10.5 billion CFU /g Paenibacillus polymyxa and Bacillus subtilis wettable powder: a novel fungicide for controlling Rhizoctonia solani by colonizing, reshaping the phyllosphere microbial community and inducing plant resistance

BACKGROUND Our laboratory participated in the development of a 10.5 billion colony‐forming units (CFU) g –1 Paenibacillus polymyxa and Bacillus subtilis wettable powder (PBM), which has been registered in China as a novel microbial fungicide. Subsequent research has demonstrated that PBM exhibits significant inhibitory effects on tobacco target spot disease caused by Rhizoctonia solani , yet the underlying mechanisms remain unclear. RESULTS PBM effectively inhibits the mycelial growth of R. solani and induces morphological distortions in the fungal hyphae. Field trials demonstrated that PBM provid a control efficiency of 86.03 ± 1.76% against R. solani . Additionally, PBM enhanced agronomic traits of the plants, including height, leaf length and leaf width. Analysis of the phyllosphere microbial community revealed that application of PBM to the abaxial surface of leaves under high humidity conditions at 28 °C facilitates the colonization of biocontrol bacteria. Moreover, PBM not only significantly reducedthe abundance of pathogenic microorganisms including R. solani , but also promote the enrichment of beneficial microbial communities on the leaf surface, thereby restoring the microbial community structure to a state resembling that of healthy plants. Furthermore, PBM treatment stimulated host resistance responses by inducing the expression of defense‐related genes and upregulating the activity of defense‐related enzymes. CONCLUSION This study elucidates the functions and mechanisms of the composite microbial pesticide PBM, underscoring its potential as an environmentally friendly biological control agent against plant diseases caused by R. solani .