Rhizosphere Exudate-mediated Synergistic Harm of Soil Microorganisms to Medicinal Plants in Continuous Cropping / 中国实验方剂学杂志

Continuous cropping obstacle is the bottleneck of medicinal plant cultivation, which seriously affects the quality and yield of medicinal materials. The research on the mechanism of continuous cropping obstacle has evolved from soil physical and chemical properties and allelopathy in the 1970s to the changes of rhizosphere microenvironment and plant response mechanism at present. According to the available studies in this field and our previous research work, we systematically analyzed the mechanism of rhizosphere exudate-mediated microbial community reconstruction in the soil of the medicinal plants in continuous cropping. Specifically, rhizosphere exudates, providing the carbon source and energy for microbial growth, act as inducers or repellents to induce microbial growth or transfer, thereby changing the physicochemical properties (such as acidity) of rhizosphere soil and further altering the structure of rhizosphere microbial community. Further, we comprehensively discussed the ways of synergism between rhizosphere exudates and soil microorganisms in causing harm to the medicinal plants in continuous cropping. That is, rhizosphere exudates mediate the infection of the rhizosphere by pathogenic microorganisms, increase the susceptibility of the nearby plants, inhibit the defense of the host plants, and protect the pathogens to occupy the dominant niche. The synergistic interaction results in the release of more pathogenic factors such as mycotoxins by rhizosphere pathogens, enhanced toxicity of rhizosphere allelochemicals, and deterioration of soil physical and chemical properties. This paper summarizes the role of interaction between rhizosphere exudates and soil microorganisms in the formation of continuous cropping obstacles, aiming to provide a new research idea for revealing the formation mechanism as well as the theoretical support for overcoming continuous cropping obstacles of medicinal plants.

Correlation analysis between continuous cropping obstacle of Gastrodia elata and Ilyonectria fungi and relieving strategy / 中国中药杂志

The continuous cropping obstacle of Gastrodia elata is outstanding, but its mechanism is still unclear. In this study, microbial changes in soils after G. elata planting were investigated to explore the mechanism correlated with continuous cropping obstacle. The changes of species and abundance of fungi and bacteria in soils planted with G. elata after 1, 2, and 3 years were compared. The pathogenic fungi that might cause continuous cropping diseases of G. elata were isolated. Finally, the prevention and control measures of soil-borne fungal diseases of G. elata were investigated with the rotation planting pattern of "G. elata-Phallus impudicus". The results showed that G. elata planting resulted in the decrease in bacterial and fungal community stability and the increase in harmful fungus species and abundance in soils. This change was most obvious in the second year after G. elata planting, and the soil microbial community structure could not return to the normal level even if it was left idle for another two years. After G. elata planting in soils, the most significant change was observed in Ilyonectria cyclaminicola. The richness of the Ilyonectria fungus in soils was significantly positively correlated with the incidence of G. elata diseases. When I. cyclaminicola was inoculated in the sterile soil, the rot rate of G. elata was also significantly increased. After planting one crop of G. elata and one to three crops of P. impudicus, the fungus community structure in soils gradually recovered, and the abundance of I. cyclaminicola decreased year by year. Furthermore, the disease rate of G. elata decreased. The results showed that the cultivation of G. elata made the Ilyonectria fungi the dominant flora in soils, and I. cyclaminicola served as the main pathogen of continuous cropping diseases of G. elata, which could be reduced by rotation planting with P. impudicus.

Effects of chloropicrin fumigation on soil and growth and development of Panax notoginseng / 中国中药杂志

