Soybean yield, biological N2 fixation and seed composition responses to additional inoculation in the United States.

It is unclear if additional inoculation with Bradyrhizobia at varying soybean [Glycine max (L.) Merr.] growth stages can impact biological nitrogen fixation (BNF), increase yield and improve seed composition [protein, oil, and amino acid (AA) concentrations]. The objectives of this study were to evaluate the effect of different soybean inoculation strategies (seed coating and additional soil inoculation at V4 or R1) on: (i) seed yield, (ii) seed composition, and (iii) BNF traits [nodule number and relative abundance of ureides (RAU)]. Soybean field trials were conducted in 11 environments (four states of the US) to evaluate four treatments: (i) control without inoculation, (ii) seed inoculation, (iii) seed inoculation + soil inoculation at V4, and (iv) seed inoculation + soil inoculation at R1. Results demonstrated no effect of seed or additional soil inoculation at V4 or R1 on either soybean seed yield or composition. Also, inoculation strategies produced similar values to the non-inoculated control in terms of nodule number and RAU, a reflection of BNF. Therefore, we conclude that in soils with previous history of soybean and under non-severe stress conditions (e.g. high early-season temperature and/or saturated soils), there is no benefit to implementing additional inoculation on soybean yield and seed composition.

Proteomic Analysis of Soybean [Glycine max (L.) Merrill] Roots Inoculated with Bradyrhizobium japonicum Strain CPAC 15.

This research intended to analyze the expression pattern of proteins in roots of the Brazilian soybean cultivar Conquista when inoculated with Bradyrhizobium japonicum CPAC 15, a strain broadly used in commercial inoculants in Brazil. At ten days after bacterial inoculation, whole-cell proteins were extracted from roots and separated by 2-D gel electrophoresis. Comparative analysis revealed significant changes in the intensity of 37 spots due to the inoculation (17 up-regulated and 20 down-regulated proteins), identified by MALDI-TOF/TOF-TOF. Identified proteins were associated with COG functional categories of information storage and processing, cellular processes and signaling, metabolism, and also in the "poorly characterized" and "not in COG" categories. Among the up-regulated proteins, we identified sucrose synthase (nodulin-100), ß-tubulin, rubisco activase, glutathione-S-transferase, a putative heat-shock 70-kDa protein, pyridine nucleotide-disulphideoxidoreductase and a putative transposase. Proteomic analysis allowed for the identification of some putative symbiotic functions and confirmed the main biological processes triggered in the nitrogen-fixing symbiosis with soybean.