Abstract: In order to find potential biocontrol strains, 123 strains of actinomycetes were isolated and screened from soil by preliminary co-culture screening and Oxford cup re-screening. Ultimately, the strain Sa-4 was obtained, which had the strongest inhibitory ability against the pathogen of common bacterial blight of beans, Xanthomonas axonopodis pv. phaseoli (Xap). The antibacterial ring diameter of its fermentation broth was (31.62±3.23) mm. Based on microscopic observation, physiological and biochemical characteristics determination combined with 16S rDNA sequence analysis, the strain Sa-4 was identified as Streptomyces avidinii. The results of antibacterial spectrum determination showed that the fermentation broth of strain Sa-4 had strong antagonistic effects on various plant pathogens. The results of stability test showed that the fermentation broth of strain Sa-4 had good light stability and thermal stability. The results of antibacterial mechanism study showed that the fermentation broth of strain Sa-4 had no significant effect on the genomic DNA of Xap but had a certain influence on the protein synthesis of Xap. Fourier-transform infrared spectroscopy showed that the fermentation broth of strain Sa-4 would cause changes in the substances on the surface of Xap cell membrane, while results of electron microscopy showed that Xap cells were shrinked and depressed. The relative control efficacy of strain Sa-4 fermentation broth against common bacterial blight of beans could reach 68.69% by pot experiment. The results of this study provided basic reference data for the biocontrol products development of Streptomyces avidinii strain Sa-4 in common bacterial blight of beans.

Key words: Streptomyces avidinii, common bacterial blight of beans, screening and identification, biocontrol