Rapeseed research and production in China

Rapeseed(Brassica napus L.) is the largest oilseed crop in China and accounts for about 20% of world production.For the last 10 years,the production,planting area,and yield of rapeseed have been stable,with improvement of seed quality and especially seed oil content.China is among the leading countries in rapeseed genomic research internationally,having jointly with other countries accomplished the whole genome sequencing of rapeseed and its two parental species,Brassica oleracea and Brassica rapa.Progress on functional genomics including the identification of QTL governing important agronomic traits such as yield,seed oil content,fertility regulation,disease and insect resistance,abiotic stress,nutrition use efficiency,and pod shattering resistance has been achieved.As a consequence,molecular markers have been developed and used in breeding programs.During 2005–2014,215 rapeseed varieties were registered nationally,including 210 winter-and 5 spring-type varieties.Mechanization across the whole process of rapeseed production was investigated and operating instructions for all relevant techniques were published.Modern techniques for rapeseed field management such as high-density planting,controlled-release fertilizer,and biocontrol of disease and pests combined with precision tools such as drones have been developed and are being adopted in China.With the application of advanced breeding and production technologies,in the near future,the oil yield and quality of rapeseed varieties will be greatly increased,and more varieties with desirable traits,especially early maturation,high yield,high resistance to biotic and abiotic stress,and suitability for mechanized harvesting will be developed.Application of modern technologies on the mechanized management of rapeseed will greatly increase grower profit.

Key genes and mechanisms underlying natural variation of silique length in oilseed rape(Brassica napus L.)germplasm

Silique length influences seed yield in oilseed rape.It shows extensive variation in germplasm resources,and identifying the underlying genes and regulatory mechanisms would advance breeding for the trait.In the present study,a genome-wide association study(GWAS)using 331 core accessions planted in 10 environments revealed 13 loci associated with silique length on chromosomes A01,A04,A07,A09,and C03,explaining 6.2%–19.2%of phenotypic variance.Physiological analysis showed that silique length variation was attributable to differences in silique growth rate and/or duration before four weeks after flowering,with levels of endogenous phytohormones(auxin,ethylene,and GA24,GA12,and GA44)playing an important role.Cytological analysis showed that silique length variation was due mainly to differences in cell number followed by cell size.Transcriptomic analysis of two pools of silique walls with opposite length extremes revealed 3248 differentially expressed genes(DEGs).These DEGs were enriched in several pathways(such as cell wall,cell division,and hormone metabolism)associated with cell proliferation and expansion and silique development.Integrating GWAS,RNA-seq,and functional annotation results revealed 15 candidate genes for the major associated locus q SL.A09-3.Of these,Bna A9.ARF18 and Bna A9.CYP78 A9 were validated by haplotype analysis followed by candidate gene association.Sequence variation in the coding region of Bna A9.ARF18 and expression of Bna A9.CYP78 A9 in silique walls were strongly associated with silique length.Our results provide an explanation for the natural variation of silique length in oilseed rape germplasm and offer useful information for its improvement.

Genetic dissection of root morphological traits as related to potassium use efficiency in rapeseed under two contrasting potassium levels by hydroponics

To reveal the genetic basis of potassium use efficiency(KUE) in rapeseed, root morphology(RM), biomass and KUE-related traits were measured in a recombinant inbred line population with 175 F7 lines that were subjected to high-potassium(HK) and low-potassium(LK) treatments by hydroponics. A total of 109 significant QTLs were identified to be associated with the examined traits. Sixty-one of these QTLs were integrated into nine stable QTLs. The higher heritability for RM and biomass traits and lower heritability for KUE-related traits, as well as nine stable QTLs for RM traits and only two for KUE-related traits,suggested that regulating RM traits would be more effective than selecting KUE traits directly to improve KUE by markerassisted selection. Furthermore, the integration of stable QTLs identified in the HK, LK, high-nitrogen(HN) and low-nitrogen(LN) conditions gave 10 QTL clusters. Seven of these clusters were classified into major QTLs that explained 7.4%–23.7% of the total phenotypic variation. Five of the major QTL clusters were detected under all of the treated conditions, and four clusters were specifically detected under the LK and LN conditions. These common and specific QTL clusters may be useful for the simultaneous improvement of multiple traits by marker-assisted selection.