DESPITE the fact that sorghum — an ancient cereal grain originating from Africa — underwent adaptation to be grown in temperate climates decades ago, a University of Illinois research team led by Patrick Brown, an assistant professor in plant breeding and genetics, has completed the first comprehensive genomic analysis of the molecular changes behind that adaptation.
In 2012, U.S. farmers grew 246.9 million bu. of sorghum in 14 states. Sorghum — a grain, forage or sugar crop — is a high-energy, drought-tolerant crop used for livestock feed and ethanol production and as a wheat substitute in gluten-free foods.
Past breeding efforts were focused on selecting and crossing exotic lines with temperate-adapted lines to create plants that were photoperiod insensitive for early maturity and short enough to be machine harvested.
Although sorghum has the ability to produce high yields on marginal lands, it has some limiting factors, such as poor weed control. In fact, sorghum is not a contender for glyphosate tolerance traits because there is a potential for the resistance to transfer to closely related problematic weeds.
Brown said having a complete characterization of the genetic locations (loci) that affect specific traits will speed up the adaptation of sorghum and other related grasses to new production systems for both food and fuel.
The researchers used a new technique called genotyping-by-sequencing (GBS) to map genetic differences in 1,160 sorghum lines. Brown said GBS is a new technology that was developed in the last two years.
"Using GBS, we're now able to cover the whole genome with some gaps in individual lines," he said.
"Surprisingly, no one had ever really genotyped these lines to figure out what had happened when they were adapted," Brown added. "Now that genotyping is cheap, you can get a lot of data for a modest investment."
While much improvement has been made for grain sorghum, little development has occurred for the sweet or bioenergy types.
"Part of the reason for caring about all of that now is that, up to this point, sorghum has mostly been grown for grain," Brown said. "It's pretty short stuff, doesn't blow over on the windy High Plains and is really hardy, but now, there is a lot of interest in using sorghum for other things, such as growing sweet sorghum in areas where they grow sugarcane and growing biomass sorghum for bioenergy through combustion or cellulosic technology."
Processing sweet sorghum is similar to sugarcane in producing ethanol. For growers in the southern U.S., it could mean raising multiple crops. Florida farmers, for instance, report harvesting 2.5-3.0 crops of sorghum in a single year.
Harvested at the time of frost, bioenergy sorghum has a high moisture content and lots of biomass, which is a stumbling block for cellulosic ethanol. Nevertheless, since the sugary juice is squeezed from sweet sorghum similarly to sugarcane, it is closer to being a viable biofuel feedstock.
"The bigger problem with biomass sorghum right now is the moisture content of the biomass," Brown explained. "Unlike miscanthus or switchgrass, where you can go in and harvest in February, when it's pretty much bone dry and all the nitrogen has already been moved back down underground, sorghum doesn't work that way."
Getting a complete map of the plant's genes will allow researchers to bring desirable traits from grain sorghum, like seed quality or early-season vigor, to make improvements in sweet, forage or biomass sorghum.
"We'll be able to start moving forward. We'll basically be able to breed all these sorghum types more easily and use the genes that we bred for in grain sorghum over the last hundred years and move them into sweet sorghum and biomass sorghum. We think that finding those genes is going to be critical," Brown concluded.
Brown is working on the project through the Energy Biosciences Institute, a collaborative effort with partners from the University of Illinois, University of California-Berkeley and Lawrence Berkeley National Laboratory.
"Retrospective Genomic Analysis of Sorghum Adaptation to Temperate-Zone Grain Production" was published this year in Genome Biology.
Value-added opportunities for sorghum grain are on the horizon thanks to genetic studies and improvements, Brown added.
Until recently, the phenolic acid and tannins present in sorghum caused its flour to have a bitter flavor. Newly developed food-grade sorghum hybrids do not contain these components and currently are being used in snack foods to replace wheat flour.
Sorghum also produces 10 times more antioxidants than blueberries, which could boost its global demand, but the yields of food-grade sorghum hybrids are significantly lower.
Genetic mapping will accelerate the process of utilizing desirable genetics for future global uses of sorghum. This versatile crop is considered a feasible substitute for corn or wheat in biofuels, food and livestock feed worldwide.