Association Analysis For Main Agronomic Traits And Identification Of LMW-GS Composition In Durum Wheat(Triticum Turgidum L.durum(Desf.))

Durum wheat(Triticum durum,AABB,2n=4x=28),a tetraploid cultivated wheat,is the second wheat crop after the common wheat accounting for about 10% of the total wheat area in the world,which is one of the important food crops.Durum wheat,domesticated from wild emmer(Triticum dicoccoides L.,AABB,2n=4x=28),possesses abundant variation on many traits and good environment adaption ability during the process of evolution and domestication in long-term complex environmental conditions,and is the secondary gene source of common wheat.Thus,the genetic evaluation and main agronomic traits analysis of durum wheat are significant for exploitation of excellent germplasm resources and utilization in durum wheat and common wheat breeding.In this study,firstly,the phenotypes of 10 main agronomic traits of 150 world-wide origined durum wheat were identified in four consecutive years with three replications;then,1366 single nucleotide polymorphisms(SNP)markers based on EST were used to analyze the genetic diversity,population structure and linkage disequilibrium(LD)of the 150 durum wheat;and then,association mapping analysis between 1366 SNP markers and the 10 quantitative traits was performed based on the mixed linear model(MLM);moreover,the composition of low molecular weight glutenin(LMW-GS)for 150 durum wheat accessions were identified by MALDI-TOF-MS.The main results were summarized as follows:1.The phenotypes variation of 10 main agronomic traits in durum wheat: there exists rich variation between 10 main agronomic traits in durum wheat,all of the observed traits showed continuous distribution,and are typical quantitative traits.Most of the observed traits showed significant correlation with others,Estimation of broad-sense heritability(H2)showed that all of the traits have high heritability(H2>80%).Therefore,this phenotype data of agronomic traits can be used in further analysis.Moreover,some accessions with with excellent agronomic traits can be further validated for use.2.Genetic diversity analysis in durum wheat: 1366 SNPs were used to analyze the genetic diversity of durum wheat,the results indicated that durum wheat have higher genetic diversity,the mean Nei's genetic diversity and PIC values were 0.2395 and 0.1950,respectively.Generally,the genetic diversity of B genome was higher then A genome.The genetic diversity of cultivars and landraces in different ecological regions and different release periods also showed great differences.3.Population structure analysis of durum wheat: Population structure analysis showed that observed durum wheat germplasms can be divided into two genetically distinct groups.Different groups of durum wheat did not show the obvious similarity based on national and regional,however,several materials from some ecological geographical region showed certain correlation,and the cluster of the materials released in different period showed a certain consistency.4.Linkage disequilibrium(LD)analysis of durum wheat: Durum wheat was detected with high LD level.The extent of LD was varying on both the chromosome and genome levels,the extent of LD of A genome was larger than the B genome in general.The percentage of all possible locus pairs showing highly significant LD(R~2>0.1;p<0.001)ranged from 2.4%(1A)to 7.4%(2A),the average R~2 values varied from 0.043(1B)to 0.113(4A)among the 14 chromosomes.Based on the latest physical location of EST markers,the extend of LD decay was evaluated at chromosome and genome level,and the average distances of LD decay vary in different chromosomes.Generally,the average distance of A genome was greater than B genome.5.Association mapping of 10 main agronomic traits in durum wheat: Association mapping of the 10 quantitative traits was performed based on the mixed linear model(MLM)in four consecutive years,In total,165 significant associations were detected,the number of markers associated with each trait ranged from 1 to 54,and the percentage of the total variation explained by marker ranged from 5.0% to 26.1%?Several markers were associated with one trait,and also some markers were associated with multiple traits.Some of the associated markers were in agreement with previous quantitative trait loci(QTL)analyses.Seven associations(4 for LMS,3 for PH)were detected in all the four years,two associations(1 for PH,and 1 for SMS)were detected in three of the four years,and eleven associations were detected in two of the four years.These reproducible associations were significant and more reliable.The function and homology analyses of the corresponding ESTs of some SNP markers could explain many of the major genes controlling agronomic traits.Meanwhile,some QTLs clusters for SNP associations with the observed traits were detected generally in specific chromosome regions of the wheat genome,mainly in 2A,5A,6A,7A,1B,and 6B chromosomes.6.Identification of LMW-GS alleles in durum wheat: Totally,twelve LMW-GS alleles were detected at loci Glu-A3 and Glu-B3,including 2 novel alleles represented by abnormal subunits.Five reported alleles were identified at the Glu-A3 and Glu-B3 loci,respectively.At the Glu-A3 locus,Glu-A3 e,Glu-A3a/c,Glu-A3 d,Glu-A3 f and Glu-A3 b accounted for 43.0%,16.1%,10.1%,12.8% and 7.4% of the accessions,respectively,and at the Glu-B3 locus,Glu-B3 d,Glu-B3 b and Glu-B3 c accounted for 60.4%,6.0% and 6.0% respectively,Glu-B3 h was deteted in 4 accessions,and Glu-B3 f only in one accession.Moreover,two new alleles were identified at Glu-A3 and Glu-B3 loci,encoding novel subunits with molecular weights around 40500 Da and 41260 Da,respectively.