Nitrogen-Boosting Potential Found in Soybeans

A newly identified gene in soybeans could help farmers boost crop yields and cut fertilizer costs.

Soybean plants' roots typically form nodules that become microscopic homes for a special type of soil-dwelling bacteria called rhizobia. Inside the nodules, these bacteria transform nitrogen from the atmosphere into ammonia, a form of nitrogen that plants can use for growth. Ordinary soybeans can add about 40 pounds of usable nitrogen to an acre of soil.

Agricultural Research Service scientists at the Plant Physiology and Genetics Research Unit at Urbana, Ill., have now identified the gene that regulates a process called "hypernodulation" in soybean plants. A hypernodulating soybean plant produces hundreds of additional root nodules, which opens the door to significantly greater nitrogen transformation by rhizobia.

A typical commercial soybean cultivar generates up to 200 nodules on its root system during the first month of growth, but a hypernodulated mutant soybean can generate as many as 1,000 nodules during that time.

Typical soybean cultivars genetically "turn off" the nodule-making machinery when signaled by a chemical produced in the shoot of the plant. Scientists are now working to discover the chemical makeup of that signal and how it tells the soybean plant when to "turn on" and "turn off" its nodule-forming machinery.

If scientists can learn more about this chemical and how it interacts with the hypernodulating gene, they may be able to regulate the trait in commercial soybean lines, potentially reducing nitrogen fertilizer applications.

A complete story on this research can be found in the January issue of Agricultural Research, the monthly magazine of the Agricultural Research Service. The article is also on the World Wide Web at:

http://www.ars.usda.gov/is/AR/archive/jan98/gene0198.htm

Scientific contact: James E. Harper, Plant Physiology and Genetics Research Unit, Urbana, Ill., phone (217) 244-6670, fax (217) 333-6089, j-harper@uiuc.edu.