The continuous cropping obstacle of Panax notoginseng is serious, and effective control measures are lacking. Soil disinfection with chloropicrin(CP) has been proven to be effective in reducing the obstacles to continuous cropping of other crops. In order to ascertain the effect of CP in the continuous cropping of P. notoginseng, this paper explored the influences of CP at different treatment concentrations(0,30,40,50 kg/Mu, 1 Mu≈667 m~2) on soil macro-element nutrients, soil enzyme activity, growth and development of P. notoginseng, and the accumulation of medicinal components. The results showed that CP fumigation significantly increased the content of total nitrogen, alkali-hydrolyzable nitrogen, ammonium nitrogen, nitrate nitrogen, and available phosphorus in the soil, but it had no significant effect on potassium content. The soil protease activity showed a trend of first increasing and then decreasing with the prolonging of the treatment time. Both the soil urease and acid phosphatase activities showed a trend of first decreasing and then increasing with the prolonging of the treatment time. The higher the CP treatment concentration was, the lower the urease and acid phosphatase activities would be in the soil. The protease activity was relatively high after CP40 treatment, which was better than CP30 and CP50 treatments in promoting the nitrogen-phosphorus-potassium accumulation in P. notoginseng. The seedling survival rates after CP0, CP30, CP40, and CP50 tratments in October were 0, 65.56%, 89.44%, and 83.33%, respectively. Compared with the CP30 and CP50 treatments, CP40 treatment significantly facilitated the growth and development of P. notoginseng, the increase in fresh and dry weights, and the accumulation of root saponins. In summary, CP40 treatment accelerates the increase in soil nitrogen and phosphorus nutrients and their accumulation in P. notoginseng, elevates the seedling survival rate of P. notoginseng, enhances the growth and development of P. notoginseng, and promotes the accumulation of medicinal components. CP40 treatment is therefore recommended in production.

Influences of Natural Fibrous Root Decay on Growth and Active Component Content of Paris polyphylla var. yunnanensis / 中国实验方剂学杂志

Objective:To explore the effect of natural decay of exogenously added fibrous roots on the growth and development of <italic>Paris polyphylla</italic> var. <italic>yunnanensis </italic>and its medicinal quality. Method:The effects of natural decay of fibrous roots at different amounts on mycorrhizal infection rate， physiological and biochemical indexes， and saponin contents of <italic>P. polyphylla</italic> var. <italic>yunnanensis </italic>were studied in pot culture experiments at room temperature. Result:The results showed that the infection rate of arbuscular mycorrhizal （AM） fungi in the root of <italic>P. polyphylla</italic> var. <italic>yunnanensis </italic>was not significantly affected by different fibrous root treatments， but there were significant differences in infection intensity. The photosynthetic pigment content in the leaves declined significantly with the increase in fibrous root amount， and the total chlorophyll was decreased by 78.7% at most. The contents of soluble protein， soluble sugar and malondialdehyde in the leaves of <italic>P. polyphylla</italic> var. <italic>yunnanensis </italic>showed an overall upward trend. The activities of the three protective enzymes varied. The peroxidase and malondialdehyde were reduced by 181.6% and 200.0% at most. In the root system of <italic>P. polyphylla </italic>var. <italic>yunnanensis</italic>， the contents of the above-mentioned six components decreased to varying degrees， with the largest reductions of peroxidase and malondialdehyde reaching 44.6% and 69.7%. Different fibrous root treatments resulted in a decrease in active component content of <italic>P. polyphylla </italic>var. <italic>yunnanensis</italic>. The total content of the four saponins was decreased by 58.9% at most， and the total saponin content by 46.9%. Conclusion:The natural decay of fibrous roots affects the soil microbial environment of root system， reduces the photosynthetic pigment content in leaves， and destroys the stability of cells， thus interfering with the growth and development of <italic>P. polyphylla </italic>var. <italic>yunnanensis</italic>， reducing its medicinal components， and causing continuous cropping obstacles.

Advances in research on allelopathic autotoxicity effects of medicinal plants / 中草药

Allelopathic autotoxicity is one of the important factors for the continuous cropping obstacle of medicinal plants, which will reduce the yield and quality. With the development of medicinal plants industry, the problem of continuous cropping obstacle is becoming more and more serious. How to alleviate the continuous cropping obstacle of medicinal plants needs to be solved urgently. This paper combines the research status of allelopathic autotoxicity in medicinal plants. On the one hand, expounds the mechanism that the allelochemicals of medicinal plants inhibit the growth and development of medicinal plants by damaging the cell structures, interfering with the metabolism of reactive oxygen species and phytohormones, affecting photosynthesis and so on. On the other hand, based on the analysis of the relationship between allelochemicals and continuous cropping obstacle of medicinal plants, this paper elucidated some methods to alleviate the continuous cropping obstacle of medicinal plants, such as breeding antiallelopathic autotoxicity medicinal plants varieties, rational fertilizing, selecting proper cropping system and using microbial agents, in order to provide reference for the production of medicinal plants.

