Sweet sorghum as biofuel feedstock: recent advances and available resources

Crop Science, 2008

T here is renewed interest in using sugars derived from agricultural crops as feedstocks for biofuel production (Farrell et al., 2006; USDOE, 2006; Somerville, 2007), large-scale manufacture of more complex molecules (Lichtenthaler and Peters, 2004), and in planta syntheses of harvestable biomolecules (i.e., nutraceuticals) (Mazur et al., 1999; Mohanty et al., 2002). Improving a species for use as biofuel feedstock requires a change in perspective: crops must be regarded as living systems for capturing and storing energy rather than simply as a sole source of food, feed, or fi ber products. This changes the basic biological question from "how much of a crop's energy can be converted into food?" to "how can we maximize the total useable energy that can be produced and stored throughout the growing season?". Furthermore, characterization and quantifi cation of environmental and postharvest energy degradation in addition to genetics will be crucial for developing economically feasible biofuel feedstocks.

During recent years, sorghum has drawn intensive attention from the scientific community and policy decision-makers. Three categories of sorghum, grain, forage, and sweet sorghum can be used differently for producing bioethanol and other kinds of biofuels. While grains from grain sorghum and juice from sweet sorghum are readily fermentable, the sorghum stalk which is a lignocellulosic material is recalcitrant. To utilize sorghum as a bioenergy crop, however, the biomass quality and yield must be enhanced. Highly fermentable and highly digestable lines are extremely desirable but research on this aspect is lagging behind those of other crops, such as maize. With numerous genes affecting sorghum quality being known, it is reasonable to expect that sorghum can be improved to serve as a biomass plant well through genetic and molecular breeding. Over the years, genetic modification of sorghum has been mainly conducted in three areas: 1) reducing lignin content by establishing brown midrib mutants and understanding the genetic mechanisms for lignin reduction; 2) developing cold tolerant progenies and identifying quantitative trait loci (QTL) related to cold tolerance; and 3) investigating sugar related traits with the aim of increasing contents of sugar and nonstructural carbohydrates. This review provides detailed information on how these studies are carried out. Future research directions are also recommended for transforming sorghum from a promising crop to a truly invaluable plant in the biofuel arena.

ifeu.org, 2002

Geopolitical tensions in some oil producing regions and the uncertainties surrounding the future availability of fossil fuels, as well as the urgent necessity to mitigate negative impacts on climate through reduced CO 2 emissions, have created a strong interest for biofuels. Among potential crops for the production of biofuels, sorghum is an interesting C4 plant, able to combine production of food and fuel as well as a variety of other products. However, new ideotypes of sorghum need to be defined in order to optimise efficiency with respect to the following three potential use options of sorghum: (1) production of ethanol through second generation processes, (2) production of first generation ethanol combined with the use of bagasse for co-generation, and (3) production of first generation ethanol combined with the production of grain and the use of bagasse as fodder. This paper presents results elaborated in the framework of the project SWEETFUEL, supported by the European Commission, on the successful combination of traits of new sorghum ideotypes suitable for the three abovementioned use options.

Advances in Biofuels and Bioenergy, 2018

Nonrenewable energy resources deplete with the passage of time due to rapid increase in industrialization and population. Hence, countries worldwide are investing dearly in substitute energy resources like biofuel from miscellaneous set of feedstocks. Among the energy crops, sorghum serves as a model crop due to its drought tolerance, small genome size (730 Mb), high biomass, dry matter contents, quick growth, wide adaptability to diverse climatic and soil conditions and C4 photosynthesis. Sweet sorghum with high sugar content in stalk is an efficient feedstock for advanced biofuels and other bio-based products from sugars. However, high biomass sorghum has the utility as a feedstock for cellulosic biofuels. The enhanced yield of monomeric carbohydrates is a key to cheap and efficient biofuel production. The efficiency of lignocellulosic biofuels is compromised by recalcitrance to cell wall digestion, a trait that cannot be efficiently improved by traditional breeding. Therefore, scientists are looking for solutions to such problems in biomass crop genomes. Sorghum genome has been completely sequenced and hence this crop qualifies for functional genomics analysis by fast forward genetic approaches. This chapter documents the latest efforts on advancement of sorghum for biomass potential at morphological and molecular level by exploiting genomics approaches.

PloS one, 2017

Sweet sorghum [Sorghum bicolor (L.) Moench] is a type of cultivated sorghum characterized by the accumulation of high levels of sugar in the stems and high biomass accumulation, making this crop an important feedstock for bioenergy production. Sweet sorghum breeding programs that focus on bioenergy have two main goals: to improve quantity and quality of sugars in the juicy stem and to increase fresh biomass productivity. Genetic diversity studies are very important for the success of a breeding program, especially in the early stages, where understanding the genetic relationship between accessions is essential to identify superior parents for the development of improved breeding lines. The objectives of this study were: to perform phenotypic and molecular characterization of 100 sweet sorghum accessions from the germplasm bank of the Embrapa Maize and Sorghum breeding program; to examine the relationship between the phenotypic and the molecular diversity matrices; and to infer about...

Biotechnological Applications of Biomass

Sorghum is one of the main cereal crops, its consumption is large, since it provides grain, fiber and biofuel. Likewise, its genome, with only 10 diploid chromosomes, makes it an attractive model for research and genetic improvement. Sorghum is the most studied C4 plant of its genus; several lines have been developed under three main characteristics: grain, forage and sugar biomass. Compared to other crops, sweet sorghum possesses high levels of highly fermentable sugars in the stem. Also, it has the ability of producing high production yields in marginal lands. These characteristics make it and attractive crop for the generation of biofuels. Molecular markers associated to several resistances and tolerances to biotic and abiotic factors have been described in literature. These allow the development of high-density linkage maps, which, along with the rising availability of sorghum genomes, will accelerate the identification of markers and the integration of the complete genome seque...

