Studies On The Mechanism Of Continuous Cropping Obstacle Of Condonopsis Tangshen Oliv.and Its Remediation

Codonopsis tangshen Oliv.has a long history in terms of medicinal use and cultivation.However,there is a serious continuous cropping obstacle in the production of Codonopsis tangshen Oliv.,which would lead to serious problems of plant diseases and insect pests.It can result in a significant reduction in production and even no harvest,thus seriously restricting the sustainable development of related industries.At present,there are limited reports on the mechanism of continuous cropping obstacle in the production of Codonopsis tangshen Oliv.In order to solve this problem,it is necessary to clarify the mechanism of continuous cropping obstacle of Codonopsis tangshen Oliv.with research on corresponding remediation technology.To this end,a field experiment was carried out in the genuine producing area of Codonopsis tangshen Oliv.located in Banqiao Town,Enshi City.The study took continuous cropping and non-continuous cropping Codonopsis tangshen Oliv.as research objects,with high-throughput sequencing being used to investigate the dynamic changes of microbial communities in the rhizosphere soil of continuous cropping Codonopsis tangshen Oliv.And transcriptome sequencing analysis was used to identify continuous cropping stress response genes.Combined with production practice,the occurrence mechanism of continuous cropping obstacle of Codonopsis tangshen Oliv.was systematically studied and analyzed,with a discussion on the remediation effect of additionally applying p H regulator,organic fertilizer and microbial fertilizer on continuous cropping obstacle of Codonopsis tangshen Oliv.,thus providing a theoretical basis for reducing continuous cropping obstacle of Codonopsis tangshen Oliv.The majorResults are as follows:1.Continuous cropping had large barrier effect on the growth of Codonopsis tangshen Oliv.and its soil.After continuous cropping of Codonopsis tangshen Oliv.,the soil acidification was intensified and aluminum toxicity was enhanced,shown by a decrease of 0.14 units in soil p H and an increase of 0.81cmol/kg in the exchangeable aluminum content of the soil;The contents of soil organic matter,alkali-hydrolyzable nitrogen,rapid available phosphorus and potassium decreased significantly;the quantity and proportion of soil bacteria and actinomycetes decreased while that of fungi increased;the growth of plants was severely inhibited,the yield of fresh medicinal materials was significantly reduced,and the accumulation of polysaccharides and lobetyolin in Codonopsis tangshen Oliv.was significantly reduced.2.The disturbance of rhizosphere microflora in the continuous cropping area of Codonopsis tangshen Oliv.was closely related to the continuous cropping obstacle.It was found that continuous cropping of Codonopsis tangshen Oliv.resulted in a significant decrease in the relative abundance of beneficial bacteria in soil,including Planctomycetes,Nitrospirae,chloroflexi and Latescibacteria.On the contrary,the number of potential pathogenic bacteria including Acidobacteria,Saccharibacteria,Parcubacteria and Elusimicrobia had accumulated along with continuous cropping.The continuous cropping of Codonopsis tangshen Oliv.could lead to the increase in the contents of Candidatus Solibacter,Rhodanobacter,Gemmatimonas and Nitrobacter in soil,while the contents of Nitrospira,H16,Variibacter and Haliangium would obviously decrease.The continuous cropping of Codonopsis tangshen Oliv.could result in the accumulation of several potential pathogenic bacteria including fungal pathogens,e.g.,Ceratobasidium,Bullera,Monographella,Candida,etc.The continuous cropping of Codonopsis tangshen Oliv.caused the reduction of beneficial microorganisms and accumulation of pathogenic microorganisms in soil.Meanwhile,by tracking the variation trend of the soil's physical and chemical properties,correlation analysis showed that the variation coupling of soil microorganism groups and the physical and chemical properties of soil under continuous cropping of Codonopsis tangshen Oliv.contributed to the occurrence of continuous cropping obstacle.3.The aquatic extract from rhizosphere soil of continuous cropping Codonopsis tangshen Oliv.had allelopathic inhibition on seed germination and seedling growth.The effect of aquatic extract from rhizosphere soil of continuous cropping Codonopsis tangshen Oliv.on seed germination was studied in this paper.It was found that when the concentration of the extract reached 50mg/m