Relationship between occurrence of root-rot and changes of bacterial community structure in rhizosphere soil of Panax quinquefolius / 中草药

Objective In this paper, the changes of bacterial community structure in the rhizosphere soil of healthy and root-rot Panax quinquefolius were investigated to explore the occurrence mechanism of root-rot in P. quinquefolius. Methods The changes of bacterial communities structure in uncultivated soil (group C), rhizosphere soil of 4-year-old healthy ginseng (group N), and 4-year-old root-rot ginseng (group R) were analyzed by using the Illumina MiSeq high-throughput sequencing technology. Results A total of 636 654 effective sequences and 8 422 OTUs were obtained from nine samples based on high-throughput sequencing of the 16S gene. Bacterial species detected in these samples covered 42 phyla, 106 classes, 180 orders, 158 families, and 246 genera. The main phylums were the same in the three groups, including Proteobacteria, Actinobacteria, Acidobacteria, and Chloroflexi with significantly different relative abundance. At the genera level, the composition and relative abundance of the bacterial communities in the three groups are very different. Among them, Rhodoplanes, kaistobacter, and Sphingobium may be the key bacteria causing root rot of P. quinquefolius and should be focused in the further research. Conclusion There are significant differences in the bacterial community composition from the rhizosphere soil of healthy and root-rot P. quinquefolius. This finding plays a theoretical guiding role in exploring the micro-ecological mechanism of root-rot of P. quinquefolius and improving the soil microbial community during the cultivation of P. quinquefolius.

Effect of Autotoxicity and Soil Microbes in Continuous Cropping Soil on Angelica sinensis Seedling Growth and Rhizosphere Soil Microbial Population / 中草药·英文版

Objective: To study the effect of autotoxicity and the co-effect of autotoxicity and soil microbes from continuous cropping soil on Angelica sinensis growth, root yield and content of essential oils, and soil microbal population. Methods: The pot experiments were conducted upon A. sinensis seedlings in continuous cropping soil. At the different growth stages, we determined the seedlings in growth parameters, root yield, content of essential oils, ethanol extract, and cultivable microbial populations in rhizosphere soil. Results: A. sinensis seedlings were significantly inhibited in growth, root yield and quality. Compared with the control, the composition and structure of soil microbes were changed and the diversity indexes of bacteria functional groups were reduced in rhizosphere soil of A. sinensis. A. sinensis cropping problems were more seriously after the treatment with combination of autotoxicity and soil microbes than with autotoxicity alone. Conclusions: The autotoxicity and soil microbes from continuous cropping soil of A. sinensis could cause the continuous cropping obstacle together.

Autotoxicity of water extracts from rhizosphere soil of cultivated Angelica sinensis and identification of their allelopathic compounds / 中草药

Objective: To explore the relationship between continuous cropping obstacle and autotoxicity of Angelica sinensis, autotoxic effect and organic compounds of rhizosphere soil water extract were determined. Methods: Distilled water (CK), water extract of rhizosphere soil (100, 125, 250, and 500 mg/ mL) were applied to testing their effect on early development of A. sinensis. Seed germination rate, germination index, elongation of radicle and embryo were recorded, and GC-MS was conducted for the compound identification in the extract. Results: The water extract at concentraion as low as 125 mg/mL significantly inhibited the germination and seedling growth of A. sinensis, and this inhibitory effect generally increased with the increase of the concentration of water extracts. Seventeen compounds in rhizosphere soil water extract were identified, including organic acids, ketones, aldehydes, esters, and hydrocarbons, most of them are allelophathic substance. Conclusion: Water extracts from A. sinensis rhizosphere soil have inhibitory effects on A. sinensis germination and seedling growth, and this inhibitory effect generally increased with the increases of the water extract concentration at a certain ranges. In conclusion, there is autotoxicity in continuous cropping of A. sinensis, which is one of the causes of problems associated with the continuous cropping obstacle of a single plant species.

Effects of inoculation with soil bacteria on growth of Rehmannia glutinosa in tube and potted plantlets / 中草药

Objective To investigate the cause of continuous cropping obstacle of Rehmannia glutinosa and screen beneficial bacteria.Methods In vitro cultured plantlets and potted plants were inoculated with different isolated soil bacteria. The plants were harvested and weighted in 30 and 60 d,respectively.Results In the in vitro culture experiment,11 out of 48 strains displayed promoting action on the growth of plantlets,and 11 other strains showed inhibitory or lethal action.In the potted test,16 strains showed promoting action and 13 strains showed suppressing or lethal action.Conclusion Soil bacteria influence the growth of R.glutinosa significantly.The flora of rhizosphere bacteria may be disturbed by the cultivation of R.glutinosa and inoculation of beneficial bacteria might be effective on the resolution of continuous cropping obstacle of R.glutinosa.