Date of Award

12-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Genetics

Committee Member

Dr. Stephen Kresovich, Committee Chair

Committee Member

Dr. Leigh Anne Clark

Committee Member

Dr. John Mueller

Committee Member

Dr. Rajandeep Sekhon

Abstract

Farming begins with a seed, and having the proper genetics within that seed to match the environment and management practices is critical. Plant breeders can be more effective at tailoring crop cultivars and hybrids when the genetic mechanisms of key traits are understood. The scope of this study was to investigate the natural diversity, genetic regions, and individual genes that are associated with components of grain yield and quality in sorghum [Sorghum bicolor (L) Moench]. These traits were characterized in different environments, years, and populations to observe the variation and interactions that exist and allow for genome-wide association studies (GWAS) and QTL mapping to detect marker-trait associations. Overall, there was high variation for most grain yield and quality traits in a diverse panel of 390 sorghum accessions and in two recombinant inbred line (RIL) populations. Grain number per primary panicle (GNP) contained the greatest variation at nearly 34-fold while gross energy (kcal g-1) was lowest at 1.1-fold. The heritability of GNP was much lower than the heritability of 1000-grain weight (TGW) although GNP variation was primarily under genetic control. All five grain quality traits under study also displayed moderate to high heritability. No QTLs identified by GWAS for GNP and TGW co-located to suggest the two yield components are under independent genetic regulation, which provide targets to potentially reduce the trade-off observed between these traits. Marker-trait associations for TGW were identified on chromosome 1 within or near RCD1, a gene primarily expressed in the developing seed. Sequencing of RCD1 showed haplotypes correlated strongly with differences in grain weight. Major effect QTLs for starch, protein, fat, and gross energy were identified to provide targets for sorghum grain quality improvement. QTL analysis for amylose content was able to fine map the known Wx locus to just 12 kilobases using a high-density SNP dataset. GWAS and QTL mapping both detected a strong crude fat QTL on chromosome 10 near the candidate gene DGAT1 that is important in maize lipid biosynthesis. Some grain quality QTLs found in a RIL population co-located with QTLs for grain yield components to suggest pleiotropic effects may exist in sorghum.

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