Résumé
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.