Selection and evaluation of Bradyrhizobium inoculum for peanut, Arachis hypogea production in the Lao People’s Democratic Republic

The interaction between leguminous plants and Bradyrhizobium is limited, known as host specificity. Therefore, the selection of an appropriate Bradyrhizobia for use as biofertilizer inoculum for legumes is necessary. The Arachis hypogea L. is the most popular legume produced in the Lao People's Democratic Republic (PDR). Therefore, this research aimed to obtain the appropriate Bradyrhizobia that provides high efficiency in A. hypogea production in the Lao PDR. The 14 isolates were obtained from root nodules of A. hypogea L. trapped with Lao PDR soil samples. Three were the top isolates PMVTL-01, SMVTL-02, and BLXBL-03 showing high efficiency for peanut growth promotion. Strains PMVTL-01 and SMVTL-02 were closely related to the Bradyrhizobium geno sp. SA-3 Rp7b and B. zhanjiangense, respectively, whilst strain BLXBL-03 was closely related to Bradyrhizobium sp. CCBAU51745 and B. manausense BR3351. The competitiveness of these strains with Bradyrhizobium sp. SUTN9-2::GFP was analyzed, and only Bradyrhizobium sp. SMVTL-02 performed a number of occupied nodules higher than SUTN9-2::GFP. In addition, the competitiveness of the selected strain Bradyrhizobium sp. SMVTL-02 in a soil sample from the Lao PDR in the pot level was employed by tagging the SMVTL-02 with the DsRed gene. The results demonstrated that the DsRed-expressing tagged strain showed higher nodule occupancy than indigenous strains. Moreover, the results of the acetylene reduction assay (ARA), nodule number, nodule dry weight, and total plant dry weight from the pot experiment that inoculated with the SMVTL-02::DsRed were presented as having high potential to promote peanut growth as compared to non-inoculation. Thus, Bradyrhizobium sp. SMVTL-02 could be considered a potential biofertilizer inoculum for A. hypogea production in the Lao PDR.