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

KEY MESSAGE: Allele mining for provitamin A biofortification in sorghum is advanced with new pre-bred germplasm and markers that are trait-predictive in diverse germplasm and breeding programs. 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 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 SNPs associated with carotenoid variation, and validated their predictiveness in the six biparental families and diverse global germplasm. Two markers (snpSB00267 and snpSB00276), previously identified as zeaxanthin QTLs, were predictive of provitamin A content (β-carotene) in the biparental family evaluated and the diverse germplasm, and require further validation. Five markers that were predictive of zeaxanthin content-most notably snpSB00265, located within the zeaxanthin epoxidase (ZEP) gene; snpSB00277 and snpSB00264, near ZEP; and snpSB00279 and snpSB00280, in the β-carotene 3-hydroxylase gene-are recommended for indirect selection for provitamin A carotenoids. In a Senegalese breeding program, most markers (9 of 11) were segregating and contrasted for the elite germplasm (low carotenoid alleles) and yellow-endosperm donor lines (high carotenoid). Together, findings show that sorghum grain carotenoids can be increased through breeding, and demonstrate the potential of marker-assisted selection for provitamin A biofortification.