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The Genetic Basis of Grain Traits in Sorghum
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Crop production must increase by 70% by 2050 in order to meet the expected requirements for population growth. While previous research has resulted in genetic improvement of the grain output in major cereal crops such as Zea mays and Oryza sativa, much less investment has been made to improve the grain yield of Sorghum bicolor, a drought-tolerant grain and forage crop native to Africa. Multiple genetic and environmental factors influence grain yield making it challenging to identify the pathways determining the amount of grain produced. In this dissertation, variation in grain yield, grain weight and grain number per plant, panicle architecture traits, and grain composition were measured in three different RIL populations. Several quantitative trait loci (QTL) for grain number and weight that act independently to modify grain yield were identified. QTL for for grain composition, stem hollowing, and nutrient remobilization were identified, a subset of which aligned with QTL for grain weight. A QTL on LG01 was identified for both grain weight and grain number in the BTx642 x Tx7000 recombinant inbred lines (RIL) population; however, the tradeoff between grain weight and grain number resulted in no increase in grain yield. In the BTx623 x IS3620c population, a QTL was identified in the same region on LG01 for grain yield and grain number. These results suggest that two tightly linked genes influencing grain weight and grain number are located in this region of LG01. Sorghum is a photoperiod-sensitive short-day plant with critical photoperiods ranging from 11-14 hours. When grain sorghum was introduced into more temperate climates, breeders selected for earlier flowering times to optimize grain yield. Six maturity loci, Ma₁-Ma₆, were identified that modify flowering time. When recessive, Ma₁– Ma₆ result in an earlier flowering phenotype in long days. Four of the six maturity genes, Ma₁, Ma₃, Ma₅ and Ma₆, have previously been map-based cloned and identified. In this study, Ma₂ was fine mapped, sequenced, and identified as Sobic.002G302700, a gene encoding a zinc finger transcription factor. The identified SNP in 80M creates a stop codon causing a loss of function of Ma₂.
Mattison, Ashley Jean (2017). The Genetic Basis of Grain Traits in Sorghum. Doctoral dissertation, Texas A & M University. Available electronically from