L,inhibitory effect was shown on the seed germination index of Codonopsis tangshen Oliv.Even low concentration of the extract could significantly inhibit the embryo length,seedling fresh weight and seedling vitality index of Codonopsis tangshen Oliv.Various concentrations of rhizosphere soil extract showed inhibitory effects on the activities of SOD and POD antioxidant enzymes in seedlings,and the activities of enzymes were significantly reduced compared with the control group,but there was no significant effect on MDA.The soil extract of continuous cropping Codonopsis tangshen Oliv.inhibited the germination of Codonopsis tangshen Oliv.seeds,which confirmed the autotoxicity of Codonopsis tangshen Oliv.4.Candidate genes responding to continuous cropping obstacle stress of Codonopsis tangshen Oliv.were identified through transcriptome sequencing of the leaves of Codonopsis tangshen Oliv.in the continuous cropping area.It was found that the Chlorophyll a,Chlorophyll b and total chlorophyll content decreased in the leaves of Codonopsis tangshen Oliv.in the continuous cropping area.In addition,plants grown under C-cro condition exhibited significantly higher MDA content and CAT activity,but markedly lower SOD activity than plants grown under NC-cro.In order to further clarify the molecular mechanism behind the continuous cropping obstacle of Codonopsis tangshen Oliv.,RNA-Seq technology was used to represent the transcriptome of Codonopsis tangshen Oliv.leaves responding to continuous cropping treatment.In general,total RNA from the continuous cropping group(c-cro)and the non-continuous cropping control group(nc-cro,control)were used to construct 6 c DNA libraries.After clipping and filtering the original sequence,a total of 176 million and 187million clean reads were generated from the c-cro group and the nc-cro group,respectively.These reads were then assembled into 196,814 genes.A total of 762differentially expressed genes(DEGs)were detected between the two groups(430up-regulated expressions and 332 down-regulated expressions).Pathway enrichment analysis showed that DEGs was mainly involved in tyrosine degradation,phenylalanine and tyrosine catabolism,tyrosine metabolism,glycogen synthesis,amino sugar and nucleotide sugar metabolism as well as GPCR signals.These screened differential gene expression patterns were consistent with q PCR verification results.Candidate genes(psb A?psb W?MYC2?PR-1,etc.)responding to continuous cropping obstacle stress of Codonopsis tangshen Oliv.were identified in this study.The results are helpful to explore the molecular mechanism of continuous cropping obstacles of C.tangshen and provide a basis for its final solution.5.Comprehensive measures such as improving soil environment to remedy the continuous cropping obstacle of Codonopsis tangshen Oliv.can significantly increase yield and enhance quality.The test results show that,quicklime and calcium magnesium phosphate fertilizer had remarkable effects on improving the soil of continuous cropping Codonopsis tangshen Oliv.Their suitable application rates for improving acidified soil of Codonopsis tangshen Oliv.(p H 4.12;soil volume of 1.15 g·cm^-3;tillage layer thickness of 15cm)were 1.73-3.45 t·hm^-2and 3.45-6.90 t·hm^-2respectively.After the soil was treated,it could achieve the suitable soil p H(5.5?6.5)for the growth of Codonopsis tangshen Oliv.seedlings,and the fresh weight of Codonopsis tangshen Oliv.roots could be increased by40.5%-78.5%and 28.4%-78.8%respectively.Organic fertilizer,silicon calcium potassium magnesium fertilizer and microbial fertilizer also had good abatement effects.Compared with the control group,the treatment through organic fertilizer(4500 kg/hm²)could significantly increase the yield of Codonopsis tangshen Oliv.by 20.2%,and it significantly increased the polysaccharide content of Codonopsis tangshen Oliv.by18.2%.The treatment through silicon calcium potassium magnesium fertilizer(750kg/hm²)could significantly increase the yield of Codonopsis tangshen Oliv.by 13.8%,while the polysaccharide and lobetyolin content of Codonopsis tangshen Oliv.had no significant difference compared with the control group.Although microbial fertilizer(750kg/hm²)did not significantly promote the yield,it could significantly increase the polysaccharide and lobetyolin content of Codonopsis tangshen Oliv.by 12.2%and 18.3%respectively.Based on the above study,a preliminary attempt was made to construct a technical system for reducing the continuous cropping obstacle of Codonopsis tangshen Oliv.