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Abstract
With increasing energy demand and diminishing petroleum reserves, energy sources derived from renewable plant-based biomass are an attractive substitute for fossil fuels. Being the fifth most widely grown cereal crop in the world, sorghum is among one of the most attractive bioenergy feedstocks currently under active study. In this thesis, we provide a valuable addition to the genetic resources of sorghum by describing a recombinant inbred line (RIL) population of 161 F5 genotypes for the widest euploid cross that can be made in eusorghums, of annual S. bicolor x perennial S. propinquum. It offers advantages over early-generation populations of this cross that will shed new light on genetic, environmental, and physiological / biochemical factors that regulate plant growth and development. A combination of linkage and association genetic approaches using a S. bicolor x S. propinquum F2 population, a S. bicolor BTx623 x IS3620c RIL population, and a S. bicolor diversity panel of 354 accessions characterized at 265,487 SNPs allows us to: tentatively identity and characterize the D gene for the dry trait; and determine genomic regions corresponding to 3 stem diameter traits and 2 water content traits. We also revealed the evolutionary path of the D gene, as having evolved under balancing selection during a recent tandem expansion of the BGLU gene family in sorghum after its divergence from maize. Co-localizations of stem diameter and water content traits with a number of other bioenergy traits, including plant height, flowering time, branching, stem volume and the dry trait, were also observed, suggesting that their inheritance may be functionally (pleiotropy) or physically (linkage disequilibrium) linked. Increasing knowledge of the genetic control of these bioenergy traits in sorghum, and in identification of corresponding genes and their functions, may lead to tools and strategies for either enhancing or suppressing these traits, supporting advances toward greater use of plant-based biomass in biofuel production.