Study On Restoration Of Rhizosphere Microecology Of Phytophthora Disease By Paenibacillus Polymyxa LRS-1

Phytophthora diease is a worldwide soil-borne disease which seriously threatens the production of pepper.It can lead to serious loss of yield and quality of pepper under field or facility cultivation conditions.Biological control of Phytophthora capsici has the advantages of high efficiency,pollution-free and sustainable.In this study,Phytophthora capsici diseased soil was taken as the research object,and the excellent Biocontrol Strain LRS-1(Paenibacillus polymyxa,published)was used as biocontrol material.Based on the methods of GC-MS,high-throughput sequencing and bioinformatics analysis,the microecological regulation mechanism of P.polymyxa LRS-1 in Phytophthora capsici diseased soil in the interaction process of "pathogen biocontrol bacteria indigenous microorganism" system was studied,in order to provide the necessary reference for the rhizosphere soil quality remediation of crop disease barriers.The main conclusions are as follows:1.Inoculation of P.polymyxa LRS-1 could not only control Phytophthora disease,but also significantly improve the negative stress effect of Phytophthora capsici on pepper root allelopathy.The results of root exudates analysis showed that the concentrations of organic acids,protein and soluble sugar in Pepper Root Exudates of Phytophthora infestans positive control(PC)were significantly increased compared with disease-free negative control(CK).Inoculation of P.polymyxa LRS-1 could significantly reduce the concentrations of organic acids and soluble sugar,and significantly increase the protein level.The results of GC-MS showed that there were many compounds in pepper root exudates,among which esters,acids and amines with relatively complex structures were more,and hydrocarbons and alcohols with linear or branched alkanes were less;Under the stress of Phytophthora capsici,the kinds of compounds in pepper root exudates increased significantly,such as methyl palmitate,1,2,3,5-tetramethylbenzene,2-ethylhexanol,2,6-di-tert-butyl-p-cresol,ethyllinoleate,malic acid,2,6-di-tert-butyl-p-cresol were detected,3-dimethylnaphthalene,β-sitosterol and other specific compounds,but inoculated with P.polymyxa LRS-1 was beneficial to pepper root compound species and content under Phytophthora disease stress,which tended to be consistent with CK;The relative content of 3-phenyl-2-methyl acrylate and other compounds in root exudates of pepper inoculated with LRS1 was the highest,which was significantly higher than that of CK and PC.2.After inoculating with P.polymyxa LRS-1,the bacterial community structure of rhizosphere soil with Phytophthora capsici disease barrier was well repaired.The results of alpha diversity analysis showed that the richness index and diversity index of CK were the highest,while the results of four diversity indexes showed PC < LRS1 < CK in each treatment.Venn analysis showed that CK and LRS1 had 837 OTUs,961 and 921 OTUs,respectively.The species composition of CK and LRS1 was similar and highly overlapped,which was significantly higher than that of PC treatment.At phylum level,the dominant species of each treatment were Proteobacteria,Firmicutes and Actinobacteria,with an average rate of 36.35%,15.28% and 15.21%,respectively.It can be said that these three phyla were less affected by Phytophthora disease;In terms of genus level,the number of bacterial species with abundance more than 1% in rhizosphere soil of CK,LRS1 and PC treatments were 19,20 and 17,respectively.Paenibacillus species were inoculated with P.polymyxa LRS-1,and accounted for 0.98% of the total in LRS1 treatment.PCA principal component analysis showed that there were significant differences in rhizosphere soil bacteria among the treatments.3.Inoculation of P.polymyxa LRS-1 was beneficial to the restoration and reconstruction of bacterial interaction network in rhizosphere soil.The results of rhizosphere bacterial interaction network analysis showed that LRS1 interacted with PC and CK,and the interaction level between LRS1 and CK was more close.The results of topology index analysis show that the total number of all the generic nodes in different processing is 725,and 425 genera are shared.The generic nodes of CK,LRS1 and PC are 253,252 and 220 respectively.From the perspective of network heterogeneity,the heterogeneity of CK-PC network is higher than that of CK-LRS1 network.The results of core species analysis showed that a total of 6 genera,such as Massilia,Microvirga,Bacillus,Tepidisphaeraceae,Chitinophagaceae and Flaviolibacter,played a key role in the maintenance of rhizospheric bacterial microecological interaction network,and the inoculation of P.polymyxa made the greatest contribution to the interaction among species Microvirga,Tepidisphaeraceae and Chitinophagaceae.