Abstract: Using Alternaria longipes as tested phytopathogen, endophytic bacteria isolated from soybean nodules were selected to study antagonistic effects by confrontation and metabolic liquid culture methods. The inhibited hyphae were determined by microscopic observation, and the screened strains were characterized by cell culture, physiological and biochemical tests, 16S rDNA sequencing, phylogenetic analysis and inoculation trials in greenhouse. The results indicated that the seven of the endophytes exerted more than 42% inhibitory effects after the first and the second screening. These strains belonged to genus Bacillus, Pseudomonas, Sinorhizobium and Stenotrophomonas, respectively. Microscopic observation showed that the affected hyphae ends of A. longipes appear deformity of coralline branch, spherical expansions and so on. Antagonistic experiments with metabolites showed that the inhibition of endophytic bacteria against pathogenic fungus played an effective role mainly by bacteria producing extracellular substances. Confrontation tests suggested that endophytic Bacillus rapidly produced biofilm to effectively hinder the growth and extension of pathogen hyphae. Inoculation experiments showed that the disease index of treatment group was significantly lowered compared with the control, suggesting it could be utilized as a biological control resource inhibiting tobacco brown spot.

Key words: Alternaria longipes, phylogenetic analysis, 16S rDNA sequencing, biocontrol., endophytic bacteria of root nodules