Identification, fermentation condition optimization, and effect of a strain against Sclerotium rolfsii in Aconitum carmichaeli

Abstract:

[Background] Southern blight of Aconitum carmichaeli is a soil-borne bacterial disease caused by Sclerotium rolfsii, which seriously affects the production of the medicinal plant. [Objective] To screen a strain against the S. rolfsii in A. carmichaeli and use it for disease control. [Methods] The strains were isolated from Tenebrio molitor pupae by plate coating method and streak plate method. The strain with strong ability against S. rolfsii was identified by plate confrontation assay, and the taxonomic status was determined based on morphological observation, physiological and biochemical tests, and 16S rRNA sequencing. Fermentation conditions were optimized by single factor test. The inhibitory effect of suspension, volatile gas, and fermentation broth of the antagonistic strain on the mycelia of S. rolfsii was determined. [Results] An efficient antagonistic strain N2 was screened out and identified as Bacillus siamensis. The best medium formula (g/L) of strain N2 is tryptone 10.0, yeast extract 5.0 and sucrose 20.0. The optimum culture conditions were as follows:initial pH 6.0, temperature 36℃, rotating speed 240 r/min, liquid volume 30 mL, and inoculum 0.05%. The suspension, volatile gas, and fermentation broth of the strain all can effectively inhibit the growth of S. rolfsii mycelia. The results of extracellular enzyme assay showed that the strain could produce protease and cellulase but failed to synthesize siderophore. [Conclusion] Strain N2 has ideal inhibitory effect on S. rolfsii of A. carmichaeli, which has a good application potential and high research value in biological control.

Key words:southern blight of Aconitum carmichaeli;Bacillus siamensis;optimization of fermentation conditions;inhibitory effect;biological control