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United States Department of Agriculture

Agricultural Research Service

Title: Genetic Mapping of the Soybean Gene Rj4, Conditioning Nodulation Restriction with Bradyrhizobium Elkanii, a Chlorosis-Inducing Microsymbiont, with Molecular Marker Loci

item Devine, Thomas
item Kuykendall, Larry
item Matthews, Benjamin
item Saunders, James
item Kenworthy, William - UNIV MD NTRL RES&LAND ARC

Submitted to: Symbiosis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 3, 1998
Publication Date: N/A

Interpretive Summary: An important agricultural advantage of soybean and other legume crop species is the ability of these plants to form a special relationship or symbiosis with certain bacteria called rhizobia. In this relationship the bacteria take nitrogen from the air and convert it into a form that the plant can use as a fertilizer to make protein. This enables farmers to grow such crops without the expense of purchasing fertilizer. Some bacteria form a symbiosis with soybean but do a poor job of fixing nitrogen with soybean. The Rj4 gene in the soybean plant prevents many of these poorly efficient bacteria from forming a symbiosis with soybean and allows the more efficient bacteria to do so. In this report, we describe the location of the Rj4 gene in the genetic map of soybean. This information will be helpful to soybean breeders in developing new soybean cultivars for farmers that will be more efficient in fixing nitrogen and more productive in producing valuable protein and oil for consumers. More productive cultivars will provide food to the American consumer at reasonable prices and maintain the competitiveness of American agriculture in world markets. 

Technical Abstract: The Rj4 allele protects soybean plants from nodulation by many strains of Bradyrhizobium elkanii, a rhizobitoxine chlorosis-inducing species with generally less efficient symbiosis with soybean. However, the frequency of the Rj4 phenotype shows progressive diminution with domestication in Asia and breeding for agronomic type in North America. This decrease in frequency might be due to linkage of the Rj4 gene with unknown genes selected against during domestication and breeding for agronomic type. For this reason it is of interest to determine the location of the Rj4 gene in the soybean genome. In this study, we tested the Rj4 gene for linkage with AFLP markers segregating in recombinant inbred lines of the cross of PI290136 X BARC -2 (Rj4). The Rj4 gene was mapped to a catena of AFLP markers. 

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