Symbiotic Characteristics of a New Indigenous Sinorhizobium Strain 98002 from Medicago polymorpha in Poyang Lake Wetland

Medicago polymorpha serves as an important green manure, forage, and edible wild vegetable. Symbiotic nitrogen fixation represents its primary nitrogen source; nevertheless, rhizobial strains that establish symbiotic interactions with this plant have rarely been isolated, particularly from distinctive wetland habitats. In this work, sinorhizobial strain 98002 was isolated from root nodules of wild M. polymorpha collected at Poyang Lake wetland. Scanning electron microscopy (SEM) was applied to observe its cellular morphological features, and molecular identification combining 16S rRNA sequencing and six concatenated housekeeping gene multilocus sequence analysis (MLSA) confirmed the isolate as Sinorhizobium medicae. Antibiotic susceptibility tests demonstrated that strain 98002 was fully sensitive to seven common antibiotics. Host inoculation assays further verified that this indigenous strain could develop pink nodules on M. polymorpha roots and remarkably improve host biomass accumulation under nitrogen-deficient conditions. This indigenous rhizobial resource serves as promising germplasm for sustainable M. polymorpha cultivation in the Poyang Lake basin.