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SORGHUM GENE MAPPING DEVELOPS STAY-GREEN LINE

LUBBOCK -- Plant science researchers at Texas Tech University are narrowing the gap between sorghum that dies prematurely due to heat and moisture stress and lines of the crop that seem to display "stay-green" characteristics allowing plants to mature normally in high-heat areas, and creating higher yield for producers.

A team of international researchers, under the direction of Henry T. Nguyen, Ph.D., Texas Tech Horn professor of plant genetics in the department of plant and soil science, are using DNA markers - or gene mapping - to breed new lines of sorghum that contain many more drought resistance and moisture stress tolerance properties. This project is the first in the world to apply molecular marker technology to breeding for drought tolerance in sorghum.

The problem, said Nguyen, is that most commercially produced sorghum hybrids in the United States possess little post-flowering drought tolerance. That is, if there is drought stress after flowering and before the seeds reach maturity, the plant ceases the photosynthesis necessary to fill out the seed with the proteins and carbohydrates important for cattle and human consumption.

"Stay-green genes delay the premature death of leaves and plants, help the normal grain filling and reduce the incidence of lodging, or plants just falling dead to the ground," said Nguyen. "Some lines of sorghum remain green with good stand, and it is the genes from those particular lines we want to identify and manipulate."

Nguyen explained that the gene-mapping procedure is particularly important to drought tolerance research because of timing. Typically, he said, a researcher using conventional breeding methods must wait through each growing season before the visual evidence is present whether a line will have the obvious stay-green characteristics. Since conventional researchers can only do their plant selection once a year, the process takes a very long time to get to a generation in which the genes are particularly strong.

"By using DNA markers to follow the genes, we can breed the plants approximately three times a year instead of only once during the regular growing season. The process becomes more efficient, since we don't have to wait for the plant to express (show visual characteristics)," Nguyen said.

"We have pinpointed four different chromosomal regions in the sorghum where these stay-green genes exist. Any time we can conduct genome mapping like this, we can pinpoint certain DNA markers as landmarks on a particular chromosome. The next step will be to continue selection and breeding, following the genes at the DNA level," Nguyen said.

The ultimate goal, according to Nguyen, is to eventually identify the genes, or DNA sequences, and tell precisely what genetic characteristics they carry, what it does and why, at the cellular biochemical level. He also said his research is a few years away from commercially producing the heartier stay-green lines.

Sorghum is an important part of the Texas cropping system. "First of all, sorghum can grow here. It does well in a semi-arid climate. Secondly, producers need options for crop rotation to ensure a sustainable system of agriculture," Nguyen explained. "Sorghum can be rotated with cotton, just like wheat and corn. Thirdly, with the prevalence of the cattle feed industry in this part of the state, sorghum could certainly be used much more in this area, creating a larger demand for the grain."

According to Nguyen, the state produces about 4 million acres of sorghum each year, mostly in the Texas High Plains and Coastal Bend area around Corpus Christi. "Texas is either number one or number two in the United States, depending on the year, behind Kansas, in sorghum production. In the U. S., the crop is used mostly as an animal feed," Nguyen said.

Nguyen explained that sorghum also is a global crop, much like corn and wheat, and is used widely as an additive in human consumables. "India grows a lot of sorghum, as does Africa, Mexico, Central America, Brazil and China."

"The applications to the producer will be, of course, improved stand and higher yield under stress conditions, which results in fewer losses and lower production costs," Nguyen said.

The research is funded through a grant from the United States Department of Agriculture National Research Initiative Plant Genome project, the state's Tex GRAINS program and four major seed companies. Nguyen's collaborators include Darrell Rosenow of the Texas Agricultural Experiment Station as well as Hirut Kebede, an Ethiopian scientist supported by the Rockefeller Foundation program on advance training and fellowship for developing countries.

Nguyen believes that researchers in Lubbock and at Texas Tech can be considered the pioneers in developing sorghum into a major commodity for the area, the state and the country. He says there have been scientists working in this area since the 1950s, mostly at the Experiment Station in the early years, to research this crop.

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Contact:
Henry T. Nguyen, Ph.D., Horn professor of plant genetics, department of plant and soil science, (806) 742-1622, or email to [email protected].