Targeted screening and functional evaluation of the bacterial antagonistics to Streptomyces scabies

Abstract:

Potato common scab (CS) caused by pathogenic Streptomycetes has occurred widely in China and led to increasing damage to the quality and commercial value of potato. Since the pathogen is soil-borne and seed-borne, antagonistic microorganisms are regarded as an important method for the prevention and control of this disease. [Objective] We aim to screen out the antagonistic bacterial strains from the soil in the field with serious CS, reveal the mechanism of antagonism against Streptomyces scabies, and evaluate the environmental adaptability of the targeted strains. This study can provide a theoretical basis for developing applicable microbial agents. [Methods] The strains with antagonistic effects were screened out via the plate confrontation method and pot experiment and then identified based on morphological, physiological, biochemical, and molecular characteristics. Their metabolites with antifungal functions were detected via high performance liquid chromatography coupled with mass spectrometry.[Results] Three Gram-positive strains with antagonistic effects were identified as Bacillus amyloliquefaciens and designated HZ11-4, HS-12, and HZ13-1, which showed the inhibition zone diameters of 34, 29 and 30 mm to S.scabies and the control effects of 68.57%, 57.15%, and 65.96%, respectively. The genes coding for synthetases of surfactin, iturin, and fengycin were amplified from these strains, and existence of the lipopeptide antibiotics was detected by high performance liquid chromatography. S.scabies could be inhibited only by surfactin which was not the main active compound of the strains. The three strains exerted inhibitory effects on a variety of pathogens such as Alternaria solani, Fusarium oxysporum, Rhizoctonia solani, and Verticillium dahliae. They could live in a wide pH range of 5-9, tolerate 1%-7% NaCl and high temperature of 100℃, promote potato growth, and were insensitive to fluopicolide + propamocarb, flusilazole, pyraclostrobin, kasugamycin, zhongshengmycin and thiophanate-methyl. [Conclusion] Owing to the good environmental adaptability and broad-spectrum resistance, B.amyloliquefaciens HZ11-4, HS-12, and HZ13-1 can be used to develop compound microbial agents against potato soil-borne diseases. This study verifies for the first time that surfactin, iturin A, and fengycin are not the main active substances to inhibit S.scabies.