Symbiotic performance of indigenous soybean bradyrhizobia from the Philippines with soybean (Glycine max [L.] Merill) cultivars harboring different Rj genotypes

This report aimed to evaluate the ability of the dominant indigenous strains of bradyrhizobia obtained from different locations in the Philippines in terms of their symbiosis, N-fixation and nodulation with various soybean cultivars harboring different Rj genotypes. This was done to select the most efficient and effective strain that can be used as an inoculant under the Philippines' local condition. Two soybean cultivars from the Philippines and three cultivars from Japan and Brazil were used and inoculated with 12 indigenous strains and the reference strain Bradyrhizobium diazoefficiens USDA110. Culture pots were grown inside a growth chamber for four weeks with 33 degrees C for 16 h as daytime and 28 degrees C for 8 h as night time. All the strains formed nodules on all soybean cultivars, except for B. elkanii BO-4, which only formed nodules on Philippines' cultivars. Among the indigenous strains, B. elkanii IS-2 is significantly the most efficient and effective N-fixer than the other strains for the Philippines' cultivars. In contrast, B. diazoefficiens SK-5 was found to be the most efficient and effective N-fixer for cultivars from Japan and Brazil. Additionally, a positive correlation was observed between the symbiotic efficiency and the nitrogenase activity indicating an efficient N-fixation by the indigenous strains. Thus, we were able to identify the most promising indigenous bradyrhizobia that could be used as an inoculant to increase the soybean yield in the Philippines and provided insights on soybean inoculation.

Automated summary

The study evaluated the performance of indigenous Bradyrhizobia strains in soybean cultivation, with B. elkanii IS-2 identified as the most efficient for Philippines cultivars and B. diazoefficiens SK-5 for Japanese and Brazilian cultivars. Positive correlation was found between symbiotic efficiency and nitrogenase activity, indicating efficient N-fixation by indigenous strains. This research provides insights for soybean inoculation in the Philippines.