Genome-wide association mapping for grain shape and color traits in Ethiopian durum wheat(Triticum turgidum ssp.durum)

Grain shape and color strongly influence yield and quality of durumwheat.Identifying QTL for these traits is essential for transferring favorable alleles based on selection strategies and breeding objectives.In the present study,192 Ethiopian durum wheat accessions comprising 167 landraces and 25 cultivars were genotyped with a high-density Illumina iSelect 90K singlenucleotide polymorphism(SNP)wheat array to conduct a genome-wide association analysis for grain width(GW),grain length(GL),CIE(Commission Internationale l'Eclairage)L*(brightness),CIE a*(redness),and CIE b*(yellowness)traits.The accessions were planted at Sinana Agricultural Research Center,Ethiopia in the 2015/2016 cropping season in a complete randomized block design with three replications.Twenty homogeneous and healthy seeds per replicate were used for trait measurement.Digital image analysis of seeds with GrainScan software package was used to generate the phenotypic data.Analysis of variance revealed highly significant differences between accessions for all traits.Atotal of 46 quantitative trait loci(QTL)were identified for all traits across all chromosomes.One novelmajor candidate QTL(−lg P≥4)with pleiotropic effects for grain CIE L*(brightness)and CIE a*(redness)was identified on the long armof chromosome 2A.Eighteen nominal QTL(−lg P≥3)and 26 suggestive QTL(−lg P≥2.5)were identified.Pleiotropic QTL influencing both grain shape and color were identified.

Resequencing of 145 Landmark Cultivars Reveals Asymmetric Sub-genome Selection and Strong Founder Genotype Effects on Wheat Breeding in China

Controlled pedigrees and the multi-decade timescale of national crop plant breeding programs offer a unique experimental context for examining how selection affects plant genomes.More than 3000 wheat cultivars have been registered,released,and documented since 1949 in China.In this study,a set of 145 elite cultivars selected from historical points of wheat breeding in China were re-sequenced.A total of 43.75 Tb of sequence data were generated with an average read depth of 17.94x for each cultivar,and more than 60.92 million SNPs and 2.54 million InDels were captured,based on the Chinese Spring RefSeq genome v1.0.Seventy years of breeder-driven selection led to dramatic changes in grain yield and related phenotypes,with distinct genomic regions and phenotypes tar-geted by different breeders across the decades.There are very clear instances illustrating how introduced Italian and otherforeign germplasm was integrated into Chinese wheat programs and reshaped the genomic landscape of local modern cultivars.Importantly,the resequencing data also highlighted significant asymmetric breeding selec-tion among the three sub-genomes:this was evident in both the collinear blocks for homeologous chromosomes and among sets of three homeologous genes.Accumulation of more newly assembled genes in newer cultivars implied the potential value of these genes in breeding.Conserved and extended sharing of linkage disequilibrium(LD)blocks was highlighted among pedigree-related cultivars,in which fewer haplotype differences were detected.Fixation or replacement of haplotypes from founder genotypes after generations of breeding was related to their breeding value.Based on the haplotype frequency changes in LD blocks of pedigree-related cultivars,we propose a strategy for evaluating the breeding value of any given line on the basis of the accumulation(pyramiding)of bene-ficial haplotypes.Collectively,our study demonstrates the influence of "founder genotypes" on the output of breeding efforts over many decades and also suggests that founder genotype perspectives are in fact more dy-namic when applied in the context of modern genomics-informed breeding.