Author
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Harper, James |
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Submitted to: Nitrogen Fixation International Congress
Publication Type: Abstract Only Publication Acceptance Date: 8/4/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: Genetic progress in understanding symbiotic dinitrogen fixation has involved both natural selection and mutagenesis. Both nonnodulating and hypernodulating lines have been identified and genetically characterized. Nonnodulation in soybean was initially identified as a spontaneous mutation and the gene symbol rj1 was assigned. Additional nonnodulation mutants of soybean were identified and genetic evaluation revealed three recessive genes (rj1, rj5, and rj6) involved in control. The hypernodulating mutants are also controlled by single recessive Mendelian genes, and to date only one identified locus (rj7) has been approved by the Soybean Genetics Committee. Evaluation of the hypernodulation mutants in the field show partial tolerance of the nodule development process to soil nitrogen, but dinitrogen fixation values on an area basis over the growing season are similar to normally nodulated cultivars. Yields of the mutant lines were typically 20 to 30% less than that of check cultivars, likely due to restricted root growth that seems inherent in all the hypernodulating lines. Advanced generation backcross lines were obtained which retain some degree of enhanced early nodulation, and have similar agronomic performance to that of normally nodulated check cultivars. Although efforts to exploit hypernodulation to enhance yield have not been very successful, it is reported that dry matter production of oats or barley was significantly increased when following hypernodulated soybean, compared with commercial cultivars. Should this result prove to be consistent, and at least similar yield levels are attainable between hypernodulating and normally nodulating cultivars, there is reason to consider releasing advanced generation hypernodulating lines. |
