In the U.S., corn grain is a major source of animal feed, human food, and fuel ethanol for cars and trucks. The proportion of domestic corn grain used for producing ethanol increased from less than 10% in 2000 to about 30% in the last two years. Concerns have been raised on whether the ever-increasing demand for corn ethanol is contributing to higher food prices at the grocery store. To help address this food vs. fuel concern, the USDA and USDOE are promoting the development of plant feedstocks suitable for producing cellulosic ethanol.
In this scenario, plant materials rich in cellulose (such as leaves, stalks, or woodchips) are broken down into sugars that are fermented into ethanol. Corn grain would then be harvested for feed and food while a portion of the corn stover—the leaf, stalk, tassel, and cob residues that are normally left in the field—would be collected and used to produce fuel. Since the 1920s, hybrid corn varieties grown by U.S. producers have been bred for high grain yield and superior agronomic performance.
But these varieties have not been bred for qualities that would make their stover suitable for producing cellulosic ethanol. Could tomorrow’s corn have high grain yields and superior stover quality for cellulosic ethanol? Or would breeding for cellulosic ethanol adversely affect grain yield and agronomic performance? Genetic studies conducted by professor Rex Bernardo of the University of Minnesota, Dr. Hans-Joachim G. Jung of the USDA-ARS, and graduate students Magan Lewis and Robenzon Lorenzana at the University of Minnesota have indicated that breeding for such dual-purpose corn hybrids is feasible.
These studies were reported in the March–April 2010 issue of Crop Science. The Minnesota researchers found either neutral or favorable relationships among grain yield, stalk lodging, and stover quality traits considered most important for producing cellulosic ethanol. Even though current corn lines have not been bred for cellulosic ethanol, they exhibited a significant amount of genetic variation for the stover-quality traits.
DNA fingerprints indicated the lack of “silver-bullet” genes for cellulosic ethanol: instead, stover quality for cellulosic ethanol is controlled by many genes that need to be accumu-lated in a corn hybrid by selective breeding.
Bernardo is now investigating the use of DNA fingerprints and year-round breeding nurseries in a fast-track approach to breed for dual-purpose corn. He and Jung remain cautious, however, on the prospects of large-scale production of corn for grain and cellulosic ethanol on U.S. farms.
“What we’re studying is the first small piece of the puzzle,” Bernardo notes, “and big pieces of the cellulosic-ethanol puzzle remain to be solved.”
In particular, how much of the corn stover can be removed from the field without adversely affecting soil quality? Can corn stover be efficiently transported and stored? And will the demand for cellulosic ethanol be large enough to entice seed companies, who develop virtually 100% of the corn hybrids grown by farmers, to begin developing dual-purpose corn hybrids?
While these questions remain to be answered, we at least now know that a dual-purpose corn plant for stomachs and stills can be developed.
Photo: University of Minnesota staff scientist Eric Ristau samples corn stover for cellulosic ethanol. Photo submitted to CSA News by the authors.
Adapted from Lewis, M.F., R.E. Lorenzana, H.-J.G. Jung, and R. Bernardo. 2010. Potential for simultaneous improvement of corn grain yield and stover quality for cellulosic ethanol. Crop Sci. 50:516–523. View the full article online at http://crop.scijournals.org/content/vol50/issue2
Lorenzana, R.E., M.F. Lewis, H.-J.G. Jung, and R. Bernardo. 2010. Quantitative trait loci and trait correlations for maize stover cell wall composition and glucose release for cellulosic ethanol. Crop Sci. 50:541–555. View the full article online at http://crop.scijournals.org/content/vol50/issue2