Effects Of Five Pesticides On Microbial Community Structure And Function In Cultivation Soil Of Panax Notoginseng

Panax notoginseng has great economic and medicinal value,but its development is seriously restricted by continuous cropping obstacles and diseases.In this paper,the combination of culture-independent pure culture approachs is used to investigate the affect of five commonly fungicides on the compositions and functions of bacterial and fungal communities,and the relationship between microorganism and disease of Panax notoginseng.The analysis of data by high-throughput sequencing indicate that there are no significant differences on the microbial diversity in the soil samples of Panax notoginseng treated by 5 fungicides,but the microbial community compositions and structures are changed to different degrees.The effects of thiophanate-methyl/thiram(TM.thiram),iprodione and polyoxins on the microbial community in the soil are greater than that of procymidone and mancozeb.For fungal communities,the application of procymidone can increase the relative abundance of Mortierella in the soil.But the application of iprodione,polyoxins and TM.thiram can reduce the relative abundance of Basidiomycota and Mortierella in the soil.All five fungicides increased the abundance of Trichoderma in the soil to varying degrees.For bacterial communities,the application of mancozeb can increase the abundance of Proteobacteria in the soil,while procymidone,iprodione and TM.thiram can reduce the abundance of Acidobacteria in the soil.All five fungicides increased the abundance of Actinobacteria in the soil.The function prediction analyses show that polyoxins and TM.thiram can significantly reduce the abundance of phytopathogenic fungi in soil of Panax notoginseng.The enzyme abundance related to the life activities of fungi decreased significantly after the application of pesticides,and the enzyme activity are most affected by TM.thiram.However,the abundances of all the functional gene of bacteria increased to different degrees in soil treated by 5 fungicides compared with the control.Three hundred and six fungal isolates obtained from soil samples belong to 4 families,7 classes,19 orders,32 families and 45 genera.Fusarium,Trichoderma and Clonostachys are the dominant genera.The samples in the iprodione treatment had the most number of isolated fungi and the highest species diversity.The number of fungi from soil treated by the mancozeb decreased sharply.Eighteen fungal strains showed the activities against at least one of Fusarium oxysporum,Fusarium solani,Plectosaphaerella cucumerina and Alternaria Panax.Eight fungi with the strongest antagonism and four pathogenic fungi causing root rot of Panax notoginseng were selected to investigate the effects of five fungicides on their morphological characteristics and growth rate.Mancozeb and TM.thiram has a broad spectrum of antibacterial action and extremely significant inhibitory effect.Polyoxins shows a maximum growth inhibition rate of only 52% at a concentration of 200 mg/L.Fungicides caused the significant changes in the morphological characteristics of fungi including the mycelium curled and bent,the ability of colony diffusion growth is weakened and irregular growth,color change of soluble pigment.