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Genetic improvement of sorghum [Sorghum bicolor (L.) Moench] has traditionally focused on a single nonstructural carbohydrate, either grain starch or stem sugar. Sorghum starch and sugar may both be used as feedstocks for biofuel production. To investigate genetic tradeoffs between grain and stem sugar, a population derived from sweet sorghum cultivar Rio and grain sorghum 'BTx623' was evaluated for 27 traits related to grain and stem sugar yield and composition. Across three environments, a total of 129 quantitative trait loci (QTL) were identified. Tradeoffs identified between grain and stem sugar yield QTL colocalized with height and flowering time QTL. Most importantly, QTL were identified that increased yield and altered the composition of stem sugar and grain without pleiotropic effects. For example, a QTL on chromosome 3 that explained 25% of the genetic variance for stem sugar concentration did not colocalize with any grain QTL. These results suggest that total nonstructural carbohydrate yield could be increased by selecting for major QTL from both grain and sweet sorghum types. We conclude that altering grain and stem sugar genetic potential for yield traits should lead to greater feedstock improvement than altering composition traits.

Digestion and fermentation of lignocellulosic biomass (i.e., structural carbohydrates) are predicted to deliver higher yields of energy per hectare than sugar and starch (nonstructural carbohydrates), yet little research on genetic variation in crop feedstock biomass traits has been conducted. We investigated the genetic basis of leaf and stem biomass yield and composition in a population derived from a high-biomass sweet sorghum, 'Rio', and a grain sorghum inbred line, 'BTx623', and compared these results with those from analyses of grain and stem sugar traits that we reported previously. Thirty-one traits were evaluated and a total of 110 quantitative trait loci (QTL) were identified across three locations. Many QTL for structural and nonstructural carbohydrate yields colocalized with loci for height, flowering time, and stand density--tillering. Quantitative trait loci for composition had little colocalization across tissues and environments. Separate genetic control for leaf and stem structural carbohydrate composition was identified, as well as separate genetic control of protein accumulation in leaf, stem, and grain. To maximize energy yields from grain and dedicated biomass sorghums, results suggest yield traits should be targeted for improvement before composition traits.

Graphical genotypes have been generated for o set of sorghum [Sorghum bicolor (L.) Moench] germplasm, which includes selected public inbreds, germplasm from the world collection, and ancestral lines central to the early breeding efforts of sorghum. We have focused our present examination on sorghum chromosome SBI-06, which encodes [ma.sub.1] and [dw.sub.2], two genes critical to sorghum improvement dating to the original introduction of tropical sorghums into the United States. Utilizing the pedigree relationship between sorghum cultivars, the patterns of genetic variation were detailed within segmental chromosomal blocks of SBI-06. Segmental genomic blocks were traced back through multiple generations of a pedigree, often back to founder tropical accessions. The graphical genotypes reveal genomic signatures of historical breeding decisions, especially evidence of directional selection during the conversion of tropical accessions to temperate adaptation. This information is central to our efforts to understand those crop improvement processes that have shaped the genomic diversity of elite sorghum cultivars.

The objectives of this study were (i) to assess the level of genetic diversity in elite sterility-maintaining (B) and fertility-restoring (R) sorghum [Sorghum bicolor (L.) Moench] lines as compared with a group of exotic and converted germplasm (IS) from the World Collection, (ii) to compare the classification of germplasm on the basis of estimates of genetic similarities obtained by means of AFLP and microsatellite (SSR) markers, and (iii) to compare the classification of germplasm obtained by different classes of molecular markers. A set of 100 SSRs, 1318 EcoRI/MseI AFLP, and 496 PstI/MseI AFLP markers with known map positions were utilized to determine the genetic similarity in a group of B, R, and IS public inbreds. Cluster analysis of genetic similarity estimates (G[S.sub.ij]) revealed that the classification of sorghum inbreds is based on the sorghum working groups, Zera-zera, Kafir, Kafir-Milo, Durra, and Feterita. Cluster analyses failed to give a clear differentiation between B- and R-lines, suggesting that R- and B-lines do not represent well-defined heterotic groups in this set of public lines. By comparing the different classes of molecular markers (SSRs, AFLPs, combinations of SSRs and AFLPs), we determined that the distribution of the markers and the coverage of the genome by the markers did affect the classification of genotypes. Dendrograms of genetic similarity (GS) based on PstI/MseI AFLP markers, or a set of markers spaced at 1- to 2-cM intervals across the genome, produced clusters that were in better agreement with pedigree information than the analysis based solely on the EcoRI/ MseI AFLP or SSR markers used in this study., SORGHUM is native to Sub-Saharan Africa and has been cultivated for centuries as a staple cereal grain in much of Asia and Africa. Sorghum became economically important in the semiarid [...]

Population trends predict increasing food needs while progress in developmental and genomic plant sciences offer new opportunities for crop improvements. The grass-based grain crops have a high degree of synteny in their genomes, thus raising the possibility of using specific information more broadly. Studies of Sorghum bicolor (L.) Moench are beginning to link physiological behavior to specific genes and hormone-based regulatory systems in ways that suggest specific strategies for improvement. Findings from several other grasses are adding to the pool of information being derived from Sorghum. This information relates to flowering and floral development, maturity and senescence, temperature effects via the biological clock, shade avoidance behavior, apical dominance, shoot elongation, and root development including constitutive aerenchyma formation. These studies, along with others, offer a number of options for conventional plant breeding and genetic transformations to improve grass-based crops and satisfy part of the projected human food needs of coming decades., THANKS IN LARGE PART to the Green Revolution, world food supplies are adequate for the current population of the earth. However, projections of population growth extend the earth's current 6.0 [...]

Graphical genotypes hove been generated for a set of sorghum [Sorghum bicolor (L.) Moench] germplasm, which includes selected public inbreds, germplasm from the world collection, and ancestral lines central to the early breeding efforts of sorghum. We have focused our present examination on sorghum chromosome SBI-06, which encodes ma1 and dw2, two genes critical to sorghum improvement dating to the original introduction of tropical sorghums into the United States. Utilizing the pedigree relationship between sorghum cultivars, the patterns of genetic variation were detailed within segmental chromosomal blacks of SBI-06. Segmental genomic blocks were traced back through multiple generations of a pedigree, often back to founder tropical accessions. The graphical genotypes reveal genomic signatures of historical breeding decisions, especially evidence of directional selection during the conversion of tropical accessions to temperate adaptation. This information is central to our efforts to understand those crop improvement processes that have shaped the genomic diversity of elite sorghum cultivars. [ABSTRACT FROM AUTHOR]