Rapeseed (Brassica napus L.) is one of the most important oil crops almost all over the world. Seed-related traits, including oil content (OC), silique length (SL), seeds per silique (SS), and seed weight (SW), are primary targets for oil yield improvement. To dissect the genetic basis of these traits, 192 recombinant inbred lines (RILs) were derived from two parents with distinct oil content and silique length. High-density linkage map with a total length of 1610.4 cM were constructed using 1,329 double-digestion restriction site associated DNA (ddRAD) markers, 107 insertion/deletions (INDELs), and 90 well-distributed simple sequence repeats (SSRs) markers. A total of 37 consensus quantitative trait loci (QTLs) were detected for the four traits, with individual QTL explained 3.1-12.8% of the phenotypic variations. Interestingly, one OC consensus QTL (cqOCA10b) on chromosome A10 was consistently detected in all three environments, and explained 9.8% to 12.8% of the OC variation. The locus was further delimited into an approximately 614 kb genomic region, in which the flanking markers could be further evaluated for marker-assisted selection in rapeseed OC improvement and the candidate genes targeted for map-based cloning and genetic manipulation.

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A set of intervarietal substitution lines were developed in rapeseed by recurrent backcrossing and marker-assisted selection and employed for mapping both qualitative and quantitative traits. Intervarietal substitution lines (ISLs) may be assembled into advanced secondary mapping populations that have remarkable potential for resolving trait loci and mapping candidate genes. To facilitate the identification of important genes in oilseed rape (canola, Brassica napus), we developed 89 ISLs using an elite cultivar 'Zhongyou 821' (ZY821) as the recipient and a re-synthesized line 'No.2127' as the donor. In the whole process of ISLs development, the target chromosome segments were selected based on the genotypes of 300 microsatellite markers evenly distributed across the genome. Eighty-nine ISLs fixed at BCF were genotyped by sequencing using double digestion to survey the lengths of target substitution segments from the donor parent and the background segments from the recurrent parent. The total length of the substituted chromosome segments was 3030.27 Mb, representing 3.56 × of the Darmor-bzh reference genome sequence (version 4.1). Gene mapping was conducted for two qualitative traits, flower colour and seed-coat colour, and nine quantitative traits including yield- and quality-related traits, with 19 QTLs identified for the latter. Overlapping substitution segments were identified for flower colour and seed-coat colour loci, as well as for QTLs consistently detected in 2 or 3 years. These results demonstrate the value of these ISLs for locus resolution and subsequent cloning, targeted mutation or editing of genes controlling important traits in oilseed rape.

Chemical-induced male sterility (CIMS) is a method for hybrid rapeseed (Brassica napus L.) production. Some sulphonylurea herbicides such as tribenuron-methyl (TBM) are used as chemical hybridization agents (CHAs) in CIMS systems. However, the male parents must be protected from herbicide injury with a shield during spraying of the female parents with CHAs to induce male sterility. Thus, using herbicide-resistant rapeseed lines as the male parents can significantly simplify the seed production procedure and reduce the cost in hybrid seed production. A rice cytochrome P450 hydroxylase, OsCYP81A6, has been previously characterized to confer resistance to bentazon and sulphonylurea herbicides. We demonstrate here that the introduction of OsCYP81A6 renders rapeseed plants resistant to TBM. Compared with wild-type plants, the transgenic plants displayed normal stamen development and male fertility when treated with 0.05 mg/l of TBM, the dose used for inducing male sterility in hybrid seed production. These results indicate that the OsCYP81A6-expressing rapeseed plants can be used as the male parents for hybrid rapeseed production using CIMS.