GENOMIC STUDY AND GENETIC IMPROVEMENT OF SORGHUM [Sorghum bicolor (L) MOENCH] FOR HIGH PROTEIN DIGESTIBILITY
Sorghum is a staple crop and a major source of food and energy for the World’s developing countries. However, its utilization as human food is constrained by the low availability of its proteins after wet cooking which could lead to malnutrition especially in sub-Saharan Africa. West Africa has a great diversity of sorghum however, its study and use for improved protein digestibility remains unexplored. To provide knowledge on the characterization of West African sorghum germplasm for its exploitation in breeding programmes, a collection of 385 West African sorghum lines was assessed for seed quality, protein digestibility and anti-nutritional factors. Only 21% of the accessions were tannin-free, 56% had coloured seeds and protein content ranged from 9 to 18g/100g of samples. The largest variability for protein digestibility was found in accessions from Niger (1-55%). However, none of the lines of the entire collection was found to have high digestible proteins after wet cooking i.e. at least 60% digestibility hence raised the need to explore other sources for variability. Chemical mutagenesis, applied to seeds of BTx623, generated three ethyl methane sulfonate (EMS) mutants with 26 to 37% higher digestible proteins as well as 50 to 100% increase in lysine and 30 to 50% more tryptophan content than their wild type parent. Two of those mutants had invaginated protein body (PB) phenotype while the third mutant displayed a phenotype close to the wild type round PB. Further characterization of two mutants displaying contrasting PB phenotypes revealed that SbEMS3324 had more digestible proteins than P721Q while SbEMS1613 had harder seed kernels than P721Q, the first high digestible mutant generated in 1975. The increase in digestible proteins in the mutant with invaginated PBs was controlled by a single recessive allele and linked to a point mutation on a kafirin gene (Sobic.005G189000) in SbEMS3324.
However, in the mutant with round PBs, SbEMS1613, a missense mutation on a 26S proteasome PMSD10 subunit complex (Sobic.005G083340) located on chromosome 5 was causing the change in phenotype. Two pairs of SNP markers (ProF and ProR, KafF and KafR) were developed in this study and successfully shown to be linked to the genes causing the phenotype in each mutant. These primers could play a key role in accelerating the introgression of the high protein digestibility gene into locally-adapted sorghum varieties. Furthermore, to contribute to lower the humongous cost of wheat importation in Senegal as well as the use of maize in formulation of infant food and for poultry feeding, the Senegalese research institute developed white grained high yielding sorghum varieties well adapted to different environments in Senegal, however, these varieties lack the essential amino acid lysine and have poorly digested proteins. To increase their nutritional value, these varieties were crossed to a mutant with high digestible proteins, P721Q. One of the crosses, exploited in this study led to the development of 128 BC3F3 progenies generated from a cross between lowly digestible Faourou and P721Q that were evaluated at Bambey in Senegal during the rainy season 2017 along with the two parents. Amongst the 128 progenies, only 18 had high digestible proteins after wet cooking. Eight progenies outperformed the donor parent in terms of digestibility which could be explained by the combination of favourable alleles in those progenies known as transgressive segregation. The identified highly digestible individuals are potential varieties which would impact the food and feed industry in Senegal. It is recommended that they are tested for yield performance across environments for possible release in Senegal