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INVESTIGATOR: Rhodes, D. H.

PERFORMING INSTITUTION:
AGRICULTURAL RESEARCH SERVICE
BROOKINGS, SOUTH DAKOTA 57006

DEVELOPMENT OF MOLECULAR BREEDING RESOURCES FOR INCREASED GRAIN CAROTENOIDS IN SORGHUM

NON-TECHNICAL SUMMARY: Carotenoids are red, yellow, and orange plant pigments-such as the orange beta-carotene in sweet potatoes and the red lycopene in tomatoes-that are involved in photosynthesis and protection against oxidative stress. In humans, dietary carotenoids act as precursors to vitamin A, as well as antioxidant and anti-inflammatory compounds, protecting against a myriad of diseases, including cancer, cardiovascular disease, and age-related macular degeneration. Cereals are generally poor sources of carotenoids compared to fruits and vegetables, but since cereals make up the majority of the human diet an increase in cereal carotenoids could have a significant impact on human nutrition. Sorghum is one of the world's largest produced cereal crops and a staple food for millions of people in semi-arid regions of sub-Saharan Africa and Asia. In the United States, it is primarily used in animal feed, but is increasingly used in specialty food products, especially those that are gluten free. Efforts to improve the nutritional quality of sorghum grain have relied primarily on traditional plant breeding, a process that can take years before a line is ready to be released. Marker-assisted breeding (the use of genetic markers to select for a trait of interest in crop breeding) can vastly accelerate the development of biofortified crops.The ultimate goal of this research is to provide genetic tools that will help breeders rapidly develop high-carotenoid sorghum varieties. To this end, we will quantify grain carotenoid concentrations in hundreds of sorghum lines using high-performance liquid chromatography (HPLC), a gold-standard technique for quantifying compounds. Since HPLC is a time-consuming and expensive technique, we will develop a high-throughput method for measuring carotenoid concentrations using near-infrared spectroscopy, a technique that predicts the concentration of a compound by reflecting near-infrared light on the whole grain. We will identify the genomic regions containing genes that control carotenoid concentrations using a genome-wide association study (GWAS), a method that scans the genome for associations between carotenoid concentrations and variations in single nucleotides. Finally, we will identify the nucleotide variations responsible for carotenoid variation by sequencing candidate genes that were identified through GWAS. The allelic variants can then be used as markers for marker-assisted breeding to develop high-carotenoid sorghum varieties that will benefit human health.

OBJECTIVES: The major goals of this project are to find new sources of high carotenoid sorghum and develop carotenoid genetic markers for usein marker-assisted breeding. Objectives are as follows:Characterize the natural variation in sorghum grain carotenoids in a largediverse panel using HPLC and colorimetry.Develop a high-throughput method of measuring sorghum grain carotenoids bycreating NIRS equations to predict carotenoid content.Identify QTL underlying natural variation of sorghum grain carotenoids usingGWAS.Validate NIRS calibration equations by comparing HPLC and NIRS on abiparental breeding population.Confirm GWAS QTL by conducting linkage mapping on a biparental breedingpopulation.Identify functional allelic variants at candidate genes.