Effects of Essential Oils from Zingiberaceae Plants on Root-Rot Disease of Panax notoginseng

Terpenes modulate bacterial and fungal growth and sorghum rhizobiome communities

Terpenes are among the oldest and largest class of plant-specialized bioproducts that are known to affect plant development, adaptation, and biological interactions. While their biosynthesis, evolution, and function in aboveground interactions with insects and individual microbial species are well studied, how different terpenes impact plant microbiomes belowground is much less understood. Here we designed an experiment to assess how belowground exogenous applications of monoterpenes (1,8-cineole and linalool) and a sesquiterpene (nerolidol) delivered through an artificial root system impacted its belowground bacterial and fungal microbiome. We found that the terpene applications had significant and variable impacts on bacterial and fungal communities, depending on terpene class and concentration; however, these impacts were localized to the artificial root system and the fungal rhizosphere. We complemented this experiment with pure culture bioassays on responsive bacteria and fungi isolated from the sorghum rhizobiome. Overall, higher concentrations (200 µM) of nerolidol were inhibitory to Ferrovibrium and tested Firmicutes. While fungal isolates of Penicillium and Periconia were also more inhibited by higher concentrations (200 µM) of nerolidol, Clonostachys was enhanced at this higher level and together with Humicola was inhibited by the lower concentration tested (100 µM). On the other hand, 1,8-cineole had an inhibitory effect on Orbilia at both tested concentrations but had a promotive effect at 100 µM on Penicillium and Periconia. Similarly, linalool at 100 µM had significant growth promotion in Mortierella, but an inhibitory effect for Orbilia. Together, these results highlight the variable direct effects of terpenes on single microbial isolates and demonstrate the complexity of microbe-terpene interactions in the rhizobiome. IMPORTANCE Terpenes represent one of the largest and oldest classes of plant-specialized metabolism, but their role in the belowground microbiome is poorly understood. Here, we used a "rhizobox" mesocosm experimental set-up to supply different concentrations and classes of terpenes into the soil compartment with growing sorghum for 1 month to assess how these terpenes affect sorghum bacterial and fungal rhizobiome communities. Changes in bacterial and fungal communities between treatments belowground were characterized, followed by bioassays screening on bacterial and fungal isolates from the sorghum rhizosphere against terpenes to validate direct microbial responses. We found that microbial growth stimulatory and inhibitory effects were localized, terpene specific, dose dependent, and transient in time. This work paves the way for engineering terpene metabolisms in plant microbiomes for improved sustainable agriculture and bioenergy crop production.

Foliar Pathogen Infection Manipulates Soil Health through Root Exudate-Modified Rhizosphere Microbiome

Negative plant-soil feedback (NPSF) due to the buildup of soilborne pathogens in soil is a major obstacle in sustainable agricultural systems. Beneficial rhizosphere microfloras are recruited by plants, and mediating this has become a strategic priority to manipulate plant health. Here, we found that foliar infection of Panax notoginseng by Alternaria panax changed plant-soil feedback from negative to positive. Foliar infection modified the rhizosphere soil microbial community and reversed the direction of the buildup of the soilborne pathogen Ilyonectria destructans and beneficial microbes, including Trichoderma, Bacillus, and Streptomyces, in rhizosphere soil. These beneficial microbes not only showed antagonistic ability against the pathogen I. destructans but also enhanced the resistance of plants to A. panax. Foliar infection enhanced the exudation of short- and long-chain organic acids, sugars, and amino acids from roots. In vitro and in vivo experiments validated that short- and long-chain organic acids and sugars play dual roles in simultaneously suppressing pathogens but enriching beneficial microbes. In summary, foliar infection could change root secretion to drive shifts in the rhizosphere microbial community to enhance soil health, providing a new strategy to alleviate belowground disease in plants through aboveground inducement. IMPORTANCE Belowground soilborne disease is the main factor limiting sustainable agricultural production and is difficult to manage due to the complexity of the soil environment. Here, we found that aboveground parts of plants infected by foliar pathogens could enhance the secretion of organic acids, sugars, and amino acids in root exudates to suppress soilborne pathogens and enrich beneficial microbes, eventually changing the plant and soil feedback from negative to positive and alleviating belowground soilborne disease. This is an exciting strategy by which to achieve belowground soilborne disease management by manipulating the aboveground state through aboveground stimulation.

Root-Associated Microbiomes of Panax notoginseng under the Combined Effect of Plant Development and Alpinia officinarum Hance Essential Oil

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.

