Biocontrol effects and underlying mechanism of Bacillus subtilis Pn1 on Panax notoginseng root rot caused by Fusarium solani

Panax notoginseng, a valuable plant used in traditional Chinese medicine, is often difficult to cultivate because of its susceptibility to various diseases, including root rot. In this study, an antagonistic bacterium (Pn1), which was identified as Bacillus subtilis, effectively controlled P. notoginseng root rot. The underlying mechanism in B. subtilis Pn1 was analyzed. The Pn1 culture supernatant had inhibitory effects on the root rot pathogen Fusarium solani and down-regulated the expression of pathogenicity-related genes. A liquid chromatography-tandem mass spectrometry analysis indicated that Pn1 produces many antifungal metabolites effective against F. solani. Additionally, proteins extracted from the Pn1 culture supernatant adversely affected F. solani mycelial growth and spore germination. Moreover, a proteomic analysis identified several antifungal proteins and antibiotic-related synthases. Furthermore, transcriptome and metabolome analyses of P. notoginseng suggested that B. subtilis Pn1 may protect against root rot through a mechanism involving the activation of phytohormone and phenylpropanoid/flavonoid biosynthesis pathways. This study reports, for the first time, the in-depth and multifaceted mechanisms on the application of B. subtilis in controlling P. notoginseng root rot. The study findings may lead to the application of B. subtilis Pn1 to enhance P. notoginseng root rot resistance, with potential implications for the development of more advanced disease control methods.