Genomics-enabled breeding for sorghum in West Africa

Doctor of PhilosophyDepartment of AgronomyGeoffrey MorrisIn semi-arid regions, staple crop productivity is affected by multiple environmental, biological and socio-economic factors threatening food security. Sorghum (Sorghum bicolor) is adapted to semi-arid and sub-humid zones of West Africa (WA). This crop is cultivated over large areas, corresponding to variable and diversified local contexts. The genetic basis of local adaptation and farmer preferences and their applications in breeding need further studies. Recent genotyping methods have provided access to high-density markers and their applications in breeding. In this thesis, genomic resources of WA germplasm were developed using the genotyping-by-sequencing method (GBS) to understand the genetic diversity and to identify quantitative trait loci (QTLs) associated with yield components under pre-flowering water deficit. Evidence of local adaptation in genomic regions linked to flowering time in sub-humid zones and balancing selection grain pigmentation were found. Phenotyping of the WA sorghum association panel (WASAP) was conducted under experimental water-deficit treatments. Significant variations of yield components were observed suggesting local adaptation and drought tolerance in the WASAP. Genome-wide association studies identified novel QTLs controlling vegetative biomass and grain weight under water deficit treatment. QTLs colocalizing with known genes in various traits were also identified. Furthermore, these genomic resources were used to develop diagnostic markers for resistance to Striga hermonthica, a weed parasite of grass crops, in which resistance is known to be associated with a deletion of a few genes. Using GBS data, single nucleotide polymorphisms in linkage disequilibrium with the deletion to generate breeder-friendly markers were selected. Analyses identified eight SNPs, converted to breeder-friendly markers and tested in biparental populations and diverse germplasm using outsourced genotyping. The findings provide genetic resources to the scientific community and could facilitate genomics-enabled breeding of sorghum in sub-Saharan Africa

Global SNP data

In vcf format, gzippe

Nigerian SNP data (unfiltered)

In vcf format, gzipped. Not filtered for minor allele frequency

Nigerian SNP data (filtered)

In vcf format, gzipped. Filter for minor allele frequency > 0.0

Data from: Genomic signatures of adaptation to a precipitation gradient in Nigerian sorghum

Evolution of plants under climatic gradients may lead to clinal adaptation. Understanding the genomic basis of clinal adaptation in crops species could facilitate breeding for climate resilience. We investigated signatures of clinal adaptation in the cereal crop sorghum (Sorghum bicolor L. [Moench]) to the precipitation gradient in West Africa using a panel (n = 607) of sorghum accessions from diverse agroclimatic zones of Nigeria. Significant correlations were observed between common-garden phenotypes of three putative climate-adaptive traits (flowering time, plant height, and panicle length) and climatic variables. The panel was characterized at >400,000 single nucleotide polymorphisms (SNPs) using genotyping-by-sequencing (GBS). Redundancy analysis indicated that a small proportion of SNP variation can be explained by climate (1%), space (1%), and climate collinear with space (3%). Discriminant analysis of principal components identified three genetic groups that are distributed differently along the precipitation gradient. Genome-wide association studies were conducted with phenotypes and three climatic variables (annual mean precipitation, precipitation in the driest quarter, and annual mean temperature). There was no overall enrichment of associations near a priori candidate genes implicated in flowering time, height, and inflorescence architecture in cereals, but several significant associations were found near a priori candidates including photoperiodic flowering regulators SbCN12 and Ma6. Together, the findings suggest that a small (3%) but significant proportion of nucleotide variation in Nigerian sorghum landraces reflects clinal adaptation along the West African precipitation gradient

SNP Data Set of Senegalese Sorghum in the USDA-NPGS GRIN

The file contains 213,916 GBS-SNPs obtained using genotyping-by-sequencing on the Senegalese sorghum accessions in the USDA-NPGS GRIN. Single-end sequence reads obtained from Illumina sequencing HiSeq 2500 were processed with the TASSEL 5 GBS v2 pipeline and sequence tags were aligned to the sorghum reference genome, BTx623 for SNP discovery. Only SNPs with 0.01, and biallelic SNPs are present in this data set

Faye-Supporting_Information_Data_S4

The file contains significantly associated SNPs with phenotypes (photoperiod sensitivity and panicle compactness) or environment variables

Data from: Genomic signatures of adaptation to Sahelian and Soudanian climates in sorghum landraces of Senegal

Uncovering the genomic basis of climate adaptation in traditional crop varieties can provide insight into plant evolution and facilitate breeding for climate resilience. In the African cereal sorghum (Sorghum bicolor L. [Moench]), the genomic basis of adaptation to the semiarid Sahelian zone versus the subhumid Soudanian zone is largely unknown. To address this issue, we characterized a large panel of 421 georeferenced sorghum landrace accessions from Senegal and adjacent locations at 213,916 single‐nucleotide polymorphisms (SNPs) using genotyping‐by‐sequencing. Seven subpopulations distributed along the north‐south precipitation gradient were identified. Redundancy analysis found that climate variables explained up to 8% of SNP variation, with climate collinear with space explaining most of this variation (6%). Genome scans of nucleotide diversity suggest positive selection on chromosome 2, 4, 5, 7, and 10 in durra sorghums, with successive adaptation during diffusion along the Sahel. Putative selective sweeps were identified, several of which colocalize with stay‐green drought tolerance (Stg) loci, and a priori candidate genes for photoperiodic flowering and inflorescence morphology. Genome‐wide association studies of photoperiod sensitivity and panicle compactness identified 35 and 13 associations that colocalize with a priori candidate genes, respectively. Climate‐associated SNPs colocalize with Stg3a, Stg1, Stg2, and Ma6 and have allelic distribution consistent with adaptation across Sahelian and Soudanian zones. Taken together, the findings suggest an oligogenic basis of adaptation to Sahelian versus Soudanian climates, underpinned by variation in conserved floral regulatory pathways and other systems that are less understood in cereals

Faye-Supporting_Information_File_S1

The file contains ADMIXTURE population structure at K = 3–7