Characteristics and diversity of endophytic bacteria in Panax notoginseng under high temperature analysed using full-length 16S rRNA sequencing

Panax notoginseng is a traditional Chinese medicinal herb with diverse properties that is cultivated in a narrow ecological range because of its sensitivity to high temperatures. Endophytic bacteria play a prominent role in plant response to climate warming. However, the endophytic bacterial structures in P. notoginseng at high temperatures are yet unclear. In the present study, the diversity and composition of the endophytic bacterial community, and their relationships with two P. notoginseng plants with different heat tolerance capacities were compared using the full-length 16S rRNA PacBio sequencing system. The results revealed that the diversity and richness of endophytic bacteria were negatively associated with the heat tolerance of P. notoginseng. Beneficial Cyanobacteria, Rhodanobacter and Sphingomonas may be recruited positively by heat-tolerant plants, while higher amounts of adverse Proteobacteria such as Cellvibrio fibrivorans derived from soil destructed the cellular protective barriers of heat-sensitive plants and caused influx of pathogenic bacteria Stenotrophomonas maltophilia. Harmonious and conflicting bacterial community was observed in heat-tolerant and heat-sensitive P. notoginseng, respectively, based on the co-occurrence network. Using functional gene prediction of metabolism, endophytic bacteria have been proposed to be symbiotic with host plants; the bacteria improved primary metabolic pathways and secondary metabolite production of plants, incorporated beneficial endophytes, and combated adverse endophytes to prompt the adaptation of P. notoginseng to a warming environment. These findings provided a new perspective on the function of endophytes in P. notoginseng adaptation to high temperatures, and could pave the way for expanding the cultivable range of P. notoginseng.

Insights into the Composition and Antibacterial Activity of Amomum tsao-ko Essential Oils from Different Regions Based on GC-MS and GC-IMS

Chemical components are one of the most significant traits and attributes of plant tissues, and lead to their different functions. In this study, the composition of Amomun tsao-ko essential oils (AEOs) from different regions was first determined by a combination of gas chromatography–mass spectrometry (GC-MS) and gas chromatography–ion mobility spectrometry (GC-IMS). In total, 141 compounds were identified, of which terpenes and aldehydes were the main groups. Orthogonal partial least square discriminant analysis (OPLS-DA) distinguished the samples from different regions clearly, and the main differences were terpenes, aldehydes, and esters. Meanwhile, AEOs showed strong antibacterial activity against Staphylococcus aureus (S. aureus), and the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) reached 0.20 mg/mL and 0.39–0.78 mg/mL, respectively. From correlation analysis, 1,8-cineole, (E)-dec-2-enal, citral, α-pinene, and α-terpineol were determined to be the potential antibacterial compounds. This study provides the basis for the variety optimization of A. tsao-ko and its application as a natural food preservative.

Control of pathogenic fungi on Panax notoginseng by volatile oils from the food ingredients Allium sativum and Foeniculum vulgare

To screen natural drugs with strong inhibitory effects against pathogenic fungi related to P. notoginseng, the antifungal activities of garlic and fennel EOs were studied by targeting P. notoginseng disease-associated fungi, and the possible action mechanisms of garlic and fennel EOs as plant fungicides were preliminarily discussed. At present, the antifungal mechanism of EOs has not been fully established. Therefore, understanding the antifungal mechanism of plant EOs is helpful to address P. notoginseng diseases continuous cropping disease-related obstacles and other agricultural cultivation problems. First, the Oxford cup method and chessboard were used to confirm that the EOs and oxamyl had a significant inhibitory effect on the growth of Fusarium oxysporum. F. oxysporum is the main pathogen causing root rot of P. notoginseng and the preliminary study on the antifungal mechanisms of the EOs against F. oxysporum showed that the inhibition of EOs mainly affects cell membrane permeability, cell processes, and affects the enzyme activities of microorganism, to achieve antifungal effects. Finally an in vivo model verified that both two EOs could significantly inhibit the occurrence of root rot caused by F. oxysporum.

