Collins Kimbeng, Niranjan Baisakh, Anna Hale, Kaitlin Barrios and Shyue Lu
Political, environmental and economic concerns have motivated nations to become increasingly interested in renewable sources of energy and bioproducts, such as those obtained from plant biomass. With a reputation as one of the most efficient crops in converting solar energy into chemical energy, sugarcane is being considered as a feedstock to fuel this fledgling bioenergy-bioproduct industry. LSU AgCenter researchers – partnering with researchers from private and public institutions including the U.S. Department of Agriculture-Agricultural Research Service in Houma, Louisiana – are in the forefront of developing genetically improved sugarcane varieties called energycane for this industry. The objective is to develop energycane varieties that can grow beyond the boundaries of the traditional sugarcane belt with optimum biomass yields and minimal inputs.
The idea of using sugarcane to generate energy is not new. Bagasse, the residue remaining after milling sugarcane to extract sucrose, is a principal source of energy used to power the milling process. Bagasse is burned to generate steam that powers the sugar mill, and in some instances, the excess electricity produced is sold to the electric grid. In Brazil, as a matter of public policy, sugarcane juice from the milling operation is used to produce ethanol, which is blended with gasoline and used as a transportation fuel. In the U.S., corn grain is used as the primary feedstock for ethanol production.
What is new, however, is the renewed objective of both the U.S. Department of Energy and USDA to replace a percentage of the current U.S. petroleum consumption with biofuels. This effort is expected to support the growth of agriculture in rural economies and foster new domestic industries such as biorefineries to produce a variety of fuels, chemicals and other bioproducts. Also new is the food-versus-fuel debate, which has brought into sharper focus the need to plant dedicated energy crops, such as energycane, in areas that will not compete with food crops.
The term energycane is used loosely to describe derivatives of sugarcane bred specifically as an energy crop. Recent energycane varieties have been developed by crossing cultivated sugarcane with its wild relative Saccharum spontaneum or the allied species Miscanthus. These crosses take advantage of traits such as biomass yield; tolerance to stresses from diseases, insect pests, drought and cold weather (Figure 2); and the ability to regrow after harvest without replanting. Selection in the resulting progeny focuses on maximizing biomass rather than sugar yield. Compared with sugarcane, energycane varieties are usually higher in biomass yield and fiber content and lower in sucrose content. The resulting feedstock used for bioprocessing is the lignocellulosic biomass.
AgCenter researchers, collaborating with scientists from the USDA-ARS in Houma, planted approximately 1,000 experimental varieties of energycane at the LSU AgCenter Macon Ridge Research Station in Winnsboro in 2012. These experimental varieties came from crosses specifically designed to maximize traits other than sucrose content, such as biomass yield, biomass quality and stress tolerance. Evaluating these experimental energycane varieties in Winnsboro, which is well outside of the traditional sugarcane belt, provides a challenging environment and the opportunity to select varieties that expand the geographical range of cultivation of energycane (Figure 1). Unlike traditional crops grown in this region, the energycane crop received no irrigation throughout its growth cycle. A sample of about 300 varieties that continued to show desirable characteristics was selected and replanted in 2013. Data collected so far, including the exposure of these experimental varieties in late 2013 to one of the coldest winters recorded in Louisiana, suggest a great potential for some of these varieties to be adapted for growth in colder climates outside of the traditional sugarcane- growing regions.
The ability of some energycane varieties to survive and thrive under very cold conditions in Louisiana presented AgCenter scientists with the opportunity to identify genes responsible for imparting cold tolerance. A number of cold-responsive genes have been isolated and characterized from an energycane variety. Genetic markers derived from these genes were used to distinguish among cold-sensitive commercial sugarcane hybrids, cold-tolerant Saccharum spontaneum and energycane clones. Further genetic mapping studies have led to the identification of several quantitative trait loci or genomic regions that contribute to different biomass and cold-tolerance traits. Ongoing efforts to identify genetic markers linked to these traits will facilitate the rapid screening and development of genetically improved energycane varieties with enhanced biomass yield and qualities that are suitable for cultivation in colder environments where sugarcane is not currently grown.
As in any chemical process, the quality of the raw material used for processing can affect the quality and quantity of the end product. Thus, feedstock quality of biomass destined for biorefineries will affect its value in much the same way as the quality of other agricultural products affects their use for food, animal feed, fiber and industrial products. AgCenter scientists are developing near infrared spectroscopy calibration curves to assist in the compositional analysis of energycane biomass. This provides a noninvasive tool to rapidly analyze biomass to assist the feedstock development program in selecting varieties and as a future means to assess feedstock market value.
Collins Kimbeng is a professor at the Sugar Research Station in St. Gabriel. Niranjan Baisakh is an associate professor, School of Plant, Environmental and Soil Sciences. Anna Hale is a research geneticist, Sugarcane Research Unit, USDA-ARS, Houma. Kaitlin Barrios is a research associate at the Sugar Research Station, and Shyue Lu is a research associate at the Audubon Sugar Institute, St. Gabriel.
(This article was published in the spring 2015 issue of Louisiana Agriculture Magazine.)