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Browsing by Author "Morris, Geoff, committee member"

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    Characterizing controls of sorghum carotenoid bioaccessibility for vitamin A biofortification
    (Colorado State University. Libraries, 2024) McDowell, Rae, author; Rhodes, Davina, advisor; Morris, Geoff, committee member; Chaparro, Jacqueline, committee member
    Vitamin A deficiency is one of the leading causes of preventable blindness globally and can lead to decreased immune function and mortality. Sorghum bicolor is consumed in areas that are affected by vitamin A deficiency, where biofortification of sorghum may be a way to address these nutritional deficiencies. However, sorghum breeders do not know the target breeding value for provitamin A carotenoids or the best breeding strategy for carotenoid biofortification. Bioaccessibility—the amount of a nutrient available to be absorbed in the gut—can be reduced by a variety of factors, and needs to be determined in order to define a biologically relevant target value of provitamin A carotenoids. Additionally, genetic controls of grain bioaccessibility need to be determined in order to develop breeding tools. This research sought to develop biofortification breeding strategies by characterizing the environmental and genetic controls of carotenoid bioaccessibility through genomic mapping and multi-environment trials. We hypothesized that 1) genotype has a greater impact on variation in carotenoid bioaccessibility than genotype by environment interactions, and 2) carotenoid bioaccessibility is an oligogenic trait. To test these hypotheses, twelve sorghum genotypes were grown across three climates (semi-arid, humid-subtropical, and humid-continental) for two years. Results suggest there is a strong environmental and genotype by environment interaction in the regulation of bioaccessibility of sorghum carotenoids. One environmental factor that may contribute to variation in bioaccessibility is iron and zinc content, which was found to have a significant negative correlation with carotenoid bioaccessibility traits. Next, genome-wide association studies (GWAS) in a diverse population and linkage mapping in a F5.6 recombinant inbred family identified a handful of genes or regions underlying variation in carotenoid bioaccessibility and carotenoid content, supporting the hypothesis that there are oligogenic controls. GWAS revealed two significant marker trait associations (MTAs) underlying relative bioaccessibility of ɑ-cryptoxanthin and cis-β-carotene on chromosomes five and one respectively. Furthermore, in the inbred family, there were observations of transgressive segregation, in which a portion of the progeny exceeded parental means for both carotenoid content and bioaccessibility. Additionally, linkage analysis identified six unique regions for carotenoid content and three unique regions for carotenoid bioaccessibility, further supporting the oligogenic hypothesis for genetic architecture. Linkage analysis also revealed colocalization of regions between carotenoid content and carotenoid bioaccessibility, either suggesting co-regulation or linkage between traits. Interestingly, several a priori candidate genes in proximity to identified MTAs and linkage regions were broadly involved in carbohydrate, lipid, and carotenoid metabolism. These results will help refine the carotenoid biofortification target value and lead to the development of molecular breeding tools that can be used to increase carotenoid content and bioaccessibility, as well as to maintain favorable alleles, in sorghum breeding germplasm.