Amomum tsao-ko Crevost & Lemarié: a comprehensive review on traditional uses, botany, phytochemistry, and pharmacology

Tsaoko Fructus, the dried ripe fruit of Amomum tsao-ko Crevost & Lemarié, is used as both medicinal material and food additive. This review summarized the traditional uses, botany, phytochemistry, and pharmacological progress on Tsaoko Fructus. One classical prescription and the other 11 representative prescriptions containing Tsaoko Fructus were reviewed. The indications of these prescriptions are major in treating spleen and stomach disorders and epidemic febrile diseases including malaria. At least 209 compounds have been isolated and identified from Tsaoko Fructus, most of which belong to terpenoids, phenylpropanoids, and organic acids. Essential oil, crude extract, and some compounds were observed to have pharmacological activities such as anti-biotics, anti-inflammation, antioxidant, mostly via in vitro experiments. However, the mechanism of its medicinal uses remains unclear. This review provides a comprehensive understanding of Tsaoko Fructus, which will be beneficial to exploring the mechanism and potential medicinal applications of Tsaoko Fructus, as well as developing a rational quality control system for Tsaoko Fructus as a medicinal material in the future.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11101-021-09793-x.

Autotoxin Rg1 Induces Degradation of Root Cell Walls and Aggravates Root Rot by Modifying the Rhizospheric Microbiome

Management of crop root rot disease is one of the key factors in ensuring sustainable development in agricultural production. The accumulation of autotoxins and pathogens in soil has been reported as a primary driver of root rot diseases; however, less is known about the correlation of plants, their associated pathogens and microbiome mediated by autotoxins as well as the contributions autotoxins make to the occurrence of root rot disease. Here, we integrated metabolomic, transcriptomic, and rhizosphere microbiome analyses to identify the root cell wall degradants cellobiose and d-galacturonic acid as being induced by the autotoxic ginsenoside Rg₁ of Panax notoginseng, and we found that exogenous cellobiose and d-galacturonic acid in addition to Rg₁ could aggravate root rot disease by modifying the rhizosphere microbiome. Microorganisms that correlated positively with root rot disease were enriched and those that correlated negatively were suppressed by exogenous cellobiose, d-galacturonic acid, and Rg₁. In particular, they promoted the growth and infection of the soilborne pathogen Ilyonectria destructans by upregulating pathogenicity-related genes. Cellobiose showed the highest ability to modify the microbiome and enhance pathogenicity, followed by Rg₁ and then d-galacturonic acid. Collectively, autotoxins damaged root systems to release a series of cell wall degradants, some of which modified the rhizosphere microbiome so that the host plant became more susceptible to root rot disease.

IMPORTANCE The accumulation of autotoxins and pathogens in soil has been reported as a primary driver of root rot disease and one of the key factors limiting sustainable development in agricultural production. However, less is known about the correlation of plants, their associated pathogens, and the microbiome mediated by autotoxins, as well as the contributions autotoxins make to the occurrence of root rot disease. In our study, we found that autotoxins can damage root systems, thus releasing a series of cell wall degradants, and both autotoxins and the cell wall degradants they induce could aggravate root rot disease by reassembling the rhizosphere microbiome, resulting in the enrichment of pathogens and microorganisms positively related to the disease but the suppression of beneficial microorganisms. Deciphering this mechanism among plants, their associated pathogens, and the microbiome mediated by autotoxins will advance our fundamental knowledge of and ability to degrade autotoxins or employ microbiome to alleviate root rot disease in agricultural systems.

Enrichment of Burkholderia in the Rhizosphere by Autotoxic Ginsenosides to Alleviate Negative Plant-Soil Feedback

The accumulation of autotoxins and soilborne pathogens in soil was shown to be the primary driver of negative plant-soil feedback (NPSF). There is a concerted understanding that plants could enhance their adaptability to biotic or abiotic stress by modifying the rhizosphere microbiome. However, it is not clear whether autotoxins could enrich microbes to degrade themselves or antagonize soilborne pathogens. Here, we found that the microbiome degraded autotoxic ginsenosides, belonging to triterpenoid glycosides, and antagonized pathogens in the rhizosphere soil of Panax notoginseng (sanqi). Deep analysis by 16S rRNA sequencing showed that the bacterial community was obviously changed in the rhizosphere soil and identified the Burkholderia-Caballeronia-Paraburkholderia (BCP) group as the main ginsenoside-enriched bacteria in the rhizosphere soil. Eight strains belonging to the BCP group were isolated, and Burkholderia isolate B36 showed a high ability to simultaneously degrade autotoxic ginsenosides (Rb₁, Rg₁, and Rd) and antagonize the soilborne pathogen Ilyonectria destructans. Interestingly, ginsenosides could stimulate the growth and biofilm formation of B36, eventually enhancing the antagonistic ability of B36 to I. destructans and the colonization ability in the rhizosphere soil. In summary, autotoxic ginsenosides secreted by P. notoginseng could enrich beneficial microbes in the rhizosphere to simultaneously degrade autotoxins and antagonize pathogen, providing a novel ecological strategy to alleviate NPSF.

