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Host Restriction of Nodulation by Bradyrhizobium japonicum Strain USDA 123 in Soybean¹

The displacement of indigenous Brudyrhizobium juponicum serogroup USDA 123 in soybean [Glycine mar (L.) Merr.] nodules in favor of a more effective inoculant strain(s) has been suggested as an approach to enhance soybean productivity in the midwestern USA. Our objective was to determine if the host plant could serve as a vehicle to restrict nodulation by an indigenous serogroup thereby allowing nodulation by a more effective rhizobial strain. A total of 1278 soybean plant introductions and cultivars were screened in the greenhouse with B. juponicum strain USDA 123. Thirteen genotypes demonstrated restricted nodulation with USDA 123 when compared to five standard cultivars. Two of these genotypes, PI 371607 and PI 377578, were planted along with the cultivar ‘Williams’ in a soil free of B. juponicum and inoculated with USDA 123 and either USDA 110,122, or 138. In each competition treatment, greater than 75% of the nodules of Williams were occupied by USDA 123 whereas, in all cases, less than 10% of the nodules of the PI genotypes contained USDA 123. The PI genotypes excluded strain USDA 123 in favor of the inoculant strain. In another experiment, the two PI genotypes and Williams were inoculated with either USDA 123 or 110. With USDA 123, nodulation and N accumulation was significantly less in the PI genotypes than in Williams. In contrast, with USDA 110, nodulation and N accumulation of the PI genotypes was similar to Williams. Thus, while the PI genotypes nodulated and fixed N2 poorly with USDA 123, nodulation and fixation with an efficient strain such as USDA 110 was normal. Our results suggest that the trait identified in the PI genotypes could positively impact soybean productivity by excluding all or part of the indigenous serogroup 123 population in favor of more effective strains of B. juponicum.

Key Words: Glycine max (L.) Merr. • Dinitrogen fixation • Rhizobial competition

² Research geneticist and soil microbiologist, USDA-ARS, Nitrogen Fixation and Soybean Genetics Lab., Range 1, GH-19, Beltsville Agric. Res. Ctr.-West, Beltsville, MD 20705.

Received for publication December 13, 1985.

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				S. Jitacksorn and M. J. Sadowsky Nodulation Gene Regulation and Quorum Sensing Control Density-Dependent Suppression and Restriction of Nodulation in the Bradyrhizobium japonicum-Soybean Symbiosis Appl. Envir. Microbiol., June 15, 2008; 74(12): 3749 - 3756. [Abstract] [Full Text] [PDF]