Optimization of the Bacteriophage Cocktail for the Prevention of Brown Blotch Disease Caused by Pseudomonas tolaasii br

Brown blotch disease, caused by Pseudomonas tolaasii, is one of the most serious diseases in mushroom cultiva-tion, and its control remains an important issue. This study isolated and evaluated pathogen-specific bacterio- phages for the biological control of the disease. In previ-ous studies, 23 varieties of P. tolaasii were isolated from infected mushrooms with disease symptoms and clas-sified into three subtypes, Pt alpha, Pt , and Pt gamma, based on their 16S rRNA gene sequences analysis and pathogenic characters. In this study, 42 virulent bacteriophages were isolated against these pathogens and tested for their host range. Some phages could lyse more than two pathogens only within the corresponding subtype, and no phage exhibited a wide host range across different pathogen subtypes. To eliminate all pathogens of the Pt alpha, Pt , and Pt gamma subtype, corresponding phages of one, six, and one strains were required, respectively. These phages were able to suppress the disease completely, as confirmed by the field-scale on-farm cultivation experi- ments. These results suggested that a cocktail of these eight phages is sufficient to control the disease induced by all 23 P. tolaasii pathogens. Additionally, the anti-bacterial effect of this phage cocktail persisted in the second cycle of mushroom growth on the cultivation bed.