IMPORTANCE Autotoxic ginsenosides, secreted by sanqi into soil, could enrich Burkholderia sp. to alleviate negative plant-soil feedback (NPSF) by degrading autotoxins and antagonizing the root rot pathogen. In detail, ginsenosides could stimulate the growth and biofilm formation of Burkholderia sp. B36, eventually enhancing the antagonistic ability of Burkholderia sp. B36 to a soilborne pathogen and the colonization of B36 in soil. This ecological strategy could alleviate NPSF by manipulating the rhizosphere microbiome to simultaneously degrade autotoxins and antagonize pathogen.

Sesamol-based terpenoids as promising bio-sourced crop protection compounds against the wheat pathogen Zymoseptoria tritici

BACKGROUND

Research into environmentally friendly alternatives to conventional plant protection products, to promote sustainable agriculture and healthy food, is strongly encouraged.

RESULTS

In this context, 20 naturally occurring terpenoids and phenolic compounds were selected and evaluated in vitro as crop protection compounds against Zymoseptoria tritici, the causal agent of Septoria tritici blotch of wheat. After selection of the most active compounds, some hemisynthetic modifications were conducted to modify their lipophilicity. These modifications led to the discovery of sesamol esters as promising antifungal agents, with IC₅₀ around 10 μg/mL and a total absence of cytotoxicity against human cells.

CONCLUSION

These sesamol-based derivatives should be selected for further evaluations in planta to validate their use as wheat crop protection agents. Moreover, the importance of a balanced hydrophily/lipophilicity ratio should be further studied. © 2021 Society of Chemical Industry.

Chemical Composition of a Supercritical Fluid (Sfe-CO2) Extract from Baeckea frutescens L. Leaves and Its Bioactivity Against Two Pathogenic Fungi Isolated from the Tea Plant (Camellia sinensis (L.) O. Kuntze)

Colletotrichum gloeosporioides and Pseudopestalotiopsis camelliae-sinensis are the two most important tea plant (Camellia sinensis L.) pathogenic fungi. Interest in natural plant extracts as alternatives to synthetic chemical fungicides to control plant pathogens is growing. In this study, the volatile fraction of Baeckea frutescens L. was extracted by supercritical fluid extraction (SFE-CO₂), and its chemical composition was analyzed, and investigated for its antifungal activity against C. gloeosporioides and P. camelliae. The major constituents of the volatile fraction were β-caryophyllene (28.05%), α-caryophyllene (24.02%), δ-cadinene (6.29%) and eucalyptol (5.46%) in B. frutescens SFE-CO₂ extracts. The terpineol, linalool, terpinen-4-ol and eucalyptol showed strong contact antifungal activity against P. camelliae and C. gloeosporioides with median inhibitory concentration (MIC₅₀) in the range of 0.69 μL/mL to 2.79 μL/mL and 0.62 μL/mL to 2.18 μL/mL, respectively. Additionally, the volatile fraction had high fumigation antifungal activity against P. camelliae and C. gloeosporioides with an inhibition rate between 20.87% and 92.91%. Terpineol presented the highest antifungal activity in the contact and fumigation toxicity assays. Terpineol, linalool, terpinen-4-ol and eucalyptol were associated with the most active chemical compounds in the volatile fraction against the fungi. The results suggest that B. frutescens SFE-CO₂ extracts are potential ingredients to develop a natural fungicide for control of tea plant pathogens.

Analysis of the Endophytic Bacteria Community Structure and Function of Panax notoginseng Based on High-Throughput Sequencing

Panax notoginseng has long been used as a Chinese herb with high medicinal value. The endophytic bacteria in this medicinal plant have multiple biological functions. High-throughput sequencing is a rapidly evolving technique that helps profile the endophytic bacterial community structure of medicinal plants. However, few studies on the endophytic bacteria in P. notoginseng, particularly in dry P. notoginseng roots as a raw medicinal material, have been conducted. In this study, fresh P. notoginseng and dry P. notoginseng were analysed using high-throughput sequencing on an Illumina MiSeq platform to explore the diversity and functions of the endophytic bacteria in different parts of P. notoginseng. The results showed that a total of 201 operational taxonomic units were obtained from fresh P. notoginseng and dry P. notoginseng. The dominant phyla in the fresh and dry P. notoginseng were Proteobacteria (85.9%) and Firmicutes (99.9%), respectively, whereas the dominant genera in these samples were Enterobacter (84.4%) and Bacillus (99.6%), respectively. Fresh P. notoginseng exhibited a higher degree of endophytic bacterial diversity than dry P. notoginseng, but functional prediction of metabolism indicated that the relative abundance of the metabolic function of terpenoids and polyketides synthesis in the dry sample was higher than that in the fresh sample. Our study indicates significant differences in the diversity and metabolic function of the endophytic bacteria between fresh and dry P. notoginseng, providing useful information for the exploitation and utilization of endophytic bacteria resources from P. notoginseng.

