Unlocking the Potential of Inoculation with Bradyrhizobium for Enhanced Growth and Symbiotic Responses in Soybean Varieties under Controlled Conditions

Soybean is a crucial crop for sustainable agriculture development as it forms symbiotic relationships with rhizobia species. The effectiveness of inoculants in symbiosis, however, relies on the compatibility of the strain with a specific legume crop variety. This study assessed the symbiotic efficiency of eight Bradyrhizobium strains (SB-36, SB-37, SD-47, SD-50, SD-51, SD-53, SB-113, and SB-120) with five soybean varieties (Gishama, Awassa-95, Boshe, Hawassa-04, and Jalale) using sand culture. The experiment was arranged in a factorial, completely randomized design with three replicates. Data were collected on plant growth, and symbiotic effectiveness indices and subjected to statistical analysis using R software v4.3.1. The results revealed marked differences (p < 0.001) between the varieties, rhizobial strains, and their combined effects on all traits examined. The Jalale variety inoculated with Bradyrhizobium strains SB-113 and SD-53 produced the highest nodules per plant. When inoculated with SD-53, Awassa-95 demonstrated the highest relative symbiotic effectiveness [129.68%], closely followed by the Boshe variety [128.44%] when inoculated with the same strain. All strains exhibited high relative symbiotic effectiveness (>80%) with Awassa-95 and Boshe varieties. The highest absolute symbiotic effectiveness was observed in the Gishama variety inoculated with the SD-53 strain followed by Boshe and Awassa-95 varieties inoculated with this same strain. Notably, strain SD-53 demonstrated remarkable efficiency with the varieties Gishama, Boshe, and Awassa-95 based on both relative and absolute symbiotic effectiveness indices. Varieties inoculated with the SD-53 strain produced deeper green leaves. This study revealed the importance of Bradyrhizobium inoculation to improve soybean performance, for which the SD-53 strain performed best among the strains considered in the current experiment. Therefore, it is plausible to recommend inoculating soybeans with Bradyrhizobium strain SD-53 with prior field evaluation.