Relationship Between Three Tobacco Diseases And The Microbial Communities In Soil Under Different Farming System And Phyllosphere

Tobacco soil born disease and leaf disease are closely related to the microbial communities in soils and on leaves,however,most previous studies were focused on selection and application of single antagonistic strains from soil or leaves.Comprehensive understanding on the relationship between the microbial communities in soils and on leaves and the main tobacco diseases is still lack.Expanding our knowledge on this aspect could provide theoretical and applicable value for obtaining effective biocontrol flora,reducing the agriculture chemicals and environmental protection.The present study focused on the relationship between three main tobacco diseases,including bacterial wilt disease,black shrank disease and wildfire disease and the microbial communities in soils and on leaves.Main findings are as follows:(1)Soil bacterial communities in 15 tobacco cropping fields were analyzed through 16 s rDNA high-through put sequencing approach,and the microbial communities were then related to the tobacco bacterial wilt disease.The results indicated that soil microbial diversity had a strong effect on plant disease outbreak,with diversity and rate of wilt disease showing an inverse relationship;and soils with similar microbial community composition have similar disease infection rate,i.e.when the soil had similar composition with ‘healthy' group that with plant-beneficial microbes maintained the below-ground ecosystem stability,the soil might tend to be disease-suppressive(2)The molecular ecological network analysis based on random matrix theory showed that a more complex network with more ecological niches might be beneficial for tobacco wilt suppression.We concluded that microbial community in disease-suppressive soils may be consisted with high diversity,consistent composition with plant-beneficial microbes as the important component and complex network with more ecology niches.(3)The ITS high-through put sequencing was carried out to investigate the soil fungal communities during winter fallow(WF)and summer growing(SG)stage.The results showed that compared with continuous cropping,rotation tobacco with maize,turnip and lily reduced tobacco black shrank disease effectively.WF soil had more fungal OTUs than the SG soil(t-test,p < 0.001),and the fungal community diversity was significantly(t-test,p < 0.001)higher during WF stage than SG stage.However,the fungal community diversity didn't show obvious differences between rotation regimes.(4)WF and SG fungal communities differed significantly in fungal community composition(ANOSIM R=0.914,p = 0.001),the fungal community composition also differed obviously among rotation regimes.The shift in community composition was largely attributable to the presence of a small portion of Dothideomycetes in WF stage which dominates SG stage.CCA and Mantel analyses indicated the soil temperature and organic matter were responsible for the variation in fungal community composition.The phylogenetic diversity analysis indicated that WF fungal community had a higher phylogenetic diversity than SG fungal community(t-test,p < 0.001).The results indicated that the fungal community showed obvious seasonal succession.(5)The ‘Null-mode” were used to reveal the ecological reason for fungal seasonal succession.When the dispersal limitation dominated the fungal community assembly during the WF stage,homogenizing dispersal was the main assembly process in SF stage.Thus,the ecological processes might be responsible for the differences in fungal communities between SG and WF stage,therefore,responsible for the tobacco black shrank disease outbreak.Therefore,improve of soil fungal community would be very helpful for controlling plant fungal disease.(6)We obtained three excellent antagonistic bacteria inoculums(namely inoculum A,B and C)from tobacco phyllosphere environment,and then applied them to the tobacco plants to study the effects of inoculation of antagonistic inoculum on phyllosphere microbial communities and the microbial interactions.The results showed that all three bacteria inoculums inhibited tobacco wildfire disease effectively(ANOVA,p < 0.05).The high-through put sequencing approach showed that the dominant bacterial in A,B and C inoculum were Actinobacteria,Bacilli,and Gammaproteobacteria,respectively.After applied in the tobacco leaves,the B and C inoculum had better colonization ability than inoculum A.The relative abundance of the three dominant populations correlated negatively with wilt disease infection rate,indicating all three inoculums had good biocontrol effects.Community diversity analysis indicated that application of three inoculums increased leave bacterial community significantly.Community composition analysis indicated inoculum B and C changed tobacco leaf bacterial community composition obviously,whereas inoculum A didn't.The molecular ecology network analysis showed that after inoculation of inoculums the interaction between bacteria on leaves became more complicated,indicating that the antagonistic bacteria could enhance the interactions among bacteria on leaves to inhibit tobacco wildfire disease.The results offer theoretical evidences for application of biological agents.