Inhibitory effects of essential oils from Asteraceae plant against pathogenic fungi of Panax notoginseng

AIMS

Diseases caused by pathogenic fungi was a major constrain in increasing productivity and improving quality of Panax notoginseng. The aim of this research was to evaluate the inhibitory activity of essential oils (EOs) from Asteraceae family, Chrysanthemum indicum and Laggera pterodonta, against pathogenic fungi of P. notoginseng.

METHODS AND RESULTS

The antifungal activity was investigated using multiple methods, disclosing that the EOs from C. indicum and L. pterodonta are active against hypha growth of different fungi but with different degrees of potency. Checkerboard testing indicated that the combination of EOs with hymexazol had synergistic effect against Pythium aphanidermatum, and exhibited additive effects against bulk of targeted pathogenic fungi. Besides, we found that the baseline sensitivity of Fusarium oxysporum to L. pterodonta EOs was higher than those of C. indicum by means of mycelium growth rate method. Finally, the practicability of those EOs as plant pesticide was confirmed by in vivo model showing that EOs can significantly inhibit the occurrence of root rot of P. notoginseng caused by F. oxysporum.

CONCLUSION

Those studies suggest that the EOs from C. indicum and L. pterodonta had the potential to develop into new pollution-free pesticides for the protection of precious Chinese herbal medicines.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provided a new way of biological control for overcoming the frequent diseases occurrence of P. notoginseng.

A transcriptome analysis uncovers Panax notoginseng resistance to Fusarium solani induced by methyl jasmonate

BACKGROUND

Panax notoginseng is a famous Chinese herbal medicine, but the root rot disease mainly caused by Fusarium solani severely reduces the yield and quality of its medicinal materials.

OBJECTIVE

The defense priming in P. notoginseng through exogenous application of signaling molecule will supply theoretical support for the exogenous regulation of disease resistance in P. notoginseng.

METHODS

In this study, the exogenous application of methyl jasmonate (MeJA) increased P. notoginseng's resistance to F. solani. Furthermore, the P. notoginseng transcriptome during F. solani infection was investigated through next-generation sequencing to uncover the resistance mechanism of P. notogingseng induced by MeJA.

RESULTS

The de novo assembly of transcriptome sequences produced 80,551 unigenes, and 36,771 of these unigenes were annotated by at least one database. A differentially expressed gene analysis revealed that a large number of genes related to terpenoid backbone biosynthesis, phenylalanine metabolism, and plant-pathogen interactions were predominantly up-regulated by MeJA. Moreover, jasmonic acid (JA) biosynthesis-related genes and the JA signaling pathway genes, such as linoleate 13S-lipoxygenase, allene oxide cyclase, allene oxide synthase, TIFY, defensin, and pathogenesis-related proteins, showed increased transcriptional levels after inoculation with F. solani. Notably, according to the gene expression analysis, JA and ethylene signaling pathways may act synergistically to positively regulate the defense responses of P. notoginseng to F. solani.

CONCLUSION

JA signaling appears to play a vital role in P. notoginseng responses to F. solani infection, which will be helpful in improving the disease resistance of P. notoginseng cultivars as well as in developing an environmentally friendly biological control method for root rot disease.

