Metabolic Characteristic Of Tomato Rhizosphere Soil And Its Effect On The Invasion Of Ralstonia Solanacearum

In agricultural production,the outbreak of bacterial wilt can cause the broad death of tomato plants,resulting in heavy economic losses.Ralstonia solanacearum has characteristics of complex physiological races,wide range of host plant,strong ability of survival and spread and so on,which leads to poor control efficiency with commonly methods,such as chemicals application,disease resistant breeding,grafting and rotation.R.solanacearum generally colonizes plant rhizosphere in quantity before infecting host plant roots.Therefore,the interaction of R.solanacearum with rhizosphere metabolites and microbes afects the colonization of R.solanacearum.However,it is not clear how tomato rhizosphere metabolites and microbes resist the invasion of R.solanacearum.In this paper,compositions of metabolites and microbes between healthy and diseased plant rhizosphere were revealed,and effects of differential metabolites on the growth of R.solanacearum and bacterial wilt disease incidence were measured,providing theoretical basis and alternative technologies for the prevention of bacterial wilt and green production of tomatoes.The main results of this study were listed as follows:1.The gas chromatography-mass spectrometry analysis showed that tomato rhizosphere metabolites were mainly composed of organic acids,sugars,esters,alcohols,amino acids and amides.There were significant differences in compositions of two rhizosphere metabolites.The total content of rhizosphere metabolites in healthy tomatoes was significantly higher than that in diseased tomatoes,particularly,the sugar content in healthy tomato rhizosphere was significantly higher than that in diseased tomato rhizosphere.While the contents of amino acids and alcohols in healthy tomatoes rhizosphere were obviously lower than those in diseased tomato rhizosphere.Galactinol,fructose,sucrose,1,2-cyclohexanedione,myoinositol,oxamic acid,elaidic acid,melibiose,acetol,gluconic lactone and 5-aminovaleric acid were significantly enriched in healthy tomato rhizosphere.Aspartic acid,succinate semialdehyde,citramalic acid,N,N-dimethylarginine,2,3-dimethyl-succinic acid,lipoic acid,alanine,leucrose,gluconic acid,squalene,succinic acid and palmitoleic acid were significantly enriched in diseased tomato rhizosphere.2.Sucrose,fructose and melibiose enriched in healthy tomato rhizosphere were selected as carbon sources for simulated addition.The pure compounds application experiment showed that 1,10,100mmol·L^-1 of sucrose,fructose and melibiose as supplementary carbon sources separately didn’t significantly affect the growth of tcearum.Meanwhile,10mmol·L^-1 of sucrose,fructose and melibiose as sole carbon sources separately didn’t support the normal growth of R.solanacearum.The soil microbes cultivated by 10mmol·kg^-1 of sucrose,fructose and melibiose separately inhibited the growth of R.solanacearum.What’s more,adding 10mmol·kg^-1 of mixture of these three substances significantly reduced the number of R.solanacearum in soil.The results of greenhouse pot experiment showed that adding 10mmol·kg^-1 of mixture of these three substances significantly reduced the number of R.solanacearum,and increased the number of total bacteria in tomato roots,resulting in the reduction of tomato bacterial wilt incidence by 22%.3.The results from quantitative PCR showed that the number of rhizosphere total bacteria of healthy tomatoes was significantly higher than that of diseased tomatoes,while the number of rhizosphere R solanacearum of healthy tomatoes was significantly lower than that of diseased tomatoes.The results from high-throughput sequencing showed that the richness and diversity of rhizosphere bacterial community of healthy tomatoes were significantly higher than those of diseased tomatoes.Furthermore,there was significantly different of rhizosphere bacterial communities between healthy and diseased tomatoes.The relative abundance of Proteobacteria,TM7,Betaproteobacteria,Burkholderiales,Rhizobiales,Oxalobacteraceae,Rhizobiaceae,Ralstonia and Agrobacterium in healthy tomato rhizosphere were lower than those in diseased tomato rhizosphere.While the relative abundance of Bacteroidetes,Actinobacteria,Acidobacteria,Saprospirae,Actinobacteria,Gammaproteobacteria,Saprospirales,Sphingomonadales,Actinomycetales,Chitinophagaceae,Sphingomonadaceae,Micrococcaceae,Phyllobacteriaceae,Chitinophaga,Sphingobium and Phyllobacterium in healthy tomato rhizosphere was higher than those in diseased tomato rhizosphere.Differential analysis showed that differential bacterial OTUs mostly belonged to Proteobacteria,Bacteroidetes and Actinobacteria.The correlation analysis indicated that a significant correlation between the number of R.and the composition of bacterial community in tomato rhizosphere.In conclusion,compositions of both rhizosphere metabolites and microbes are significantly related to health status of tomatoes.The number of R.solanacearum was significantly correlated with diversity and composition of bacterial community in tomato rhizosphere.Sucrose,fructose and melibiose enriched in healthy tomato rhizosphere can not be utilized by R.solanacearum efficiently.Furthermore,these three substances may resist the invasion of R solanacearum by cultivating the growth of other soil microbes,so as to reduce tomato bacterial wilt incidence.