Abstract:[Background] Walnut blight is a serious bacterial plant disease caused by two pathogens, it lacks effective biological control method at present. [Objective] To isolate and screen antagonistic actinomycetes strains with inhibitory activity on walnut blight from the rhizosphere soil of walnut tree. [Methods] Actinomycete was isolated by using dilution plate coating. The methods of agar disk and improved Oxford-cup test were applied to screen antagonistic strains against Xanthomonas campestris pv. campestris and Pantoea agglomerans. The morphological, physiological, biochemical characteristics combined with 16S rRNA gene sequences were used for classification and identification. The antibacterial spectrum and the biocontrol effect of the cell-free fermentation broth were evaluated. [Results] Strain WMF106 had antagonistic effects on X. campestris pv. campestris with inhibition zone diameter of 2.38 cm and on P. agglomerans with inhibition zone diameter of 1.82 cm. The inhibition zone diameter of cell-free fermentation broth on X. campestris pv. campestris and P. agglomerans were 1.75 cm and 1.55 cm, respectively. Based on the morphological and physiological characteristics and 16S rRNA gene sequence analysis, strain WMF106 was identified as Streptomyces caeruleatus. The antibacterial spectrum experiment results indicated that Streptomyces caeruleatus WMF106 also showed biological activities against five species of plant pathogenic fungi (Fusarium oxysporum, Fusarium solani, Colletotrichum capsici, Botrytis cinerea and Colletotrichum gloeosporioides), and five species of indicator bacteria (Aspergillus niger, Monilia albican, Escherichia coli, Staphlococcus aureus and Pseudomonas aeruginosa). In addition, the biocontrol experiment in vitro showed that the cell-free fermentation broth of strain WMF106 had worthy prevention of walnut blight caused by X. campestris pv. campestris and P. agglomerans, and the biocontrol effects were 77.44% and 58.33%. [Conclusion] Strain WMF106 could be used for controlling the walnut blight, and have a wonderful potential for application.
