapping of quantitative trait loci (QTLs) underlying seed quality traits will allow us to enrich knowledge on these traits and improve the efficiency and precision of conventional rapeseed breeding via marker-assisted selection (MAS). In this study, a genetic linkage map comprising 181 markers (143 sequence-related amplified polymorphisms (SRAPs) and 38 simple-sequence repeats (SSRs)) and 19 linkage groups covering 1307.99 cM was constructed with 94 F₇–₈ recombinant inbred lines (RILs) derived from a cross between a high oil content line ‘827R’ and a low oil content line ‘Darmor_Sin’. A total of nine QTLs were identified (LOD > 2.5) on four chromosomal regions (LG1, LG10, LG11 and LG12) for seed quality traits: four for oil content (qOC-1, 2, 3, 4), two for protein content (qPC-1, 2), two for oleic acid content (qOAC-1, 2), and one for glucosinolate content (qGLC-1). The phenotypic variance explained by individual QTL was estimated as 7.70, 14.58, 16.00, and 23.11 % respectively for the four oil content QTLs; 13.16 and 14.81 % for the two protein content QTLs; 12.52 and 25.48 % for the two oleic acid content QTLs; and 47.71 % for the glucosinolate content QTL. The overall phenotypic variation explained by the identified QTLs was 61.39 % for oil content, 27.97 % for protein content, 38.00 % for oleic acid content and 47.71 % for glucosinolate content. Of the two QTLs identified for seed protein content, one (qPC-1) was tightly linked to a QTL for oil content (qOC-1) on LG1 and another one (qPC-2) was co-localized with a second QTL for seed oil content (qOC-2) on LG11. The two pairs of QTLs affected both traits with opposite additive effects confirming the negative correlation between oil and protein content in rapeseed. The present results will be of value for ongoing efforts to dissect the molecular basis of seed quality traits and practicing MAS in B. napus breeding programs.