Genetic Analysis Of Traits Associated With Plant Architecture In A Brassica Napus Alien Introgression

Rapeseed(Brassica napus L.,2n = 38,AACC)is a globally important crop,which provides vegetable oil for humans,fodder for animals and biodiesel production for industry.Ideal plant architecture(PA)is now a major goal in rapeseed breeding,because it enables more efficient light capture,and is suitable for high-density planting and mechanical harvesting.QTL mapping and genetic analysis for PA-related traits provides a basis for rapeseed molecular breeding.In this study,we developed one doubled haploid(DH)population from a cross involving one Capsella bursa-pastoris derived B.napus intertribal introgression line with compressed branches,and constructed a high-density SNP linkage map.QTL mapping revealed some QTL/ candidate genes associated with branch angle,and some co-localized QTL for plant height(PH),branch initiation height(BIH),stem diameter(SD)and flowering time(FT).1.DH population and high-density linkage map construction In this study,we developed one DH population encompassing 208 lines from a cross between B.napus introgression line Y689(with compressed branches)and B.napus cultivar Westar.Using 60 K SNP array,a high-density SNP map with 3,073 available SNP markers was constructed,covering a length of 2,242.14 cM and an average marker interval of 0.73 cM.All available SNPs were used to perform a BLASTN search through the B.napus reference genome,and a translocation was shown between chromosomes A02 and C02;large deletions were shown on chromosomes A06,A08,C01,and C07,respectively,indicating that the introgression of Y689 might suffer a big genomic variation during the process of wide hybridization.2.QTL mapping for branch angle In 2014-2016,we planted the YW-DH population in semi-winter-type,winter-type,and spring-type rapeseed growing areas,and measured the branch angle.Together with the genotyping data,17 additive QTL were identified by whole-genome QTL scanning.One QTL(qBA.A03-2)on chromosome A03 could be repeatedly detected,and explained 10.21%-13.21% of the phenotypic variation;two adjacent QTL on chromosome C03 could also be repeatedly detected,and explained 10.55%-21.73% and 14.02%-17.21% of the phenotypic variation,respectively.Comparing with the previous study,these three major QTL were newly founded.Two candidate genes,BnaC03g14890 D and BnaC03g16420 D,orthologs to Arabidopsis thaliana SAUR30 and SAUR55,which belongs to early auxin response gene family might affect the branch angle of B.napus.3.Co-localized major QTL associated with PH,BIH SD,and FT Phenotypic analysis of the YW-DH population across multiple environments revealed that PH,BIH,SD,and FT were significantly correlated with one another.PH was significantly and positively correlated with BIH,SD,and FT(r = 0.67,0.76 and 0.61,respectively);BIH was also significantly and positively correlated with SD and FT(r = 0.53 and 0.68);SD was significantly and positively correlated with FT(r = 0.54).QTL mapping revealed 5 major QTL for PH,with mean PVE 10.81%-22.97%;5 major QTL for BIH,with mean PVE 9.69%-21.99%;5 major QTL for SD,with mean PVE 11.19%-16.58%;and 4 major QTL for FT,with mean PVE 11.76%-30.89%.Of the 19 major QTL,11 of them were newly detected,including 3,3,and 5 QTL for PH,BIH,and SD,respectively.Theses nineteen major QTL associated with PH,BIH,SD and FT were all distributed on chromosomes A02 and A07,which organized two QTL clusters on A02: 1.4-24.6 cM and A07: 104.0-122.2 cM.The QTL within two QTL clusters were integrated into 3 and 4 unique QTL,respectively.To analyze the genetic basis(tight linkage or pleiotropy)of the QTL clusters,conditional QTL mapping was performed.As a result,genes regulating the four traits within the cluster on A02 might show pleiotropy,and the genes on A07 cluster might show tight linkage.These results provided valuable information for QTL fine mapping and molecular breeding.