Analysis of functional differences among three Medicago sativa endophytic rhizobial strains

Three endophytic rhizobial strains (Sinirhizobium meliloti, LP3, WLP2, and WLG1) were inoculated onto Medicago sativa ‘WL168HQ' grown on sterilized sand in glass test tubes to analyze their symbiotic ability. The control was treated with cultural liquid without rhizobial strains. Strains were also studied to evaluate stress tolerance and growth promotion. Results showed that endophytic rhizobial strain WLP2 could tolerate all tested antibiotics (≥ 300 μg·mL-1) except for erythromycin and gentamycin. It could grow in a medium containing 6% NaCl and with pH 5~11, and could tolerate a temperature range of 8~40 ℃. This strain was able to dissolve organic phosphate (EYPC) and inorganic phosphate Ca3(PO4)2, and was capable of secreting indole acetic acid as well. The symbiotic effects of strain WLG1 were optimal. The nodule numbers, along with above-ground and below-ground dry weight of plants inoculated with WLG1, increased significantly (P<0.05) compared with the control, with increases of 208.16%, 72.35%, and 122.33%, respectively. Effective nodule weight, root length, and leaf number of plants inoculated with WLG1 increased by 6.68%, 9.57%, and 53.59% compared with the control, respectively. Altogether, endophytic rhizobial strain WLP2 presented high antibiotic, salt, pH, and temperature resistance and had a strong ability to promote plant growth, while strain WLG1 showed better inoculation effects on M. sativa ‘WL168HQ' and strong symbiotic nitrogen fixation.