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Bacterial strains formerly isolated from the root nodules of indigenous and exotic forage legumes and preserved at the South African Rhizobium Culture Collection (SARCC) were tested for nodulation of their original host. The nodulation authentication trial was conducted following the Koch’s postulate experiment under glasshouse condition and revealed that all bacterial strains are root nodule micro-symbionts of the forage legumes from which they were initially isolated. Nodulation and improved growth of the legumes was achieved by the tested strains with statistically significant (p = 0.05) increase in plant biomass and nodule number in comparison with the un-inoculated controls. To elucidate their identity and phylogenetic relatedness, the effective strains were selected and characterized by means of the 16S ribosomal RNA sequence analysis. The analysis confirmed that the isolates nodulating Macrotyloma axillare, Desmodium uncinatum, Indigofera spicata var. spicata and Stylosanthus gracillis predominantly belong to the genus Bradyrhizobium. Vigna unguiculata and Vigna sp. were nodulated by strains belonging to members of the genus Bradyrhizobium, Sinorhizobium and Rhizobium. The results obtained in this study provide baseline information in the investigation of the legume-rhizobium interaction on South African soils, and are also of paramount importance in the selection and development of commercial rhizobium inoculants for sustainable production of forage and other essential legumes. |
