Screening, identification and fermentation optimization of an antagonistic actinomycete strain XL-6 against Ralstonia solanacearum

Abstract:

[Background] Bacterial wilt was a destructive soil borne disease without effective chemical pesticides to prevent. While antagonistic actinomycetes had many successful application on a variety of plant disease with environmental protection and no residual, which provided a new way for the biological control of bacterial wilt in eggplant. [Objective] We isolate and screen antagonistic actinomycetes strains with inhibitory activity on Ralstonia solanacearum from the rhizosphere soil of healthy eggplants. [Methods] Actinomycete was isolated by Pour Plate method. Antagonistic actinomycete was screened by double agar layer plaque technique, agar diffusion assay and confrontation culture in vitro. Strain XL-6 was identified by morphological, culture, physiological and biochemical characteristics and 16S rRNA gene sequence analysis. The fermentation condition was optimized by single factor and orthogonal experiment. [Results] Strain XL-6 showed antagonistic to Ralstonia solanacearum and three other pathogens. Strain XL-6 belonged to Streptomyces rochei. The optimum culture conditions of strain XL-6 was with a medium of 30.0 g cornmeal, 5.0 g yeast powder, 2.0 g K2HPO4, 2.0 g MgCl2, 1.0 g NaCl in 1 000 mL filtrate water at initial pH of 7.0, liquid volume 70 ml in 250 ml flask, 180 r/min at 28 °C, inoculation size of 6% for 6 d. [Conclusion] Strain XL-6 was identified as Streptomyces rochei and showed stronger antagonistic action to Ralstonia solanacearum under optimized fermentation conditions.