Construction Of Nearly Isogenic Lines And Development Of SSR Markers For Wheat Resistance To Orange Wheat Blossom Midge(OWBM,Sitodiplosis Mosellana Gehin)

Orange wheat blossom midge(OWBM,Sitodiplosis mosellana Gehin)is an important pest insect that seriously threatens wheat production in major wheat-production countries including China.Biologically special characteristics of orange wheat blossom midge increase the difficulty of its control.Traditional identification of insect resistance requires an insect nursery,of which construction is time-consuming and laborious.Development of markers that closely linked to or co-segregated with OWBM resistance is of great importance for indirect selection of OWBM resistance and fine-mapping of the major quantitative trait locus(QTL)tolerant to OWBM and marker-assisted breeding for resistant wheat varieties for OWBM resistance in wheat.In the previous study,the main QTL for insect resistance was identified on chromosome 4A of wheat by using two RIL lines.Meanwhile,QTL interval of 699Mb-714Mb on chromosome 4A was detected by mixed pool transcriptome sequencing,and several candidate genes were screened through gene sequence polymorphism sites.However,both primary mapping and transcriptome analysis require fine mapping to obtain and validate candidate genes.In this study,OWBM resistance of a panel of wheat accessions in China was identified.Then,the residual heterozygous line of RIL lines was used to screen for nearly isogenic line,which was subsequently used as parents to construct the secondary F2 population.Based on the mapping of the major QTL Qsm.hbau-4A,SSR markers were developed from the regions where the QTL was located,and the effectiveness of SSR markers were then analyzed in RILS and germplasm resources.This lays a foundation for fine mapping of the main QTL for insect resistance.The main research results are as follows:1.In this study,a near-isogenic line pair against OWBM about Qsm.hbau-4A was constructed,(48-3 and 48-8).The nearly isogenic line 48-8 stably show high resistance(0.00～0.09),and 48-3could stably show high sensitivity(1.81～7.12),to OWBM.Genetic similarity between this NIL pair was 97.19%.No significant differences in plant height,panicle density,grain weight per plant,spikelet number and panicle length were observed between them.In combination with background analysis and prospect analysis.48-3 and 48-8 can be used to fine map the QTL Qsm.hbau-4A).2.A total of 1210 individual plants were obtained from the F2 generation.From the OWBM resistance of F1,phenotype for the major QTL Qsm.hbau-4A was recessive.And 22 crossing cases were recovered among F2.3.Based on previous mapping of the major QTL Qsm.hbau-4A,we attempted to develop SSR markers tightly linked with this QTL,followed by marker-based genotyping in a panel of wheat accessions.Out of the 565 SSR markers developed,12%showed polymorphic between 48-3 and 48-8,whereas 2%were polymorphic in three pairs of near isogenic lines(NILs).Genotyping using these SSR markers revealed an average coincidence rate of 90.35%in RILs with variable OWBM resistance,as well as a mean value on detection efficiency of 51.04%in 566 wheat accessions showing different OWBM resistance.The marker Xhs87 represented the highest detection coincidence rate and this might be useful in screening for resistant germplasm resources.The SSR markers if relative to those produced in the former study showed mostly co-dominant and high detection efficiency.Collectively,these newly-developed markers provided a source valuable in fine mapping of Qsm.hbau-4A and marker-assisted selection of wheat OWBM resistance4.The resistance of 566 wheat germplasm resources,advanced lines and alien lines from China was identified.It was found that,on the whole,the resistance of OWBM in China was not high,and only 153 of them showed high resistance or above.5.The differential expression gene TRAESCS4A01G437400 was verified by germplasm resources,and the candidate genes were found to be effective in distinguishing resistant wheat materials in germplasm resources.