Autotoxic Ginsenoside Disrupts Soil Fungal Microbiomes by Stimulating Potentially Pathogenic Microbes

Abstract

Autotoxic ginsenosides have been implicated as one of the major causes for replant failure of Sanqi ginseng (Panax notoginseng); however, the impact of autotoxic ginsenosides on the fungal microbiome, especially on soilborne fungal pathogens, remains poorly understood. In this study, we aimed to investigate the influence of the ginsenoside monomers Rg₁, Rb₁, and Rh₁, and that of their mixture (Mix), on the composition and diversity of the soil fungal community, as well as on the abundance and growth of the soilborne pathogen Fusarium oxysporum in pure culture. The addition of autotoxic ginsenosides altered the composition of the total fungal microbiome, as well as the taxa within the shared and unique treatment-based components, but did not alter alpha diversity (α-diversity). In particular, autotoxic ginsenosides enriched potentially pathogenic taxa, such as Alternaria, Cylindrocarpon, Gibberella, Phoma, and Fusarium, and decreased the abundances of beneficial taxa such as Acremonium, Mucor, and Ochroconis Relative abundances of pathogenic taxa were significantly and negatively correlated with those of beneficial taxa. Among the pathogenic fungi, the genus Fusarium was most responsive to ginsenoside addition, with the abundance of Fusarium oxysporum consistently enhanced in the ginsenoside-treated soils. Validation tests confirmed that autotoxic ginsenosides promoted mycelial growth and conidial germination of the root rot pathogen F. oxysporum In addition, the autotoxic ginsenoside mixture exhibited synergistic effects on pathogen proliferation. Collectively, these results highlight that autotoxic ginsenosides are capable of disrupting the equilibrium of fungal microbiomes through the stimulation of potential soilborne pathogens, which presents a significant hurdle in remediating replant failure of Sanqi ginseng.IMPORTANCE Sanqi ginseng [Panax notoginseng (Burk.) F. H. Chen] is geoauthentically produced in a restricted area of southwest China, and successful replanting requires a rotation cycle of more than 15 to 30 years. The increasing demand for Sanqi ginseng and diminishing arable land resources drive farmers to employ consecutive monoculture systems. Replant failure has severely threatened the sustainable production of Sanqi ginseng and causes great economic losses annually. Worse still, the acreage and severity of replant failure are increased yearly, which may destroy the Sanqi ginseng industry in the near future. The significance of this work is to decipher the mechanism of how autotoxic ginsenosides promote the accumulation of soilborne pathogens and disrupt the equilibrium of soil fungal microbiomes. This result may help us to develop effective approaches to successfully conquer the replant failure of Sanqi ginseng.

Keywords: Panax notoginseng; allelopathic effect; autotoxic ginsenosides; fungal disequilibrium; soilborne pathogen.