Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 28, 2013
Publication Date: October 9, 2013
Citation: Hwang, S., Ray, J.D., Cregan, P.B., King, C., Davies, M., Purcell, L. 2013. Genetics and mapping of quantitative traits for nodule number, weight, and size in soybean (Glycine max L. [Merr.]). Euphytica. 195:419-434. Interpretive Summary: Nitrogen fixation is the process by which certain types of plants obtain nitrogen from the atmosphere in a symbiotic relationship with bacteria. This process occurs in specialized plant structures called nodules that occur on the roots of soybean plants. Differences in the number and size of nodules may influence the rate and amount of nitrogen produced. These differences were evaluated in a genetic population and then molecular markers used to identify the possible locations of genes involved in controlling the differences. Over three years of evaluation of the population and using multiple methodologies, up to five potential locations of genes were identified. Knowledge of these locations may be useful in selecting soybean lines with more efficient or productive nitrogen fixation.
Technical Abstract: Legume studies, including soybean, have reported that nodule traits, especially nodule biomass, are associated with N2 fixation ability. Two genotypes, differing in nodule number and individual nodule weight, KS4895 and Jackson, were mated and used to create 97 F3- and F5-derived RILs. The population was mapped with 664 informative markers to a density of less than 20 cM. Nodule traits were evaluated in 3-year field trials under irrigated conditions. Broad-sense heritability for nodule number (no. plant-1), individual nodule dry weight (mg nodule-1), individual nodule size (mm nodule-1), and total nodule dry weight (g plant-1) was 0.41, 0.42, 0.45, and 0.27, respectively. Nodule number was negatively correlated with individual nodule weight and size. Nodule number, individual nodule weight, and size are major components which likely contributed to increased total nodule weight. Composite interval mapping (CIM) identified eight QTLs for nodule number with R2 value ranging from 0.14 to 0.22. Multiple interval mapping (MIM) identified two QTLs for nodule number, one of which was located close to the QTL identified with CIM. Six QTLs for individual nodule weight were detected with CIM, and one QTL was identified with MIM. Additive effects ranged from 0.12 to 0.32 mg nodule-1. For nodule size, CIM identified seven QTLs with R2 value ranging from 0.14 to 0.27. Five QTLs for total nodule weight were detected with CIM, one of which was located close to a QTL identified with MIM. Considering QTL x Year interactions based on a CIM model, all QTLs were stable over years. Identified QTLs were positioned close to traits which have been reported to be involved in seed characteristics (oil, protein, and weight), phenology, yield and reactions to biotic-stresses. These results document the first QTL information on nodule traits in soybean from field experiments utilizing a dense, complete linkage map.