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ARS Home » Midwest Area » Urbana, Illinois » Soybean/maize Germplasm, Pathology, and Genetics Research » Research » Publications at this Location » Publication #75684
Title: RESPONSE OF A HYPERNODULATING SOYBEAN MUTANT TO INCREASED PHOTOSYNTHATE SUPPLY

Author
item BACANAMWO, METHODE - U OF ILL, URBANA
item Harper, James

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Soybean nodules (specialized root structure) form when specific beneficial bacteria infect the soybean root for the purpose of converting atmospheric nitrogen to a form which is usable by the plant. The resulting association provides carbon compounds from the plant to support the bacteria, and the bacteria in turn provide nitrogen compounds for the plant, thus minimizing the need for nitrogen fertilizer application. This study showed that enhanced assimilation of carbon by the plant would stimulate plant growth and nodule function, but did not totally overcome the limited root growth pattern expressed by a soybean line specifically selected for enhanced number of nodules. Identification of limitations to enhanced symbiotic nitrogen fixation is important to scientists attempting to improve the productivity of soybean with minimal fertilizer inputs. Success in improving symbiotic nitrogen fixation will ultimately benefit farmers who are producing soybean, or may limit the amount of nitrogen fertilizer necessary for a corn crop grown in rotation with soybean.

Technical Abstract: Growth chamber studies were conducted to determine if increased photoassimilate supply, through light enhancement and CO2 enrichment, could reverse the deleterious plant growth and enhance nodule function traits of NOD1-3, a hypernodulating mutant of Williams. Both light enhancement and CO2 enrichment increased nodule number, nodule activity plant-1 (but not specific activity), and dry matter accumulation in all tissues in both genotypes. Total biomass and specific nitrogenase activity were always less in the mutant than in Williams 82, indicating that the inferiority of the mutant may not be reversed by enhanced photoassimilate supply. Under all growth conditions, the mutant allocated relatively more photosynthate to nodules and less photosynthate to roots, compared to the control. Despite this, the decreased growth of the mutant relative to the control was not solely attributable to excessive nodulation of the mutant, since decreased growth was observed even on uninoculated plants. It is suggested that light enhancement and CO2 enrichment may have stimulated nodulation through increased photosynthate supply, independent of the nodulation autoregulatory signal.