Selective effects of ginseng fibrous root necromass on the fungal community in the rhizosphere and the related mechanism of ginseng replant disease

Abstract

Background Ginseng replant disease is thought to originate from several fungal pathogens accumulated in rhizosphere soil. The accumulative factors have attracted many research interests. A plant’s root system releases considerable fine root necromass to the rhizosphere. The root biomass of Panax spp. has a fast-decomposing rate. It should be more suitable for ginseng’s pathogenic enrichment for the host-pathogen relationship. However, the effects of the root necromass on the soil fungal community have yet to attract any research interest. This job investigates whether ginseng fibrous root necromass on the soil fungal community is selective. Methods Ginseng fibrous roots were mixed into fresh sands and incubated under a simulated ground condition in a ginseng garden. The aerial part of alfalfa and fried ginseng fibrous root were used as the controls. The soils from the maize and soybean garden were used to validate the results observed from the sands. The soil fungi were identified and compared by fungal Internal Transcribed Spacer Identification sequencing. Results All biomasses-treated soils showed significant selective enrichment effects on corresponding fungi in their respective communities. The soils treated with ginseng fibrous roots displayed the most significant impact on their root pathogenic fungal enrichment. The richness of the most common root pathogenic fungi, Cephalotrichum, Fusarium, and Paraphoma, in the soils treated with ginseng fibrous root powder increased to 12.5%, 4.5%, and 1.1% (36.3, 12.7 and 2.5 times as compared to the control) respectively. At the species level, the pathogenic fungi of Cephalotrichum asperulum, Fusarium oxysporum, and Paraphoma rhaphilepidis increased to 6.6%, 4.3%, and 1.1% (38.6, 654.4, and 10.0 times) respectively in abundance. Fried ginseng fibrous root lost their effect of pathogenic fungi enrichment. Conclusion Ginseng root pathogenic fungi were selectively enriched and became the dominant taxa in the soil containing the biomass of ginseng fibrous root. Most previous approaches for replant disease management aimed for sterilization; however, the pathogens were raised after some time because there were sufficient substances for their regeneration. Our results suggested that depletion of the root necromass should be a much more effective method for replant disease management.