Identification And Validation Of Quantitative Trait Loci For Fusarium Crown Rot Resistance In The Synthetic Hexaploid Wheat SHW-L1

Fusarium crown rot（FCR）is a soil-borne disease caused by the fungus of the genus Fusarium,which has caused enormous economic losses in major cereal-growing regions worldwide.In recent years,as a new disease in China,the incidence and severity of FCR progressively increased,which has a positive effect on wheat yield.To date,the genetic research of FCR resistance is still rare worldwide.Although some quantitative trait loci（QTL）conferring FCR resistance has been identified in partial resistant genotypes,the FCR resistant gene or molecular mechanisms for FCR resistance is still poorly understood,which seriously restricts the genetic research and wheat breeding for FCR resistance.Synthetic hexaploid wheat（SHW）with abundant genetic variation of tetraploid wheat and Aegilops tauschii have been artificially developed to address this issue.To identify and characterize QTL conferring FCR resistance,we evaluated a number of SHW lines and found that SHW-L1 showed good FCR resistance,which evaluated as medium susceptible for FCR resistance.Thus,we assessed a recombinant inbred line population of SHW-L1×CM32（SW）for FCR resistance in seedling and adult plant field trials.Combined with disease index（DI）,QTL for FCR resistance were mapped using high-density genetic maps existing 144081 molecular markers.Furthermore,a kompetitive allele-specific polymerase（KASP）marker was developed for major QTL and used to validate its genetic effect in an F₂segregation population.Homologous annotations,in silico gene expression,and q RT-PCR analysis revealed that putative candidate genes in the region of major QTL.The main findings were listed as follows:1.Identify the resistance of SW population in seedling and adult plant field trials,and correlation analysis showed that the FCR resistance had no significant correlation between plant height or heading date.We evaluated the FCR resistance of 138 lines of SW population,and phenotypic analysis showed that the DI frequency distribution graph tended to a normal distribution using disease index of three repititions of seeding trials and two repititions of adult plant trials.In the seedling and adult plant field trials,the parent SHW-L1 displayed higher resistance to FCR than CM32.The heritability analysis showed that the broad-sense heritability between SDL and AP was 0.74,which belonged to the medium and high heritability.Pearson correlation analysis showed that the FCR resistance had no significant correlation between plant height or heading date neither in the seedling nor adult plant trials based on best linear unbiased prediction（BLUP）value.2.A total of six QTL for FCR resistance were detected,and KASP marker was developed and used to validate the major QTL,which enriched the genetic research of FCR resistance in SHW.Six putative QTL conferring seedling and adult plant FCR resistance were identified on chromosomes 3B（2）,6A,6B（2）and 6D,and these QTL could explain up to8.50-16.50%of the phenotypic variance.Resistance alleles of these six were all inherited from the synthetic hexaploid wheat SHW-L1.Except Qfcr.sicau.3B.1,the other five QTL were novel.Among these six,two stable QTL Qfcr.sicau.6B.1 and Qfcr.sicau.6D could be consistently detected in all seedling and adult plant field trials,whereas the other four appeared to be seedling-specific.All these putative QTL were not significantly affected by heading date or plant height with the exception of Qfcr.sicau.6A.KASP markers were developed for major QTL Qfcr.sicau.6B.1 and Qfcr.sicau.6D,respectively.Unfortunately,only the marker KASP-3147 can successfully track the locus Qfcr.sicau.6B.1.KASP-3147was used to genotype in the F₂segregation population of SM114×XKM475,and the results showed that lines carrying resistant allele of Qfcr.sicau.6B.1 can decrease 21.03%the FCR severity.3.Candidate genes were predicted in the intervals of Qfcr.sicau.6B.1 and Qfcr.sicau.6D,and q RT-PCR analysis were conducted,which provided reference for further research of candidate genes and the mechanism of FCR resistance.Homologous annotations were performed for genes using Arabidopsis and Rice as backgrounds.Combined homologous annotations and in silico gene expression,eight genes associated with disease resistance were considered potential candidate genes for Qfcr.sicau.6B.1 and Qfcr.sicau.6D.q RT-PCR analysis revealed that three putative candidate genes,Traes CS6B02G039900 and Traes CS6D02G033700 encoding receptor-like protein kinases and Traes CS6B02G050300LC encoding NBS-LRR protein may involve in regulating FCR resistance in wheat.Our results provide valuable information for further cloning FCR resistance gene.