Résumé
Sorghum is considered like a rainfed crop but it is also grown in the dry season: direct sowing in northern Senegal and transplanted after approximately 45 days of growth in the nursery in the Lake Chad Basin. The genetic diversity of these varieties of sorghum is not well known, the objective of this study is therefore to evaluate this diversity of rainfed sorghum and dry season sorghum collected in Senegal and in the Lake Chad Basin and to understand its organization. The plant material studied includes 153 accessions covering 4 eco-seasonal types of sorghum defined on the basis of seasonality (rainy season, dry season) and eco-geographical zone (Senegal and Lake Chad Basin). High-throughput sequencing data (GBS) made it possible, on the basis of approximately 120,000 SNPs covering the sorghum genome, to describe the genetic diversity of the collection studied in relation to the 4 eco-seasonal types. The genetic diversity of each population was estimated by evaluating its number of total alleles, its number of private alleles and its allelic richness. Principal component analysis was carried out to study the organization of the genetic diversity of the global population. The genomic analysis showed that the diversity of the 153 sorghum accessions is structured into 3 genetic groups. This organization of the diversity reflects the influence of seasonality and geographical origin of sorghum accessions. Two-thirds of dry season sorghum accessions in the Lake Chad Basin form a welldifferentiated group from rainfed sorghum accessions. These experimental results provide new directions for integrating dry season sorghum diversity into sorghum improvement programs.