Evaluation of effective Myanmar Bradyrhizobium strains isolated from Myanmar soybean and effects of coinoculation with Streptomyces griseoflavus P4 for nitrogen fixation

Abstract In order to substitute the use of chemical fertilizers in legume production, there is a need for the production of rhizobial inoculants which are capable of being used as biofertilizers. To achieve this, an effective symbiotic nitrogen (N) fixation between legumes and root nodule bacteria will be essential. Evaluation of effective Myanmar Bradyrhizobium (Jordan 1982) strains isolated from Myanmar soybean (Glycine max L. Merr.) and effects of coinoculation with Streptomyces griseoflavus Krainsky 1914 P4 for N fixation were studied in pot experiments using sterilized vermiculite and Hoagland solution in the Phytotron (25°C and 70% relative humidity) with completely randomized design and three replicates. N fixation ability of soybean was evaluated by acetylene reduction activity (ARA) by gas chromatography. It was found that MAS23 showed a relatively high degree of stability and a high level of ARA per plant on both Yezin-3 and Yezin-6 soybean varieties. In the symbiotic relationship between Bradyrhizobium strains and P4 experiments, the treatments consisted of six Bradyrhizobium strains (MAS23, MAS33, MAS34, MAS43, MAS48 and USDA110) and Streptomyces griseoflavus P4 were evaluated with four Myanmar soybean varieties (Yezin-3, Yezin-6, Hinthada and Shan Sein). In the Yezin-3 soybean variety, the best treatment for ARA per plant was found in the dual inoculation of P4 and MAS34. In the Yezin-6 soybean variety, the highest nodule dry weight was found in dual inoculation of P4 with MAS34 but the highest ARA per plant was observed in the dual inoculation of P4 and MAS23. On the other hand, single inoculation of MAS43 and coinoculation of P4 with MAS48 were significantly higher in N fixation of Hinthada, and coinoculation of P4 with MAS33 was significant improvement of ARA per plant (P < 0.05) in Shan Sein soybean.