Biocontrol efficiency and potential mechanism of Bacillus subtilis GNRP-01A against Astragalus mongholicus root rot

Astragalus mongholicus is a well-known traditional Chinese herbal medicine with a long history of medicinal use, while root rot caused by Fusarium oxysporum is a highly destructive soil-borne diseases that leads to yield and quality reduction. Although previous studies have demonstrated that the biocontrol strategy based on microbial agents could effectively inhibit root rot in crops, the biocontrol efficiency and potential mechanism in A. mongholicus have been rarely investigated. In this study, a novel strain GNRP-01A was isolated from the rhizosphere of wild A. mongolicus and exhibited significant biocontrol efficacy (77.8 %) against A. mongolicus root rot, which was identified as Bacillus subtilis based on morphology, 16S rRNA, and whole-genome sequence analyses. The B. subtilis GNRP-01A genome contained multiple biosynthetic gene clusters encoding secondary metabolites ( e.g., surfactin, subtilosin A, bacillibactin) and the genes that promote plant growth ( e.g., amylase, protease, cellulase). Additionally, GC-MS analysis identified 13 volatile organic compounds (VOCs), among which 2-dodecanone, 2-tridecanone, and 6-methyl-2-heptanone showed strong antifungal activities with inhibition rates of 81.53 %, 89.17 %, and 91.86 %, respectively. Moreover, the expression levels of genes associated with plant induced systemic resistance (ISR , e.g. , AmCHI2 , AmPAD4 , AmPDF2.2 and AmPR-10 ) were significantly up-regulated in F. oxysporum + GNRP-01A treated plants, indicating the activation of ISR of A. mongolicus . Collectively, B. subtilis GNRP-01 A controls A. mongholicus root rot through synergistic strategy involving the production of antifungal metabolites and VOCs, activation of plant ISR. These results provide new insights into the biocontrol mechanism of B. subtilis against A. mongholicus root rot, as well as support the potential applications of B. subtilis GNRP-01A as an effective biocontrol agent for root rot prevention and management in medicinal plants.