Characterization of Bacillus velezensis XG2 from Angelica sinensis rhizosphere and its effects on plant growth, secondary metabolism, and biocontrol against root rot

A rhizobacterial strain, Bacillus velezensis XG2, isolated from the rhizosphere of Angelica sinensis (Oliv.) Diels, was identified through 16S rRNA gene sequencing and whole-genome sequencing. XG2 produced siderophores and exopolysaccharides, and significantly enhanced seed germination, plant height (17.27 %), and shoot biomass (59.14 %) in A. sinensis . Confocal microscopy confirmed stable root colonization, and DHE fluorescence imaging showed increased intracellular ROS, along with enhanced antioxidant enzyme activities (POD + 77.20 %, CAT + 102.39 %). Chlorophyll content also increased significantly. UPLC–MS analysis revealed an 83.91 % reduction in ferulic acid, supported by qRT-PCR data showing downregulation of PAL and COMT expression. UPLC–MS identified ligustilide, 3-n-butylphathlide, and butylidene phthalide as key metabolites produced by B. velezensis XG2. Dual-culture assays showed antifungal activity with inhibition rates of 38.38 % against Mucor circinelloides and 46.25 % against Fusarium tricinctum . Overall, B. velezensis XG2 serves as a multifunctional bioinoculant, designed to promote growth, enhance antioxidant defense, and control root rot diseases in A. sinensis . However, it also reduces ferulic acid biosynthesis, indicating a growth-defense trade-off, which is an important consideration in the cultivation of medicinal plants.