| China is the second largest banana producer,however,banana production has been seriously threatened by Fusaruim wilt disease,which is also known as Panama disease and caused by Fusarium oxysporum f.sp.cubense race 4(Foc 4).Our previous work reported that there was a field which has been mono-cropped banana for many years,but the incidence of Fusarium wilt remained a low level showing a natural suppressiveness to Fusarium wilt disease in the main banana growing areas of Hainan.Based on this,in this present study soil and different banana plant tissues(root,stem and leaf)samples from the disease suppressive and co-located disease conductive banana orchards were collected to screen,isolate,identify and compare the composition and function of culturable bacterial and Pseudomonas composition using traditional dilution counting method and 16S rRNA PCR technology.Further high-throughput sequencing was also conducted to explore the characteristics of soil and endophytics in these samples.Lastly the differences of soil metabolic components were also studied by Gas Chromatography Time-of-Flight Mass Spectrometry(GS-TOF-MS)to explore the metabolic characteristics of disease suppressive soils.The aim of this study was to reveal the microbial ecological mechanism of disease suppressive soil from three aspects:the composition and function of culturable bacteria of endophytic bacterial community in different parts of banana,the composition of total bacterial community and soil metabolic components.The main results are as follows:1.A total of 766 strains of culturable bacteria were isolated from banana soil,rhizosphere and different tissues,identified and preserved,belonging to Actinomycetes,Bacteroides,Firmicutes and Proteobacteria.There were significant differences in the composition of bacteria in soil and different tissues.Compared with the disease conductive banana orchards,the composition of culturable bacteria and Pseudomonas in the soil and tissues of different banana plants of the disease suppressive banana orchards has its own unique characteristics.Proteobacteria is the dominant phylum,and 10 genera,such as Sphingobacterium,Acidovorax and Herbaspirillum are endemic to disease suppressive banana orchards;among them,the relative abundance of Pseudomonas in banana orchard samples with disease suppressive was higher than that in banana orchard samples with disease conductive,which contributed greatly to the difference of biocontrol bacteria.Further isolation of Pseudomonas spp.and identification of its antagonistic ability against pathogenic showed that:the composition of culturable bacteria and Pseudomonas spp.in the soil and different tissues of banana orchards with disease suppressive type had its own uniqueness.362 strains of Pseudomonas spp.belonging to 11 species were successfully screened in banana orchards of disease suppressive type.Compared with those of disease conductive banana orchards,Pseudomonas aeruginosa,Pseudomonas fulva,Pseudomonas citronelloils,Pseudomonas plecoglossicida,Pseudomonas taiwanensis,Pseudomonas lutea and Pseudomonas rhizosphaerae were endemic,and the number of Pseudomonas biocontrol was more.2.The endophytic bacterial community of healthy banana plants from disease suppressive orchard was significant different from those from disease conducive orchards revealled by high throughput sequencing results.In total,the richness and diversity from soil samples(bulk and rhizosphere soil)was higher than those from banana tissue samples,such as root,stem and leaf.Rhizobium,Clostridium sensu stricto,Devosia,Sporolactobacillus,Herbaspirillum,Brevundimonas and Deinococcus are seven genera that are general identified in soil,rhizosphere,root,stem and leaf samples of healthy bananas.The relative abundance of Fusarium in the rhizosphere soil and roots of the disease suppressive banana orchards is lower than that of the disease conductive banana orchard.Further we also found bacterial richness was negatively correlated with the relative abundance of Fusarium.Interestingly,as it is the most widely used biocontrol agents,Pseudomonas is the most abundant bacterial genera in the rhizosphere soil and showed a negative correlation to Fusarium.3.A significant difference of metabolic characteristic between disease suppressive and conductive soil revealled by principal component analysis based on the results of soil GS-TOF-MS non-target metabonomics.The contents of the contents of amino acids,monosaccharides and putrescines in disease suppressive soil were higher while organic acids,polysaccharides,nucleic acids and methylamine were lower compared those in disease condutive soil.There are contents of 16 different compounds such as monopalmitin,monostearin,fructose,glucose,glycerol glycerol,methylamine,palmitic acid,phosphate,putrescine,stearic acid,xylose and palatinit were found in diseases suppresstive soil compared to disease conductive soils.Among these 16 compounds,five compounds namely monopalmitin,monostearin,methylamine,phosphate and xylose were significant different between disease suppressive and conducive soils.In conclusion,the composition of culturable and total bacterial community in soil and endophytic bacterial communities in different banana tissues collected from disease suppressive were significant different from those in disease conducive soil.Among these,Pseudomonas is the mostly common known biocontrol agents and contributed a large proportion to the difference for culturable bacterial composition in disease suppressive and conducive soil.And this finding was also comfirmed by high throughput sequencing since the relative abundance of Pseudomonas in disease suppressive banana orchards is significant higher than that in disease conducive orchards and displayed a negative correlation to the relative abundance of Fusarium.And there were also significant differences in the soil metabolic characteristics between disease suppressive soil and disease conductive soil as disease suppressive soils contained a higher content of amino acid,monosaccharide and putrescine. |
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