Abstract:[Background] Walnut blight, caused by Xanthomonas campestris and Pantoea agglomerans, is a bacterial disease resulting in severe damage to walnut tree and substantial economic loss. [Objective] To isolate and screen out the actinomycete strains with inhibitory activity on these two pathogens from the rhizosphere soil of walnut tree for the development of biocontrol agents. [Methods] The actinomycetes were isolated by spread plate method and further screened by plate confrontation method and improved Oxford-cup test. The target strain was identified based morphological, physiological, and biochemical properties, as well as 16S rRNA gene sequence. The antibacterial spectrum and biocontrol effect in vitro of the cell-free fermentation broth were evaluated. [Results] An actinomycete strain YNF36 with strong antagonistic effect on both pathogens was screened out and identified as Streptomyces arenae. The strain YNF36 showed antimicrobial activity to seven indicator bacterial species: Staphlococcus aureus, Escherichia coli, Aspergillus niger, Monilia albicans, Bacillus subtilis, Pseudomonas aeruginosa, and Bacillus cereus. Furthermore, it had inhibitory activity against seven plant pathogens: Alternaria alternata, Valsa mali, Colletotrichum gloeosporioides, Botrytis cinerea, Fulvia fulva, Colletotrichum capsica, and Fusarium solani. The strain YNF36 had the largest yield and the strongest antimicrobial activity on SYP medium. In addition, the biocontrol experiment in vitro showed that the cell-free fermentation broth of the strain YNF36 had the biocontrol effects of 75.69% and 62.39% against X. campestris and P. agglomerans, respectively. [Conclusion] The strain YNF36 could be considered as the actinomycete resource with biocontrol potential against walnut blight and demonstrates a wonderful prospect for development and application.
