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Essential oils (EOs) have been proposed as an alternative to conventional pesticides to inhibit fungal pathogens. However, the application of EOs is considerably limited due to their highly volatile nature and unpredictable effects on other microbes. In our study, the composition of bacterial and fungal communities from the rhizosphere soil of P. notoginseng under four treatment levels of Alpinia officinarum Hance EO was characterized over several growth stages. Leaf weight varied dramatically among the four EO treatment levels after four months of growth, and the disease index at a low concentration (0.14 mg/g) of EO addition was the lowest among the P. notoginseng growth stages. The content of monomeric saponins was elevated when EO was added. Bacterial and fungal diversity in the absence of plants showed a decreasing trend with increasing levels of EO. Bacterial diversity recovery was more correlated with plant growth than was fungal diversity recovery. Compared with the control (no EO addition), a low concentration of EO significantly accumulated Actinomycota , including Acidothermus , Blastococcus , Catenulispora , Conexibacter , Rhodococcus , and Sinomonas , after one month of plant-microbial interaction. Overall, the results showed that both the plant growth stage and EOs drive changes in the microbial community composition in the rhizosphere of P. notoginseng . Plant development status had a stronger influence on bacterial diversity than on fungal diversity. EO had a more significant effect on fungal community composition, increasing the dominance of Ascomycota when EO concentration was increased. Under the interaction of P. notoginseng growth and EO, a large number of bacterial genera that have been described as plant growth-promoting rhizobacteria (PGPR) responded positively to low concentrations of EO application, suggesting that EO may recruit beneficial microbes in the root zone to cope with pathogens and reduce root rot disease. These results offer novel insights into the relationship between EO application, altered microbial communities in the plant roots, plant growth stage, and disease occurrence.

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.

Replanting obstacles of Panax notoginseng caused by complex factors, including pathogens, have received great attention. In this study, essential oils (EOs) from either Alpinia officinarum Hance or Amomum tsao-ko (Zingiberaceae) were found to inhibit the growth of P. notoginseng -associated pathogenic fungi in vitro. Subsequent GC-MS analysis revealed the chemical profiles of two plant derived EOs. Linalool and eucalyptol were found to be abundant in the EOs and tested for their antifungal activities. In addition, the synergistic effects of A. tsao-ko EOs and hymexazol were also examined. These findings suggested that Zingiberaceae EOs might be a good source for developing new green natural pesticides fighting against root-rot of P . notoginseng .

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., Competing Interests: The authors declare no conflict of interest.

Pseudolarolides U and V, two new triterpenoids, and four biogenetically related compounds, pseudolarolides E, F, K, and P were isolated from the roots of Codonopsis pilosula (Campanulaceae). Their structures were determined by spectroscopic data. The regulation of Sirtuin 1 (SIRT1) activity by all the isolated compounds was evaluated., Competing Interests: The authors declare that there is no conflict of interest.