Inoculation with Penicillium citrinum aids ginseng in resisting Fusarium oxysporum by regulating the root and rhizosphere microbial communities

Ginseng root rot disease caused by Fusarium oxysporum severely decreases root yield and quality, causing huge economic losses. Biological control is safe, environmentally friendly and sustainable. The results from bananas, sunflowers and chickpeas showed that Penicillium citrinum could control root diseases. However, its potential to control root rot disease of the medicinal plant is unclear. Here, the effects of P. citrinum YW322 isolated from ginseng rhizosphere soil on controlling root rot disease of ginseng were evaluated using the pot experiment. Four treatments were set up: no inoculation (CK), P. citrinum inoculation (PC), F. oxysporum inoculation (FO) and mixed inoculation of P. citrinum and F. oxysporum (PCFO). The results showed that the PC treatment did not affect ginseng growth when compared with the CK treatment. The plants in FO grew more slowly and rotted more severely. Distinct from FO, the ginseng plants in the PCFO treatment all grew similarly to CK. Plate confrontation experiments showed that P. citrinum YW322 inhibited the mycelium growth of F. oxysporum YFW32 by 95.75%. After 7 days of cultivation, the filtrate secreted nonvolatile inhibitory substances with 58.82% inhibition. The results from high-throughput sequencing showed that the structure of the bacterial community in ginseng roots and the fungal community in rhizosphere soil in the PCFO treatment were significantly different compared to the FO treatment (p < 0.05). Compared with FO, the abundance of Clostridium was significantly suppressed in the ginseng roots of PCFO treatment (93.5% reduction) (p < 0.05); significant enrichment of fungi such as Mortierella, Trichoderma and Penicillium was observed in ginseng rhizosphere soil in the PCFO treatment (8.26%, 17.44% and 2.80% increase in relative abundance, respectively). The relative abundance of the pathogenic fungus Fusarium decreased 31.85% compared with FO (p < 0.05). Soil physicochemical analysis showed that compared to the FO treatment, the soil pH and S-CAT activity in the PCFO treatment significantly increased (p < 0.05). Therefore, P. citrinum has potential to control ginseng root rot disease by directly inhibiting the growth of F. oxysporum and regulating the community structure of root bacteria and rhizosphere fungi to help ginseng resist F. oxysporum.