Genetic structure of the sorghum accession panel
Striga resistance is more prevalent in sorghum landraces from SSA because of co-evolution of the host and the pathogen (Bellis et al. 2020). Analysis of the geo-referenced origin of the SAP showed a notable overlap with Striga distribution range in SSA (Figure 1a and b). Further, the SAP was genetically diverse with representation from all the major races and subraces of sorghum. The most common race was caudatum and its subraces having 122 accessions with collections mostly from Africa. Durra was also common with 79 collections from eastern Africa and India. The least common race was bicolor with 10 accessions collected from eastern Africa (Figure S1a). To understand the genetic structure of the SAP, we carried out population structure analysis. We used both phylogenetic relationships and hierarchical Bayesian clustering (HBC) to provide information on sorghum race structure. In general, most races formed clusters based on their races rather than geographical status as revealed by phylogenetic analysis (Figure 1c). HBC further resolved the genetic structure of the SAP. At the most likely K value (K=7) HBC grouped the panel into 5 distinct clusters of durra, bicolor, guinea, caudatum and kafir caudatum. The rest of the population was an admixture suggestive of multiple race integrations in the development of the panel (Figure S1b). Based on genetic diversity, and high representation from SSA, we determined that the SAP collection was a good resource for Striga resistance allele mining.