Ecological Mechanism Of Banana Fusarium Wilt Disease Suppressive Soil Resisting Fusarium Oxysporum Invasion

Soil-borne disease infected by fungal pathogens caused huge losses of many crops,including failure to growth well,yield reduction and no harvest.Among them,banana Fusarium wilt disease caused by the fungal pathogen F.oxysporum f.sp.cubense(Foc)has been severely hampered the production of banana in the world.Thus,it is essential to explore the mechanism of disease-suppressive soil against pathogen invasion.Surely this knowledge would provide a theoretical foundation for manipulating the soil microbial community to be a suppressive microbiome sustainably suppressed the wilt disease.In this thesis,we firstly confirmed that the microbiome was the key factor to suppress pathogen invasion in disease-suppressive soil,and deciphered the underlying key species involved in pathogen suppression.Addition of series-diluted soil suspensions of disease-suppressive soil to sterilized disease suppressive or conducive soil respectively assembled different soil microbiota with different diversity,and then the mechanism of assembled soil microbiome against pathogen invasion were also explored.Further,through cross inoculation of soil suspensions into sterilized disease suppressive or conducive soil,the effects of soil type(disease suppressive soil vs.disease conducive soil)and suspensions from disease suppressive or conducive soil on the assemblage of soil microbiome were studied,and the relationship between this assembled soil microbiome with the ability resisting to pathogen was also investigated.Finally,the mechanism of assembled banana rhizosphere by grown on disease suppressive or conducive soil against to the invasion of pathogen were explored.The following results are obtained:1.The microbial and ecological mechanism of disease-supprssive soil against the pathogen invasion was explored,through the microcosm experiment about inoculating Foc into sterilized or nonsterilized soil which is suppressive or conducive to banana Fusarium wilt disease.The results showed that,disease-suppressive soil can inhibit pathogen number and the suppressiveness is eliminated by steriliztion,confirming that microbiome inhibited in disease suppressive soil was the key to against pathogen invasion.Compared to disease conducive soil,a greater number of nodes,a higher number of linkages co-occurrence network was observed in disease suppressive soil.In the suppressive network,a larger proportion of negative correlations was observed between Foc and bacterial OTUs(45.45%)versus fungal OTUs(36.36%).Foc invasion exhibited significant influences on bacterial Alpha and Beta diversity.Furthermore,significant negative correlations were observed between pathogen invaded time and bacterial richness,evenness and diversity of disease conducive soil while only a significantly positive correlation between pathogen invaded time and bacterial evenness of disease suppressive soil was found.Both the Principal coordinates analysis(PCoA)and Multiple regression tree(MRT)analysis result displayed that bacterial community in disease suppressive soil responded more quickly to pathogen invasion when in comparison with disease conducive soil.And bacterial genus of Chryseolinea,Terrimonas,and Ohtaekwangia were identified as key taxa involved in disease suppression for disease suppressive soil in this study.2.The relationship between microbial diversity and the ability against pathogen invasion were also explored by addition of series-diluted soil suspensions of disease suppressive soil to sterilized disease suppressive or conducive soil respectively.The results demonstrated that microbial composition difference caused by inoculation of different series-diluted soil suspension into sterilized disease suppressive or conducive soil was firstly driven by soil type(disease conducive vs.disease suppressive soils)and then driven by different soil suspension dilution.When the microbial biomass was similar,a reduction in bacterial diversity would lead to a discrepancy in resistance ability to pathogen.Based on random forest model result,the richness of Chitinophagaceae,Cytophagaceae,Myxococcaceae,Oxalobacteraceae and the abundance of Sphingobacteriaceae were significant correlated to the resistance ability against pathogen invasion.Further,the influence of pathogen invasion on assembled micorbial community was assessed.The results exhibited that compared to the non-invaded control,no matter assembled microbiome cultivated in sterilized disease suppressive or conducive soil,the evenness in assembled