Negative Plant-Soil Feedback Driven by Re-assemblage of the Rhizosphere Microbiome With the Growth of Panax notoginseng

There is a concerted understanding of the accumulation of soil pathogens as the major driving factor of negative plant-soil feedback (NPSF). However, our knowledge of the connection between plant growth, pathogen build-up and soil microbiome assemblage is limited. In this study, significant negative feedback between the soil and sanqi (Panax notoginseng) was found, which were caused by the build-up of the soil-borne pathogens Fusarium oxysporum, F. solani, and Monographella cucumerina. Soil microbiome analysis revealed that the rhizospheric fungal and bacterial communities were changed with the growth of sanqi. Deep analysis of the phylum and genus levels corroborated that rhizospheric fungal Ascomycota, including the soil-borne pathogens F. oxysporum, F. solani, and especially M. cucumerina, were significantly enriched with the growth of sanqi. However, the bacteria Firmicutes and Acidobacteria, including the genera Pseudomonas, Bacillus, Acinetobacter and Burkholderia, were significantly suppressed with the growth of sanqi. Using microbial isolation and in vitro dual culture tests, we found that most isolates derived from the suppressed bacterial genera showed strong antagonistic ability against the growth of sanqi soil-borne pathogens. Interestingly, inoculation of these suppressed isolates in consecutively cultivated soil could significantly alleviate NPSF. In summary, sanqi growth can suppress antagonistic bacteria through re-assemblage of the rhizosphere microbiome and cause the accumulation of soil-borne pathogens, eventually building negative feedback loops between the soil and plants.

Antifungal Effect of Essential Oils from Five Kinds of Rutaceae Plants - Avoiding Pesticide Residue and Resistance

Panax notoginseng root is a traditional Chinese herb, of which the yield and quality have been seriously affected by microorganisms, and is commonly used to treat various kinds of bleeding. In this experiment, the effects of the antifungal properties of essential oils (EOs) from five kinds of Rutaceae plants on the growth of three kinds of pathogens were studied to develop natural, environmentally friendly antifungal agents. Citrus medica EO was found to have stronger inhibitory effects on the growth of pathogenic fungi in vitro than other EOs with the Oxford cup method, of which the chemical composition was further investigated by GC/MS. The major components were d-limonene (22.79 %) and γ-terpinene (9.71 %). The antifungal activities were evaluated by MIC and FIC assays. In these assays, C. medica EO, d-limonene and γ-terpinene were effective against three pathogens of P. notoginseng with MIC values ranging from 0.12 to 12.05 mg/mL. The association between hymexazol and C. medica EO showed a high synergistic effect with lower FIC index values (FICi=0.31-2.00). Furthermore, C. medica EO was further assessed in P. notoginseng planted in a continuous cropping soil (CCS) and was found to reduce the disease incidence and disease severity compared with P. notoginseng planted in CCS only without EO addition. This finding suggested that C. medica EO has potential as a natural environmentally antifungal agent against pathogens of P. notoginseng, ensuring its safety.

Monitoring Antifungal Agents of Artemisia annua against Fusarium oxysporum and Fusarium solani, Associated with Panax notoginseng Root-Rot Disease

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.

The Fight Against Panax notoginseng Root-Rot Disease Using Zingiberaceae Essential Oils as Potential Weapons

The root of Panax notoginseng (P. notoginseng) is one of the most highly valuable medicinal herbs in China owing to its pronounced hemostatic and restorative properties. Despite this important fact, growing P. notoginseng is seriously limited by root-rot diseases. In studies aimed at developing a solution to this problem, environment-friendly essential oils (EOs) of five medicinal plants of the family Zingiberaceae were tested for their inhibitory effects on the growth of three main soil pathogens associated with the root-rot diseases of P. notoginseng. The results showed that the EOs of Alpinia katsumadai Hayata and Zingiber officinale Roscoe promote significant reductions in the mycelium growth of the pathogen in vitro at a concentration of 50 mg mL-1, which is much higher than that needed (5 mg mL-1) to reduce growth by the positive control, flutriafol. Furthermore, the chemical components of the two EOs were determined by using GC-MS analysis. Eucalyptol was found to account for more than 30% of the oils of the two plants, with the second major components being geranyl acetate and α-terpineol. These substances display different degrees of fungistasis in vitro. To further determine the effects of the EO of Zingiber officinale (Z. officinale) in vivo, soilless cultivation of P. notoginseng with pathogen inoculation was conducted in a greenhouse. Addition of the petroleum ether extract (approximately equal to EO) of Z. officinale to the culture matrix causes a large decrease in both the occurrence and severity of the P. notoginseng root-rot disease. The decreasing trend of net photosynthetic rate (Pn), stomatal conductance (gs), intercellular CO2 concentration (Ci), and transpiration rate (Tr) were all alleviated. In addition, the activities of catalase (CAT), peroxidase (POD), and the malondialdehyde (MDA) content were also largely reduced after pathogen infection, with the root activity being higher than that of the control. Taken together, the findings reveal that the EOs from plants might serve as promising sources of eco-friendly natural pesticides with less chemical resistance.