Abstract
A major QTL controlling ovule abortion and SN was fine-mapped to a 80.1-kb region on A8 in rapeseed, and BnaA08g07940D and BnaA08g07950D are the most likely candidate genes. The seed number per silique (SN), an important yield determining trait of rapeseed, is the final consequence of a complex developmental process including ovule initiation and the subsequent ovule/seed development. To explore the genetic mechanism regulating the natural variation of SN and its related components, quantitative trait locus (QTL) mapping was conducted using a doubled haploid (DH) population derived from the cross between C4-146 and C4-58B, which showed significant differences in SN and aborted ovule number (AON), but no obvious differences in ovule number (ON). QTL analysis identified 19 consensus QTLs for six SN-related traits across three environments. A novel QTL on chromosome A8, un.A8, which associates with multiple traits, except for ON, was stably detected across the three environments. This QTL explained more than 50% of the SN, AON and percentage of aborted ovules (PAO) variations as well as a moderate contribution on silique length (SL) and thousand seed weight (TSW). The C4-146 allele at the locus increases SN and SL but decreases AON, PAO and TSW. Further fine mapping narrowed down this locus into an 80.1-kb interval flanked by markers BM1668 and BM1672, and six predicted genes were annotated in the delimited region. Expression analyses and DNA sequencing showed that two homologs of Arabidopsis photosystem I subunit F (BnaA08g07940D) and zinc transporter 10 precursor (BnaA08g07950D) were the most promising candidate genes underlying this locus. These results provide a solid basis for cloning un.A8 to reduce the ovule abortion and increase SN in the yield improvement of rapeseed.
Highlights
Rapeseed (Brassica napus L., 2n = 38, AACC) is one of the most important oil crops worldwide that provide more than 15% of the global supply of edible vegetable oil (USDA ERS 2019) and used as an important raw material for biofuel and feeding livestock
We identified a 1,445-bp deletion starting from 1,015-bp upstream of the transcription start site to the mid region of the second exon of BnaA08g07930D in C4-58B compared with the C4-146, which resulted in the formation of a pseudogene gene in C4-58B (Fig. 5a; Fig. S2)
SN is the final consequence of a complex developmental process including ovule initiation and subsequent ovule/seed development
Summary
Developing high-yielding varieties has always been one of the most important goals of rapeseed breeding because of the growing demands for vegetable oil as well as the declining hectarage used for rapeseed production (Sun et al 2018). A highly significant positive correlation was observed between SN and seed yield, indicating that increasing SN should be effective for improving rapeseed production. There is a rich variation for SN in rapeseed, the SN of the current cultivars (~20) is far below its maximum (> 30) in the germplasm resources (Chen et al 2014), indicating that the potential of SN is yet to be maximized effectively in rapeseed yield improvement. Understanding the genetic basis of SN is of great importance for yield improvement through the utilization of advantageous variations in rapeseed breeding and for plant evolution and crop domestication
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