Identification and activity of Streptomyces sp. 21-6 against Fusarium graminearum

Abstract:

[Background] Fusarium graminearum is one of the main fungal pathogens in wheat production.[Objective] To isolate and screen Streptomyces strains against F. graminearum and lay a theoretical foundation for the biological control. [Methods] Streptomyces strains were isolated with the dilution-plating method, and a plate confrontation experiment was conducted to screen out the strains with antagonistic effects on F. graminearum. The strain was identified based on morphological, physiological and biochemical characteristics, and sequence analysis of 16S rRNA gene. The mycelial growth rate method was used to analyze the fermentation conditions and the stability of the cell-free fermentation broth. The biocontrol effect and antifungal spectrum of the strain 21-6 were also evaluated.[Results] Strain 21-6, which was finally identified as Streptomyces stelliscabiei, showed inhibitory effect on F. graminearum, with the inhibition rate of 75.2%±2.1%. The optimized fermentation conditions for the antifungal activity were PDB medium, fermentation time of 5 days, and initial pH 7.0. The cell-free fermentation suppressed both the mycelial growth and conidial germination of F. graminearum. The antifungal activity of cell-free fermentation broth was free from high temperature, pepsin, trypsin, and proteinase K. However, the fermentation broth was resistant to acidic but sensitive to alkali environment. Moreover, the broth inhibited the infection of wheat coleoptiles by F. graminearum. Strain 21-6 harbors polyketide synthase pks-Ⅰ and pks-Ⅱ genes. It showed biological activities against five plant pathogenic fungi. [Conclusion] Strain 21-6 has a promising prospect in the biological control of F. graminearum.