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Title: VARIATION AMONG SOYBEAN CULTIVARS IN DINITROGEN FIXATION RESPONSE TO DROUGHT.

Author
item SERRAJ, R. - MARRAKECH, MOROCCO
item Sinclair, Thomas

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Soybean is important in crop rotation schemes employed by growers because it does not require the application to the soil of nitrogen fertilizer. Soybean plants obtain their nitrogen from the atmosphere in a process called dinitrogen fixation. It has recently been discovered by scientists at the Agricultural Research Service in Gainesville, FL, that the dinitrogen fixation process is particularly sensitive to soil drying. Early in the soil drying cycle the dinitrogen fixation process begins to decrease. This study was undertaken to examine the possibility that there is genetic variation for this trait among soybean cultivars. Field and greenhouse tests clearly demonstrated important differences in the sensitivity of dinitrogen fixation sensitivity to drought among cultivars. A previously identified cultivar 'Jackson' again proved to be superior to other cultivars in its drought tolerance.

Technical Abstract: Dinitrogen fixation in soybean [Glycine max (L.) Merr.] is especially sensitive to drought. Two field experiments were conducted to examine the genetic variation in the sensitivity of soybean cultivars for biomass and nitrogen accumulation rates in response to soil drying. Substantial variation among soybean lines was found, and the drought tolerance trait has been confirmed in Jackson as well as in a few other lines. Interestingly, the differences between cultivars in the response of nitrogen accumulation to drought stress were associated with differences in petiole ureides concentration (PUC). An experiment was conducted in the greenhouse with eight soybean cultivars grown in pots and exposed to drought by soil dehydration over a two-week period. In contrast to the field experiments, no consistent relationship was found among the eight genotypes between PUC changes and the response of N2 fixation to drought. There was, however, a significant negative correlation between the drought tolerance of N2 fixation and ureide concentration in the xylem sap. Therefore, these data supported the hypothesis of the involvement of ureide metabolism in drought stress effects on N2 fixation.