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Title: IMPROVING TOLERANCE OF N2 FIXATION IN SOYBEAN TO DRYING SOIL

Author
item Sinclair, Thomas
item Purcell, Larry
item Vadez, Vincent
item Serraj, Rachid

Submitted to: Agronomie Agriculture Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: Symbiotic nitrogen fixation in soybean offers a natural advantage in the production of this crop because it is not necessary to apply nitrogen fertilizer. It has been discovered, however, that nitrogen fixation in soybean is very sensitive to soil drying and that rates begin to decline with only modest soil drying. This research, led by an ARS-USDA scientist located at the Center for Medical, Agricultural and Veterinary Entomology, Gainesville, FL, explored possibilities for developing soybean varieties that have nitrogen fixation less sensitive to soil drying. A multi-stage scheme for screening for tolerant lines of soybean was developed based on results from earlier studies investigating the critical physiological traits associated with the drought response. This screening scheme was applied to over 3000 soybean lines and eight lines were identified as having exceptional tolerance. Research is now underway to understand the basis of the tolerance found in these eight lines and to use these lines in breeding efforts to develop superior soybean varieties.

Technical Abstract: Symbiotic N2 fixation in soybean is very sensitive to soil drying with decreases in activity usually occurring well in advance of declines in other physiological processes. Loss in N2 fixation activity results in losses of nitrogen accumulation and yield. This study was undertaken as a large-scale, systematic effort to identify soybean lines with superior N2 fixation tolerance for use in soybean breeding programs. The approach was unique in that physiological considerations were used to develop a three-stage screening approach. The first stage was used to identify candidate lines for intensive screening based on petiole ureide levels. High petiole ureide levels had been shown to be associated with N2 fixation sensitivity to drought. The second stage screen was a direct measure of the selected lines for N accumulation under field, drought conditions. The third stage focused directly on N2 fixation activity with a greenhouse screen of acetylene reduction activity under drying soil conditions. From an original population of over 3000 plant introduction lines, eight lines were identified as having N2 fixation tolerance to soil drying.