Genetic Improvement Of Important Traits Of The Elite Restorer 621R And Cultivar ’Zhongshuagn11’ In Brassica Napus L.

Clubroot and herbicide resistance,high oleic acid(OA)content and early-maturity are important breeding goals in rapeseed(Brassica napus L.).Clubroot and weeds pose serious threats to rapeseed production that can cause serious damages to rapeseed yield and quality,resulting in huge economic loss;high-OA oils are more popular for their high stability and nutritive value;and flowering time is an important agronomic trait not only for regulating the regional adaption of rapeseed that can increase its plantation area,but also for meeting the demand of the different agricultural planting systems in China.The improvement of multiple target traits simultaneously in rapeseed can be achieved by pyramiding multiple elite target genes from different germplasm resources.621R is an elite restorer line of several commercial hybrids in China,which displays high combining ability and excellent lodging resistance.However,621 R is susceptible to both clubroot and herbicides,and shows late-flowering phenotype and low-OA content.‘Zhongshuang11’(ZS11)is an elite semi-winter rapeseed cultivar,which harbor high oil content,high tolerance to sclerotinia stem rot and good adaptation to mechanized harvesting,but is sensitive to both clubroot and herbicides.In the present study,we developed six introgression lines(ILs)by pyramiding of two clubroot resistance genes(CRb and Pb Ba8.1),two herbicide-resistance genes(ALS1R and ALS3R),one high-OA allele(fad2.a5),and two early flowering alleles(flc.a2 and flc.c2)into 621 R with ‘speed breeding’ combined with marker-assisted selection and phenotypic selection.In addition,we also developed ILs by pyramiding of two clubroot-resistance genes(CRb and Pb Ba8.1)and two herbicide-resistance genes(ALS1R and ALS3R)into ZS11 by the same strategy.The main results are as follows:1.The development of markers linked to the targeted clubroot resistance genes.Two molecular markers,J64-3 and A03-50,were developed.J64-3 located between the clubroot resistant gene Pb Ba8.1 and the high erucic acid gene FAE1 could be used to break the linkage of Pb Ba8.1 and FAE1 loci,and A03-50 was linked marker of CRb.These two markers could be used for developing clubroot resistant rapeseed varieties with low erucic acid.2.The development of the ILs with the genetic background of 621 R.To improve 621 R,a backcrossing strategy in combination with marker-assisted selection was adopted,with ZHE226,HYZ62 R,R11,621 RO and 621 RH as donor parents.Six ILs were developed with four-to seven-gene combinations,i.e.,621RCH(Pb Ba8.1 +CRb + ALS1 R + ALS3R),621RCHO(Pb Ba8.1 + CRb + ALS1 R + ALS3 R + fad2.a5),621RCHF(Pb Ba8.1 + CRb + ALS1 R + ALS3 R + flc.a2),621RCHOF(Pb Ba8.1 + CRb+ ALS1 R + ALS3 R + fad2.a5 + flc.a2),621RCHFF(Pb Ba8.1 + CRb + ALS1 R + ALS3R+ flc.a2 + flc.c2)and 621RCHOFF(Pb Ba8.1 + CRb + ALS1 R + ALS3 R + fad2.a5 +flc.a2 + flc.c2),with a genome recovery rate of 95.5%,93.2%,91.8%,92.6%,90.9%,90.4%,respectively.3.Evaluation of the ILs with the genetic background of 621 R for the targeted traits and major agronomy traits.Resistance evaluation showed that all ILs were resistant to both clubroot and herbicide.The ILs 621 RCHO,621RCHOF and621 RCHOFF with average OA content of 74.1%,which was 12.4% higher than 621 R.For the flowering time(FT),the 621 RCH and 621 RCHO showed average FT of 112.7d(late-maturity),no significant difference compared with 621R;621RCHF and621 RCHOF,621RCHFF and 621 RCHOFF showed average FT of 65.2 d(middlematurity)and 50.9 d(early-maturity),which was 47.7 d and 61.9 d earlier than that of621 R,respectively.Base on the phenotype data from Gansu,Wuhan,Jiangling,a computational model that the lines used as fixed factor,the block and the environment used as random factor was employed to evaluate the performance of the ILs.The TSW of all six ILs was significantly higher than that of 621 R.The plant height(PH)of latematurity lines were significantly higher than the middle-maturity lines and the PH of middle-maturity lines were significantly higher than the early-maturity lines.The branch numbers(BN)of late-maturity lines were significantly higher than the middlematurity lines,but no significant difference was observed between middle-maturity lines and early-maturity lines.The other main agronomic traits of the six ILs were similar with the 621 R except for the NSS of 621 RCH was significantly higher than that of 621 R.4.Evaluation of the hybrids between the ILs and two male sterile lines for the targeted traits and major agronomy traits.Resistance evaluation indicated that the improved hybrids showed resistance to both clubroot and herbicide.The hybrids of616A/high-OA ILs and RG430A/high-OA ILs exhibited average OA content of 69.3%and 73.0%,which was 6.8% and 5.8% higher than the check hybrid.616A/621 RCHF and 616A/621 RCHOF with an average FT of 79.8 d,which was 28.6 d earlier than the check hybrid;616A/621 RCHFF and 616A/621 RCHOFF with an average FT of 58.2 d,which was 50.2 d earlier than the check hybrid.Similarly,RG430A/621 RCHF and RG430A/621 RCHOF with an average FT of 103.4 d,which was 9.7 d earlier than the check hybrid;RG430A/621 RCHFF and RG430A/621 RCHOFF with an average FT of65.1 d,which was 48.0 d earlier than the check hybrid.The same computational model was employed to evaluate the performance of the hybrids.The PH of late-maturity hybrids was significantly higher than the middle-maturity hybrids and the PH of middle-maturity hybrids was significantly higher than the early-maturity hybrids.The BN of late-maturity hybrids was significantly higher than the middle-maturity hybrids,but which no significant difference was observed between middle-maturity hybrids and early-maturity hybrids.There was no obvious difference between the improved hybrids and the check hybrids in other traits except that 616A/621 RCHFF showed significantly decreased YP than that of the check hybrid.5.The development and evaluation of IL with the genetic background of ZS11.Pb Ba8.1,CRb,ALS1 R and ALS3 R were introgressed from ZHE226,‘Huayouza62R’,and DK into the genetic background of ZS11,the pyramided line ZS11 CH was developed with a genetic background similarity percentage of 93.3% with ZS11.Resistance evaluation showed that ZS11 CH was resistant to both clubroot and herbicide.The same computational model was employed to evaluate the performance of ZS11 CH from Gansu and Jiangling,and no obvious difference was observed between the ZS11 CH and ZS11,indicating that the ZS11 CH may have promising potential in practical application.In summary,the above research results indicated that the genes Pb Ba8.1,CRb,ALS1 R,ALS3R,fad2.a5,flc.a2 and flc.c2 were introduced into the genetic background of 621 R,and the new developed pyramided lines conferred significantly enhanced resistance to clubroot and herbicide,high OA content,and earlier maturity.These newly developed pyramided lines can be used to breed high-yield,high-quality,clubroot-and herbicide-resistance and early-maturing rapeseed hybrids for rapeseed production.The genes of Pb Ba8.1,CRb,ALS1 R and ALS3 R were introduced into the genetic background of ZS11,and the new developed lines were not only highly resistant to clubroot and herbicide,but also had no significant difference in main agronomic traits from the ZS11,having great potential for rapeseed production.