Development of Soybean Genotypes with Enhanced Capacity for Nitrogen Fixation
by Stella K. Kantartzi, Southern Illinois University-Carbondale
Soybean roots with nodules
In soybean, the symbiotic nitrogen (N)-fixing bacteria provide the needed N to the plant; however, the modern cultivars rely on N fertilizers to achieve their full yield potential. Therefore, the improvement of di-nitrogen fixation capacity is considered essential in soybean breeding and might be achieved through the evaluation of traits related to biological nitrogen fixation (BNF).
Biological nitrogen fixation in soybean reaches the highest rate in the R2–R4 stage and then, gradually decreases in the late reproductive stages. Soybean plants that fix significant amounts of N in the late reproductive stages also have a high photosynthetic rate that allow them to supply the Rhizobium with carbohydrates. The amount of N assimilated by the plants through BNF during the pod-filling stage is positively correlated to seed weight, and consequently, seed yield.
In the recently completed study funded by the North Central Soybean Research Program, we screened a core collection of soybean genotypes with different genetic backgrounds and detected those with a significantly high capacity for BNF. We also detected traits that are directly and indirectly associated with BNF such as SPAD readings (for chlorophyll), leaf %N, shoot dry mass, total seed weight, mean weight per seed, total seed number, days to maturity, pod %N, nodule number, and nodule dry weight.
These traits were used as selection criteria to develop two genetic populations with distinct traits for BFN. Both populations will be phenotyped under greenhouse conditions and genotyped with SNP markers (short DNA sequences) to identify genomic regions associated with improved BNF. Markers that are closely associated to BNF will enhance our ability to select and develop highly productive soybean lines that do not rely on N fertilizers to reach their maximum yield potential.