Genetic, agronomic and compositional characterization of brown midrib sweet sorghum lignocellulosic biomass for ethanol production
Sorghum is a promising bioenergy crop due to its unique phenotypic and genotypic attributes. Quality (low lignin and high stem sugar concentration) and quantity (biomass yield, plant height, plant maturity, etc.) biomass traits are key contributors to ethanol yield and production. In this study, a 236 sorghum recombinant inbred line (RIL) population was subjected to genetic, agronomic and compositional characterization for ethanol yield and production. We found that the sweet mutation enhances biomass quantity traits in the RILs which translates to higher ethanol production and biomass quality which improves ethanol yield. The variance components showed from moderate to high heritability for biomass quantity and quality traits. The variability observed in most of these traits was due mainly to genetic effects. Correlations showed positive associations between biomass quantity traits and stem sugar concentration (SSC). These results indicate that selection for multiple traits could increase ethanol production. Single marker analysis showed two possible quantitative trait loci, on chromosomes 6 and 7, explaining only 2 and 7% of the variation in SSC measurements. The brown midrib mutation in this population was previously identified in the caffeic acid-O-methyltransferase (COMT) gene resulting in reduced lignin content. A useful InDel marker for the mutant allele of COMT was identified for this population. Fiber detergent analysis (FDA) was performed to estimate the amount of hemicellulose, cellulose and lignin. Glucose recovery and theoretical ethanol yield and production were calculated and differences among grouped RILs analyzed. Only RILs carrying the brown midrib mutation showed significantly higher glucose recovery, those carrying both compositional mutations, showed significantly higher ethanol yields, and those with double mutations or the sweet mutation had significantly higher theoretical ethanol production. Lignin (R2= 0.66) was identified as the most reliable predictor for glucose recovery. Lignin and SSC (R2= 0.46 and 0.35, respectively) were identified as good predictors for ethanol yield. Dry stover and fresh stover yield (R 2= 0.89) were the most appropriate predictors for ethanol production. Additionally, a nitrogen experiment was conducted to study the effect of four nitrogen rates on biomass traits of nine sorghum varieties, as lines and hybrids with and without brown midribs, a sweet and a photoperiod sensitive cultivar and a maize hybrid. Nitrogen application rate had significant effects on biomass components. The grain sorghum hybrid and the grain maize hybrid maximized grain yields across nitrogen rates. The photoperiod sensitive and sweet sorghums maximized stover yields across nitrogen rates. Maximum grain yield was obtained at 135kg N ha-1, while maximum stover yield was 67kg N ha-1. Across genotypes, grain nitrogen use efficiency (NUE) ranged from 19 to 50kg kg-1, while stover NUE ranged from 31 to 125kg kg-1. The dual-purpose sorghum hybrid showed the highest grain NUE, while the sweet sorghum showed the highest stover NUE. This research suggests that targeted improvement of biomass quantity and quality traits, and nitrogen management could increase ethanol production.
Ejeta, Purdue University.
Agronomy|Alternative Energy|Genetics|Plant sciences
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