Natural variability for protein digestibility and grain quality traits in a West African Sorghum Association Panel

Abstract

Sorghum is a staple crop and a major source of food and energy for developing countries in Africa and Asia. However, utilization of sorghum as human food is constrained by the low digestibility of its proteins after wet cooking, which could contribute to malnutrition, especially in sub-Saharan Africa. West Africa has a great diversity of sorghum landraces and improved cultivars yet analysis of genetic variation in protein digestibility remains unexplored. In this study, a collection of 385 sorghum accessions from Mali, Niger, Senegal, and Togo were assessed for protein digestibility, variation in grain composition, grain color, and presence or absence of a seed testa layer. In addition, genome-wide association studies were performed using 73,512 SNPs to assess genetic diversity in the collection and identify QTL for these traits. Analyses of grain composition showed that protein content ranged from 7% to 18%. Most of the accessions produced colored grain and 29% of the accessions exhibited a pigmented testa layer indicating presence of tannins. Tremendous variation in protein digestibility was detected among sorghum varieties and digestibility was negatively correlated with tannin content and grain color. The largest variability for protein digestibility was found in accessions from Niger with some accessions exhibiting protein digestibility values up to 53%, comparable to P721Q, a highly-digestible mutant created by chemical mutagenesis. GWAS identified 28 SNPs significantly associated with the seven studied traits. Some of these SNPs colocalized with previously reported QTL but other novel loci associated with grain quality traits were also reported.