SORGHUM BIOMASS/FEEDSTOCK GENOMICS RESEARCH FOR BIOENERGY
- Texas A&M Agrilife Research
Objectives: The specific objectives of this project were to: (1) annotate genes, pathways and regulatory networks identified in the sorghum genome sequence that are important for biomass generation, and (2) identify, map and clarify the function of trait loci that modulate accumulation and quality of biomass in sorghum. Approach: Objective 1: Genes encoding proteins involved in biochemical pathways important for biomass generation and plant composition related to biofuel production (i.e., starch, lignin, sugar, cellulose and hemicellulose) were identified and projected onto biochemical pathways using the database MetaCyc (SorgCyc). The pathway projections provide a baseline of information on sorghum genes involved in biochemical pathways thus aiding our downstream analysis of QTL and traits. In addition, the information on sorghum biochemical pathways in Gramene can be readily compared to information on other cereals and other organisms via Gramene’s comparative mapping tools. This information helped identify gaps in the current knowledge of sorghum biochemistry and identified pathways and genes that may be useful to deploy in sorghum for biomass/bioenergy generation. Objective 2: Grain, biomass, and carbohydrate yields were measured in germplasm and a population consisting of 175 recombinant inbred lines (RILs) (F5:6) from the cross of BTx623 (a high yielding early flowering grain sorghum) × Rio (a high biomass sweet sorghum). Plant growth parameters were analyzed to obtain a baseline for downstream meta-analysis including plant height, flowering time and tillering, traits that likely modulate carbohydrate partitioning in various tissues and total biomass. Traits that affect grain yield, biomass (i.e. the tissue harvest index and distribution of grain, stem, and leaf weight), the composition of structural and non-structural carbohydrates, and the overall energy gain of the plant were evaluated. A genetic map of this population was created and QTL analysis will be carried out using QTL Cartographer. Results: As part of this project, our programs screened approximately 10,000 exotic sorghum accessions from the germplasm collection to identify specific lines with potential as an energy crop. Selection of specific lines was based on total biomass yield, strong photoperiod sensitivity, lodging resistance, and drought tolerance. Selection on these criteria resulted in lines that had high biomass yield, long duration of vegetative growth in temperate environments, with good low lodging and the ability to withstand periods of drought. Samples collected from this project (and others) were used to generate NIR calibration curves for structural composition of energy sorghums and sweet sorghums. These calibration curves were used for analysis of structural components in the recombinant inbred line population of BTx623 x Rio. A BTx623 x Rio recombinant inbred line population (grain x sweet sorghum) was evaluated for 28 traits related to grain and stem sugar yield and composition. Across three environments, a total of 145 QTL were identified. A small grain and stem sugar yield QTL tradeoff co-localized with a height and flowering time QTL on chromosome 9. A much larger tradeoff between grain and stem sugar yield co-localized under stress with flowering time locus ma1. More importantly, we were able to identify QTL that increased yield and altered the composition of stem sugar andthe genetic variance for stem sugar concentration did not co-localize with any grain trait QTL. These results suggest that total non-structural carbohydrate yield could be increased by selecting for major QTL from both sweet and grain sorghum types. We conclude that altering genetic potential for grain and stem sugar yield had greater impact on harvestable energy than altering grain and stem sugar composition. However, non-structural carbohydrate yield was more variable than stem sugar and grain composition traits due to biotic stress in some of our experimental locations. In addition to the analysis of non-structural carbohydrates, the genetic basis of leaf and stem structural biomass yield and composition in the same population was evaluated. For structural composition, a total of forty-one traits were evaluated and a total of 158 QTLs were identified across three locations. Many QTLs for structural and non-structural yield co-localized with loci for height, flowering time and stand density/tillering. QTLs 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. QTL and correlation coefficients suggest additional yield and composition loci exist that can be exploited to improve total energy without tradeoffs. In all studies, the results indicated that delayed flowering is critically important in high biomass cellulosic energy sorghum because the resulting long vegetative growth phase results in dramatically increased biomass accumulation and increases the plants’ tolerance to periods of drought that are encountered over the growing season. Genetic control of this photoperiod sensitivity is primarily based on the Ma5/Ma6 loci, which were mapped as part of this project. These genes, and markers associated with them are now being used as part of a marker-assisted breeding program to develop and produce photoperiod-sensitive bioenergy sorghum hybrids.
- Research Organization:
- Texas A&M Agrilife, College Station
- Sponsoring Organization:
- USDOE; USDOE EE Office of Biomass (EE-2E)
- Contributing Organization:
- Texas A&M University, Cornell University, Cold Spring Harbor Laboratory
- DOE Contract Number:
- FG02-06ER64306
- OSTI ID:
- 1122918
- Report Number(s):
- DOE - 492241
- Journal Information:
- Crop Science, Vol. 48, Issue 2008; ISSN 0011-183X
- Country of Publication:
- United States
- Language:
- English
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