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Root rot of Panax notoginseng has received great attention due to its threat on the plantation and sustainable utilization of P. notoginseng. To suppress the root-rot disease, natural ingredients are of great importance because of their environment friendly properties. In this study, we found that the methanol extract from Artemisia annua leaves has strong antifungal effects on the growth of Fusarium oxysporum and Fusarium solani resulting into root-rot disease. Essential oil (EO) thereof was found to be the most active. GC-MS analysis revealed 58 ingredients and camphor, camphene, β-caryophyllene, and germacrene D were identified as the major ingredients. Further antifungal assays showed that the main compounds exhibit various degrees of inhibition against all the fungi tested. In addition, synergistic effects between A. annua EO and chemical fungicides were examined. Finally, in vivo experiments were conducted and disclosed that P. notoginseng root rot could be largely inhibited by the petroleum ether extract from A. annua, indicating that A. annua could be a good source for controlling P. notoginseng root-rot.

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Chemical agents in the rhizosphere soils of plants might have an influence on root-rot disease, which therefore might reveal the mechanism of root rot in Panax notoginseng (P. notoginseng). With this hypothesis the alterations of phenolic acids (PAs) in the rhizosphere soils of P. notoginseng after pathogen infection were determined. The effects of PAs on the growth of Fusarium oxysporum (F. oxysporum), a fungal pathogenic factor for P. notoginseng, as well as production of fusaric acid, a wilting agent for the plants, were also examined. The results indicate the presence of five PAs (ferulic acid, syringic acid, p-hydroxybenzoic acid, p-coumaric acid, and vanillic acid) in the rhizosphere soils of P. notoginseng, whose contents in the rhizosphere soils of healthy plants are higher than those of the diseased ones. Further we found that individual PA could inhibit the mycelium growth and spore production of F. oxysporum, but stimulate fusaric acid production as well, disclosing the double-edge sword role of PAs in the occurrence of root rot of P. notoginseng and paving the way for the intervention of P. notoginseng root rot via balancing PAs.

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