Antagonistic effects of endophytic bacterial strains isolated from alfalfa and identification of strains with excellent antagonistic activities

In this study, endophytic bacteria were isolated from the stems and roots of alfalfa (Medicago sativa) and the antagonistic effects of these bacteria against the fungal pathogens Fusarium chlamydosporum, F. oxysporum, F. solani, F. oxysporum, F. avenaceum, and F. acuminatum were evaluated using the flat confrontation method. Selection of endophytic bacteria with excellent antagonistic activities was based on morphology and sequence analyses of 16S rDNA, and for the identified strains, we established biological functions and quantitively determined the effects on the ability to fix nitrogen, solubilize phosphorus (inorganic phosphorus), and secrete auxins. We succeeded in isolating 80 strains of endophytic bacteria from the stems and roots of alfalfa, among which, 39 strains showed more than 50% inhibition against F. chlamydosporum. Moreover, nine of these strains, namely, MS-43 (63.96%), MS-40 (63.75%), MS-46 (63.54%), MS-2 (63.13%), MS-31 (62.29%), MS-52 (62.08%), MS-80 (61.88%), MS-55 (61.46%), and MS-33 (61.25%), showed more than 61% inhibitory activity. In addition, the inhibitory activities of strains MS-40, MS-43, MS-46, and MS-50 against the other six assessed strains of Fusarium spp. were all higher than 60%. The average inhibition rate of MS-43 was 66.11% and this strain was also characterized by nitrogen fixation and IAA functions. On the basis of culture and morphological characteristics and 16S rDNA sequence, MS-43 was identified as a strain of Paenibacillus.