Abstract: Aims: To isolate and screen the antagonistic strains with inhibitory activity against Pseudomonas syringae pv. actinidiae from a soil sample collected from the rhizosphere of kiwifruit in different areas and to optimize the fermentation conditions for enhanced production of antibacterial substances. Methods: Antagonistic strains were isolated by pour plate method, screened by inhibition zone method, and identified by morphological, physiological and biochemical characteristics and 16S rDNA sequence analysis. The optimal medium composition and fermentation conditions were optimized by one-factor-at-a-time and orthogonal array design methods. Results: A total of 288 actinomycetes strains were isolated, among which strain NA-TXL-1 exhibited the strongest inhibitory activity against Pseudomonas syringae pv. actinidiae. The effects of the fermentation broth in preventing and controlling Pseudomonas syringae pv. actinidiae in pot cultivated plants were 73.06% and 55.62%, respectively. Strain NA-TXL-1 was identified as Streptomyces antibioticus. The seed medium, inoculum size and initial pH value were optimized to be lactose-yeast power culture medium, 2%; and 7.0, respectively. The optimal culture medium consisted of 30 g/L lactose, 3 g/L yeast powder, 1 g/L NaCl, 0.5 g/L K2HPO4, 0.5 g/L MgSO4·7H2O, and 0.01 g/L FeSO4 at initial pH of 7.0. The optimal culture times for harvesting fermentation broth, the supernatant, and re-suspension were 5, 14, and 5 days, respectively. Conclusions: Strain NA-TXL-1 was identified as Streptomyces antibioticus, exhibiting stronger antagonistic effect under optimized fermentation conditions.

Key words: Pseudomonas syringae pv. actinidiae, antagonist, screening, identification, optimization of fermentation conditions