An antagonistic bacterial strain CZ1 against southern blight on Aconitum carmichaelii: isolation, identification, optimization of fermentation conditions, and evaluation of control effect

Abstract:

[Background] Southern blight is a soil-borne disease caused by Sclerotium rolfsii, causing serve loss to Aconitum carmichaelii production. [Objective] To clarify the taxonomic status of an antagonistic strain CZ1 against S. rolfsii, and optimize the fermentation conditions to maximize the control effect on southern blight of A. carmichaelii. [Methods] The dilution-plate coating method was employed to isolate bacteria from the Malpighian tubules of Cantheconidae furcellata. The plate confrontation assay was employed to screen out the strain with strong resistance to S. rolfsii, and the inhibitory effects of this strain on other plant pathogenic fungi were determined. The taxonomic status of the strain was determined based on morphological characteristics, physiological and biochemical properties, and 16S rRNA gene sequence. With OD₆₀₀ value of the fermentation broth as the indicator, single factor and orthogonal experiments were carried out to optimize the medium components and fermentation conditions. Furthermore, indoor pot experiment was carried out to evaluate the control effect of the strain. [Results] Six strains of bacteria were isolated, among which CZ1 had the highest inhibition rate on S. rolfsii. CZ1 had inhibitory effects on other plant pathogenic fungi such as Phytophthora nicotiana and Fusarium oxysporum and was preliminary identified as Bacillus subtilis. The optimal culture medium was composed of 15.00 g/L sucrose, 25.00 g/L peptone, and 7.50 g/L yeast extract. The strain showed the highest biomass when cultured at the inoculation amount of 2%, liquid loading volume of 90 mL, 210 r/min, 36 ℃, and initial pH 8.0 for 120 h. The results of indoor pot experiment showed that the average control efficiency of CZ1 against the southern blight on A. carmichaelii reached 59.26%. [Conclusion] CZ1 strain has good potential in the biocontrol of southern blight on A. carmichaelii.