2018

Sweet Sorghum [Sorghum bicolor (L.) Moench] is a type of cultivated sorghum grown primarily for its sugar-rich stalks. Because of its high fermentable sugar content, the crop is widely recognized as an alternative feedstock source for bio-fuel production. The extent to which stalk sugar accumulation occurs may be determined by several factors including the sink size. Grain is the most important sink in sorghum and other grain crops. Three experiments were conducted in this study to determine the extent to which the grain sink can reduce sugar accumulation in the stalks, to test and validate a genetic system that allows development of sterile sweet sorghum hybrids, and to assess the potential of sugar-rich hybrids to overcome stalk rot diseases. The first experiment, based on 22 sweet sorghum genotypes, was undertaken to study the effect of eliminating the grain sink (removing the head prior to anthesis) on stalk juice yield, sugar accumulation, and biomass. The data showed that the ...

Journal of Experimental Botany, 2021

Sorghum [Sorghum bicolor (L.) Moench] is the fifth most important cereal crop globally by harvested area and production. Its drought and heat tolerance allow high yields with minimal input. It is a promising biomass crop for the production of biofuels and bioproducts. In addition, as an annual diploid with a relatively small genome compared with other C4 grasses, and excellent germplasm diversity, sorghum is an excellent research species for other C4 crops such as maize. As a result, an increasing number of researchers are looking to test the transferability of findings from other organisms such as Arabidopsis thaliana and Brachypodium distachyon to sorghum, as well as to engineer new biomass sorghum varieties. Here, we provide an overview of sorghum as a multipurpose feedstock crop which can support the growing bioeconomy, and as a monocot research model system. We review what makes sorghum such a successful crop and identify some key traits for future improvement. We assess recent...

G3: Genes, Genomes, Genetics, 2020

In sorghum [Sorghum bicolor (L.) Moench], hybrid cultivars for the biofuel industry are desired. Along with selection based on testcross performance, evaluation of the breeding population per se is also important for the success of hybrid breeding. In addition to additive genetic effects, non-additive (i.e., dominance and epistatic) effects are expected to contribute to the performance of early generations. Unfortunately, studies on early generations in sorghum breeding programs are limited. In this study, we analyzed a breeding population for bioenergy sorghum, which was previously developed based on testcross performance, to compare genomic selection models both trained on and evaluated for the per se performance of the 3 rd generation S 0 individuals. Of over 200 ancestral inbred accessions in the base population, only 13 founders contributed to the 3 rd generation as progenitors. Compared to the founders, the performances of the population per se were improved for target traits. The total genetic variance within the S 0 generation progenies themselves for all traits was mainly additive, although non-additive variances contributed to each trait to some extent. For genomic selection, linear regression models explicitly considering all genetic components showed a higher predictive ability than other linear and non-linear models. Although the number and effect distribution of underlying loci was different among the traits, the influence of priors for marker effects was relatively small. These results indicate the importance of considering non-additive effects for dissecting the genetic architecture of early breeding generations and predicting the performance per se. KEYWORDS sorghum genomic prediction Bayesian alphabet breeding population GWAS GenPred Shared data resources Sorghum [Sorghum bicolor (L.) Moench] is a promising bioenergy crop (Regassa and Wortmann 2014). Commercial F 1 hybrid sorghums for biofuel production need to exhibit superiority in multiple traits, such as biomass, sugar content, and stress tolerance. In hybrid breeding, testcrosses are generally used to evaluate progeny performance. Many studies have focused on the relationship between the performance of partially or completely inbred lines and their testcrosses to a common unrelated tester to predict the effectiveness of selection on line per se performance for improving testcross performance. In maize, the correlation between line per se and testcross performance was intermediate to high for some traits, but small for grain yield (Mihaljevic et al. 2005). Similarly, other studies in maize and rye revealed that the correlations between phenotypes measured in lines per se and their testcrosses were often small for complex traits (Bekavac et al. 2008; Falke et al. 2010; Miedaner et al. 2014). Although the breeding value of lines or individual breeding candidates for testcross performance is the most important selection criterion in hybrid breeding, the characteristics of the per se are also considered because they impact the efficiency of F 1 seed production. For example, dwarf genotypes, which are easier to handle and more resistant to lodging than taller ones, are often utilized as the seed

G3 Genes|Genomes|Genetics, 2021

During the past decade, sweet sorghum (Sorghum bicolor Moench L.) has shown great potential for bioenergy production, especially biofuels. In this study, 223 recombinant inbred lines (RILs) derived from a cross between two sweet sorghum lines (Brandes × Wray) were evaluated in three trials. Single-nucleotide polymorphisms (SNPs) derived from genotyping by sequencing of 272 RILs were used to build a high-density genetic map comprising 3,767 SNPs spanning 1,368.83 cM. Multitrait multiple interval mapping (MT-MIM) was carried out to map quantitative trait loci (QTL) for eight bioenergy traits. A total of 33 QTLs were identified for flowering time, plant height, total soluble solids and sucrose (five QTLs each), fibers (four QTLs), and fresh biomass yield, juice extraction yield, and reducing sugars (three QTLs each). QTL hotspots were found on chromosomes 1, 3, 6, 9, and 10, in addition to other QTLs detected on chromosomes 4 and 8. We observed that 14 out of the 33 mapped QTLs were fo...