Development of Molecular Markers for Selection Against a Soybean Gene that Restricts Nodulation by the Highly Efficient Nitrogen-fixing Strain USDA 110

Crops of the legume family, such as alfalfa and soybeans, can make their own nitrogen fertilizer by forming symbioses with nitrogen]fixing soil bacteria known as rhizobia. This cross]kingdom collaboration is characterized by the formation of the root nodule, a specialized plant organ that provides an optimized environment for the bacteria to convert atmospheric nitrogen into ammonia. The legume.rhizobia association is highly specific, such that each rhizobial strain establishes an efficient symbiosis with only a limited set of plant genotypes, and vice versa. Even though many legumes can nodulate with indigenous soil bacteria, nitrogen fixation efficiency varies tremendously between different host]rhizobial combinations. Thus, there exists great potential to improve the symbiotic nitrogen fixation and consequently enhance the benefit of the legume]rhizobial symbiosis to sustainable agriculture. USDA 110 and its derivatives are commonly used commercial strains with high nitrogen fixation efficiency. However, certain soybean cultivars restrict nodulation by this strain; in this case, seed inoculant with the strains is not responsive. Thus, excluding the gene isoforms (alleles) that restrict nodulation by USDA 110 will be beneficial. We will employ genetic approaches to genetically localize the gene on the soybean chromosomes and to develop breeder]friendly molecular markers for efficient selection of favorable gene isoforms that allow for nodulation with these strains. The result from this project will facilitate the development of soybean varieties with improved nitrogen fixation efficiency, thus reducing the nitrogen input for soybean production.