Genetic improvement of symbiotic nitrogen fixation in soybeans

a. Abstract – Technical The overall goal of this project is to investigate the soybean Rj4 gene that controls strain-specific nodule development in soybeans. Rj4 restricts the host plant from nodulation with many strains of Bradyrhizobium elkanii. B. elkanii strains are frequently present in soils of the southeastern US and readily nodulate most soybean cultivars. However, B. elkanii strains are considered as poor symbiotic partners of soybeans, and many of the strains also produce rhizobitoxine, a compound that induces chlorosis in the host plant. Thus, cultivars containing an Rj4 allele are favorable in soils where B. elkanii strains are common. The Rj4 allele occurs with high frequency in Glycine soja, the wild progenitor of soybean, and in soybean cultivars from Southeast Asia. In contrast, the Rj4 genotypes are less frequent in cultivars from North America. Genetic localization of Rj4 gene will allow developing molecular markers for selection of soybean genotypes that contain the Rj4 allele. b. Abstract – Non-technical The overall goal of this project is to investigate the soybean Rj4 gene that controls strain-specific nodule development in soybeans. Rj4 restricts the host plant from nodulation with many strains of Bradyrhizobium elkanii. B. elkanii strains are frequently present in soils of the southeastern US and readily nodulate most soybean cultivars. However, B. elkanii strains are considered as poor symbiotic partners of soybeans, and many of the strains also produce rhizobitoxine, a compound that induces chlorosis in the host plant. Thus, cultivars containing an Rj4 allele are favorable in soils where B. elkanii strains are common. The Rj4 allele occurs with high frequency in Glycine soja, the wild progenitor of soybean, and in soybean cultivars from Southeast Asia. In contrast, the Rj4 genotypes are less frequent in cultivars from North America. Genetic localization of Rj4 gene will allow developing molecular markers for selection of soybean genotypes that contain the Rj4 allele.