Investigation Of The Mechanism For Differences In Root Rot Occurrence Of Wild-Simulated Astragalus Membranaceus Var. Mongholicus In Hunyuan And Yingxian,Shanxi Province

The Astragali Radix is a commonly used bulk medicinal herb and Astragalus membranaceus var.mongholicus（AMM）is the mainstream cultivars in the market.Hunyuan County and Yingxian County,Shanxi province,two major production areas of wild-simulated AMM,have been suffering increasingly serious occurrence of AMM root rot year by year,but the occurrence patterns in the two areas are obviously different.In Hunyuan County,the incidence of root rot shows a trend firstly rising then decreasing with the extension of the planting years,while Ying xian County always keeps rising year by year.Research shows that there were complex interactions among"soil physicochemical properties-microbial community-pathogens",and they together affected the occurrence of soil-borne diseases.In this study,we explored the microecological mechanism of regional differences in the occurrence of AMM root rot in Shanxi Province based on the pathogen abundance,soil physicochemical properties and microbial community.The study aimed to provide the theoretical basis for the prevention and control of AMM root rot using regulation technology to the soil microbiological.The main research results are as follows:1.The abundance of pathogens were determined by real-time fluorescence quantitative PCR,and diseased and healthy soils of 4,5 and 6-year-old AMM in Hunyuan and Yingxian County were used as objects,and unplanted soils were controls.The results showed that the differences of pathogens abundance and the change patterns in the two regions were basically consistent with the occurrence patterns of root rot.The change of pathogen abundance was one of the reasons leading to the regional differences in root rot occurrence.2.Soil physicochemical properties were determined by conventional methods,and the diseased and healthy soils of 4-year-old AMM in Hunyuan and Yingxian County were used as objects,and unplanted soils were controls.The results showed that there were differences in the physicochemical properties of the soils in the two areas,and the physicochemical properties of the soils in Hunyuan County were more affected by the planting of AMM,while Yingxian County’s were more affected by the onset or otherwise of the disease.The change of soil p H,organic matter,alkali-hydrolyzed nitrogen,Cu²⁺,Zn²⁺,Mg²⁺,and Ca²⁺contents was one of the reasons leading to the regional differences in root rot occurrence.3.Based on the 16S rDNA high-throughput sequencing technology,analyses were made of the bacterial community characteristics of both the diseased and healthy soil from the root zone of 4-year-old AMM,with the soil sample from fields where AMM has never been planted as control.Alpha diversity index analysis showed that there was no significant difference in bacterial community diversity between the soils from different region,which has never been planted AMM,and the effect of AMM planting on bacterial diversity of soil from Hunyuan County was more obvious than that from Yingxian County.The occurrence of root rot in Hunyuan County was associated with higher diversity of bacteria species,while there was no associated with diversity changes in Yingxian County.The results of PCA analysis,PLS-DA analysis,and sample clustering analysis showed that there were significant differences between the bacterial community structure of soil never used for planting AMM from the different region.The bacterial community of soil from Hunyuan County was been affected more significantly by AMM planting than that from Yingxian County;and they have the trend of shifting back toward the bacterial community of soil never used for planting AMM with the occurrence of disease.The more significant changes of bacterial community which were caused by the root rot occurrence,were observed in soil from Yingxian County.The results of T-test on the relative abundance of species common in the soils from both the two regions showed that the different pattern of abundance changes including Actinomycetes and Gemmatimonadetesat et al.on the phylum level and Arthrobacter,Sphingomonas,Gemmatimonas et al.on the genus level were the key factors leading to the regional differences of root rot occurrence.The results of LEf Se differential species analysis also revealed that the characteristic bacterial populations were different in number and species,and they contributed significantly to the differences among groups of soils samples from the two regions.4.Based on the ITS high-throughput sequencing technology,analyses were made of the fungal community characteristics of both the diseased and healthy soil from the root zone of 4-year-old AMM,with the soil sample from fields where AMM has never been planted as control.Alpha diversity index analysis showed that there was significant difference in fungal community diversity between the soils from different region,which has never been planted AMM,and the effect of AMM planting on fungal diversity of soil from Hunyuan County was more obvious than that from Yingxian County.The occurrence of root rot in Yingxian County was associated with lower diversity of fungi species,while there was no associated with diversity changes in Hunyuan County.The results of PCA analysis,PLS-DA analysis showed that there were significant differences between the fungal community structure of soil never used for planting AMM from the different region.The fungal community of soil from Hunyuan County was been affected more significantly by AMM planting than that from Yingxian County.The more significant changes of fungal community which were caused by the root rot occurrence,were observed in soil from Yingxian County.The results of T-test on the relative abundance of species common in the soils from both the two regions showed that the different pattern of abundance changes including Ascomycetes and Mortierellomycota et al.on the phylum level and Trichoderma,Fusarium and Gibberella et al.on the genus level were the key factors leading to the regional differences of root rot occurrence.The results of LEf Se differential species analysis also revealed that the characteristic fungal populations were different in number and species,and they contributed significantly to the differences among groups of soils samples from the two regions.5.Correlation analysis found closer correlation existed between the soil properties and total/single pathogenic fungal abundance,between bacterial community composition and total/single pathogenic fungal abundance,and between fungal community composition and the F.solani abundance in Yingxian County than in Hunyuan County.Whereas,closer correlation existed between the soil properties and either bacterial or fungal community composition,and between fungal community composition and the abundance of the total pathogenic fungal,of F.acuminatum,and of F.oxysporum respectively in Hunyuan County than in Yingxian County.