Pathogenicity Profiling and Biocontrol of Fusarium Species Causing Root Rot in Panax Notoginseng

Abstract

Fusarium accumulation considerably contributes to root rot in Panax notoginseng, hindering its continuous cropping. However, the pathogenicity and potential mechanisms of different Fusarium species that cause root rot in P. notoginseng remain unclear. Herein, we aimed to isolate and identify the Fusarium species responsible for P. notoginseng root rot, compare their pathogenicity, explore pathogenic mechanisms, and screen potential biocontrol strains. To this end, in vitro and pot experiments were performed to compare the pathogenicity of Fusarium species, measure the activities of cell wall-degrading enzymes (CWDEs), and quantify the abundance of Fusarium species in different niches. Ultimately, potential biocontrol microorganisms were screened. Three distinct Fusarium species, namely, Fusarium oxysporum LP1, Fusarium solani LP2, and Fusarium solani LP3, were isolated from the soil of continuously cropped P. notoginseng in Lancang County, Yunnan Province. Among these, LP2—a new physiological race of F. solani—exhibited the strongest pathogenicity. Moreover, the CWDEs produced by F. solani exhibited higher activities than those produced by F. oxysporum. However, the content of F. oxysporum was greater than that of F. solani within the three niches (root tissue, rhizosphere soil, and bulk soil). Additionally, two Fusarium antagonists, Penicillium glabrum LZ-3 and Penicillium polonicum LZ-6, were identified. Both demonstrated the ability to reduce the incidence of root rot caused by F. solani LP2 and increase biomass accumulation in P. notoginseng. LZ-3 markedly increased the contents of saponins Rg1, Rb1, Rd, and R1 and the activities of peroxidase and phenylalanine aminolase in P. notoginseng. LZ-3 can also induce Fusarium peroxidation stress. In conclusion, F. solani exhibits greater pathogenicity than F. oxysporum owing to its higher CWDE activity. Meanwhile, F. oxysporum content is greater than that of F. solani in the niche, offering a population advantage. Furthermore, Penicillium spp. can induce systemic resistance in plants and induce oxidative stress in Fusarium to biologically control the root rot caused by Fusarium. These findings lay a theoretical foundation for the targeted control of root rot in P. notoginseng.

Keywords: Fusarium, root rot, Panax notoginseng, cell wall degrading enzyme (CWDE), penicillium, biocontrol