Comparative response of root-associated soil bacterial communities to phytophthora blight in healthy versus diseased Panax notoginseng plants

Phytophthora blight of Panax notoginseng caused by the fungal pathogen Phytophthora cactorum is a typical soilborne disease, that severely devastates the P. notoginseng industry, and soil bacterial diversity is closely related to the development of Phytophthora blight. A systematic investigation into the abundance of Phytophthora spp. as well as the structural and functional characteristics of the soil bacterial community was carried out using quantitative PCR, high-throughput sequencing of the bacterial 16 S rRNA gene, and KEGG pathway analysis. Results showed Phytophthora spp. was most abundant in the rhizosphere soil of diseased plants (RSD) (9.3017 copies ng⁻¹ DNA) and least in the rhizosphere soil of healthy plants (RSH) (0.0169 copies ng⁻¹ DNA). For bacterial α-diversity, ACE and Chao1 indices of diseased soils (RSD and root-zone soil of diseased plants, ZSD) were significantly higher than healthy soils (RSH and root-zone soil of healthy plants, ZSH) and furrow soil (FS) (p < 0.05), with no difference in Shannon index (p > 0.05). β-diversity analyses revealed distinct clustering of the same soil type and inter-group compositional differences. Dominant taxa analysis showed higher Actinomycetota and Bacteroidota in healthy soils, while Verrucomicrobiota, Planctomycetota, and Ramlibacter were more abundant in diseased soils. KEGG functional analysis indicated that the abundances of the "Signal transduction" and "Membrane transport" pathways in the RSD group were higher than those in other groups, while the abundances of the "Metabolism of terpenoids and polyketides" and "Biosynthesis of other secondary metabolism" pathways in the RSD group were lower than those in healthy soils. This suggests that the lack of microorganisms synthesizing anti-oomycete secondary metabolites may contribute to the enrichment of pathogens in the RSD group. This study reveals the association mechanisms between the abundance of soil pathogens, bacterial community structure, and functions in P. notoginseng soils, providing a theoretical basis for the prevention and control of soil-borne diseases and the regulation of soil microecology in P. notoginseng cultivation.