Advancing provitamin A biofortification in sorghum: From allele mining and marker development to prebreeding and breeding

Abstract Provitamin A biofortification of the staple cereal crop sorghum (Sorghum bicolor [L.] Moench) could reduce vitamin A deficiency in low-income countries of sub-Saharan Africa. To advance the mining of alleles that confer high provitamin A from genebank accessions, we developed prebreeding germplasm and trait-predictive markers, and established the utility of these markers in a range of prebreeding and breeding materials. We first tested the hypothesis that carotenoid concentrations in sorghum grain can be increased through breeding using six biparental families developed from high-carotenoid genebank accessions. The families exhibited abundant transgressive segregation for carotenoid concentrations, with positive asymmetry in many cases (4 of 6 families) suggesting the release of epistatic variation. Next, we developed eleven markers from single nucleotide polymorphisms associated with carotenoid variation, and validated them in the biparental families and diverse global germplasm. Each of the markers was associated with total carotenoid content, lutein, zeaxanthin, and β-carotene in the families and diverse global germplasm tested (most notably snpSB00265 located within zeaxanthin epoxidase [ZEP] genes; snpSB00277 and snpSB00264 near ZEP; and snpSB00279 and snpSB00280, in the β-carotene 3-hydroxylase gene). In a Senegalese breeding program, most of the markers (9 of 11) are contrasting for the elite germplasm (low carotenoid alleles) and yellow-endosperm donor lines (high carotenoid). Together the findings show that sorghum grain carotenoids can be increased through breeding, and demonstrate the potential of marker-assisted selection for provitamin A biofortification.