Rhizospheric ginsenosides released from roots infected with root rot improve infectivity of pathogenic Fusarium fungi in ginseng

Abstract

Root rot caused by infection with pathogenic fungi is a major disease of cultivated ginseng. In this study, we analyzed microbial diversity and found that the abundance of fungi of the genus Fusarium was the highest in the samples of ginseng with root rot from Tonghua, accounting for 29.84 ± 14.76 % of the total diversity. Eight strains of pathogenic Fusarium spp. fungi were isolated and identified, of which F. verticillioides ga-10 exhibited the strongest infectivity. Ginsenosides Rb₁, Rd, Rg₂, Rg₁, and Re were found using UPLC-MS/MS analyses to be abundant in the rhizospheric soil of ginseng suffering from root rot. Using a nutrient co-culture method, we demonstrated that the ginsenoside Rb₁ had a significant inhibitory effect on the mycelial growth of F. vanettenii ga-2 at 256 μg/mL. Using a non-nutritive co-culture method, we found that ginsenosides Rb₁, Rd, Rg₁, Rg₂, and Re all promoted the spore germination of F. oxysporum ga-11, and the ginsenosides Rd and Rg₁ promoted spore germination in F. solani ga-3 and F. vanettenii ga-13, respectively. In addition, the ginsenosides Rd, Rg₁, Rg₂, and Re all promoted spore germination in the most virulent strain ga-10. Ginseng is therefore able to exhibit a certain defensive ability against pathogenic fungi through the release of ginsenosides, however, Fusarium spp. can adapt to and use these ginsenosides. This study provides evidence for ginsenosides as the indicative substances of pathogenic fungal infection in ginseng roots.