microbiome increased after pathogen invasion.Meanwhile the microbial composition and structure was also significantly manipulated after pathogen invasion.Key taxa such as Massilia,which shows the ability of decomposing fungal cell walls was triggered.Moreover,microbial community with high diversity could increase the cooperation and competition relationships between distant phylogenetic species,and then increased the positive relationship proportions to maintain the stability of community to resist the invasion of pathogen based on the analysis about co-occurrence network and phylogenetic diversity.3.In chapter ?,to explore the influence of soil physi-chemical properties from disease suppressive or conducive soil on the microbial assemblage,the disease suppressive and conducive soil were mixed at different ratio and then inoculated of soil suspension from disease suppressive or conducive soil to cultivate different soil microbiome and then evaluated its ability against pathogen invasion.The result showed that when cultivated in the similar soil environment,soils inoculated with different soil suspension exhibited significant influence on the bacterial richness,beta diversity and fungal beta diversity.Except fungi in disease-suppressive soil,when the cultivated soil environment is more and more similar to original soil environment,the assembled microbiota is more and more similar to original microbiome.Furthermore,the assembled soil microbiome displayed different ability to pathogen invasion.Even the soil microbiome cultivated with soil suspension from disease conducive soil added into 100%suppressive soil(sterilized)and 80%suppressive soil plus 20%conducive soil showed a strong ability to against pathogen invasion,indicating that soil type(disease conducive vs.disease suppressive soils)plays a key role in microbiome assembly and function resisting to pathogen invasion.Moreover,Lysobacter,Sphingomonas,Streptomyces,Arthrobacter and Flavisolibacter were key taxa invloved in disease suppression.4.In chapter V,the mechanism of assembled banana rhizosphere by grown on disease suppressive or conducive soil against to the invasion of pathogen were explored under greenhouse condition.The results showed that banana grown on disease suppressive or conducive soil induced a distinct bacterial and fungal composition of rhizosphere.Compared to banana rhizosphere induced by disease conducive soil,banana rhizosphere induced by disease suppressive soil displayed an effective ability to resist the invasion of pathogen.The invasion of pathogen increased the bacteria and Foc abundance at disease conducive rhizosphere soil.The PCoA results showed Foc invasion significantly affect the bacterial and fungal community composition in disease conducive rhizosphere soil while only affect fungal community composition in disease-suppressive rhizosphere soil.For the fungal community in disease suppressive soil,Foc invasion significantly improved the abundance of Aspergillus,Talaromyces.Simplicillum,Chaetomiaceae and non-pathogenic Fusarium in the disease suppressive rhizosphere soil.For the bacterial and fungal community in disease conducive soil,Foc invasion significantly improved the relative abundance of bacterial functional groups,such as Pseudomonas,Sphingomonas,Lysinibacillus,Chryseobacterium,Chitinophaga,and fungal functional groups,such as Aspergillus,Penicillium,Simplicillum,Chaetomiaceae and non-pathogenic Fusarium.Further analysis showed that Talaromyces was unique responding taxon in disease suppressive rhizopshere soil while the relative abundance of Chaetomiaceae and non-pathogenic Fusarium was higher in disease suppressive rhizopshere compared to those in disease conducive rhizpsohere.In conclusion,microbiome exhibited in disease suppressive soil played a key role in preventing pathogen invasion.Bulk soil bacterial diversity was significantly and positively correlated the ability of pathogen invasion.Soil type(disease suppressive soil vs disease conducive soil)also involved in determining the microbiota assemblage and consequently the function against pathogen invasion.The key fungal consortia including Aspergillus,Talaromyces,Simplicillum,Chaetomiaceae non-pathogenic Fusarium in the banana rhizopshere grown by disease suppression soil effectively responded to the invasion of pathogen,and stabilized the soil microbial structure.Foc invasion improved the abundance or relative abundance of species with a potential ability to lysis of fungal cell walls.This study will provide a fundamental basic to manage soil-borne disease through manipulating soil microbiome.