Opportunities and roadblocks in utilizing forages and small grains for liquid fuels

Authors: Sarath, Gautam; Mitchell, Robert - Rob; Sattler, Scott; Funnell-Harris, Deanna; Pedersen, Jeffrey; Graybosch, Robert; Vogel, Kenneth

Submitted to: Journal of Industrial Microbiology and Biotechnology
Publication Type: Review Article
Publication Acceptance Date: 12/3/2007
Publication Date: 5/1/2008
Citation: Sarath, G., Mitchell, R., Sattler, S.E., Funnell-Harris, D.L., Pedersen, J.F., Graybosch, R.A., Vogel, K.P. 2008. Opportunities and roadblocks in utilizing forages and small grains for liquid fuels. Journal of Industrial Microbiology and Biotechnology 35: 343-354.

Interpretive Summary: Generating liquid fuels from plant sources will be a key to meeting mandated goals for transportation and lowering imports of oil. In order to meet these goals, many different types of plants will be required. Forages such as switchgrass and sorghum and small grains such as wheat and sorghum represent alternate sources of herbaceous feedstocks for the nascent biofuels sector. Opportunities therefore exist to develop strategies that can enhance breeding, agronomy and management of these crops as sources of biofuels. This review focuses on the potential advantages and disadvantages of these species as feedstocks and highlights the synergy provided by applying what is known from forage digestibility studies to the biofuels sector.

Technical Abstract: Forages and small grains represent unique and potentially sustainable feedstocks for the nascent biomass fuels sector. Biorefineries will require feedstocks of the required quality on a year-around basis. Opportunities exist to enhance crops such as switchgrass, sorghum and wheat as sources of biomass via improved genetics and agronomics, in contrast to cereal crops which have been selected for grain yield for a considerable length of time, switchgrass has been bred for improved yield, forage quality, and other traits for a relatively short (~50 years) time frame and still retains tremendous exploitable genetic diversity. From a crop perspective, switchgrass (Panicum virgatum) can be specifically improved to fit a particular agronomic, management, and conversion platform. Combined with emerging studies on switchgrass genomics, conversion properties and management the future for genetic modification of this species through conventional and molecular breeding strategies appear to be bright. Although, wheat (Triticum aesitvum) and sorghum (Sorghum bicolor) with improved starch content and composition could be developed for use in starch-based conversion systems the use of wheat for this purpose is unlikely but its research use on the effect of starch properties on biofuel yield is likely. Forage and sweet sorghums, and wheat crop residue could be harvested for biomass. The presence of brown-midrib mutations in sorghum that alters cell wall composition by reducing lignin will likely be of value for biomass conversion to ethanol. These and other attributes indicate that sorghum could serve as an important model species for C4-grasses. This review focuses on the potential advantages and disadvantages of these species as feedstocks and highlights the synergy provided by applying what is known from forage digestibility and wheat and sorghum starch properties to the biofuels sector.