| Silicon(Si) is the second most abundant mineral element in soil and comprises~28% of earth’s crust, the beneficial role effects of this elements in conferring plant growth, development,resistance to both abiotic and biotic stresses have been well documented in many plant species and has received increasing attention. In this regard, many researchers have carried out for Si improved crop resistance mechanism of launched a series of studies, Previous solution culture was used to study showed that silicon by increasing the activity of Cucumber(Cucumis sativas L.) in plant disease resistance related enzymes reduce the incidence of Fusarium wilt, caused by the soil-borne pathogen Fusarium oxysporum f. sp. cucumerinum Owen(FOC), is a serious vascular disease worldwide. However, it is not clear whether Si can enhance the resistance of cucumber to Fusarium wilt by changing the soil microbial community.In this experiment, we studied the effects of soil, with cucumber soil and foliar application of Si on cucumber seedling growth and disease indexes Fusarium wilt of cucumber seedling, and rhizosphere soil microbial communities structure, abundance and composition were analyzed by molecular methods such as PCR-DGGE, qPCR, Miseq; then, the feedback effects of rhizosphere soil biota on cucumber seedling Fusarium wilt resistance was assessed, The aim was to study the role of soil microorganisms by changed Si in improving the resistance to Fusarium Wilt of cucumber seedlings. Furthermore, in vitro experiments were made to study the effect of Si on the growth of FOC and streptomyces DHV3-2 in sterilized soil. The aim was to determine whether soil application of Si can directly inhibited the growth of FOC. Further clear Si-mediated cucumber seedling resistance against FOC through change of soil microbial community mechanism of action,to explain from the Angle of the soil ecological environment silicon crop disease resistance mechanism to provide theoretical basis. The main results were as follows:(1) With cucumber soil and foliar application of Si significantly increased the fresh and dry weight of cucumber seedling after 20 days application of Si treatment; In addition, with cucumber soil application of Si decreased the incidence of Fusarium wlit of cucumber seedling, however,foliar application of Si have no effect on it. These suggested that foliar application of Si could not increase the resistance of cucumber seedling to Fusarium wilt.(2) PCR-DGGE and qPCR results showed that, soil application of Si increased the diversity indices and abundance of bacterial and fungal community; with cucumber soil application of Si increased the diversity indices and abundance of bacterial community and decreased the diversity indices and abundance of fungal community; foliar application of Si has no effect on diversity indices and abundance of bacterial and fungal community. These indicating that soil, withcucumber soil and foliar application of Si have different effect on structure and abundance of soli microbial community.(3) Miseq sequencing results showed that soil application of Si, with cucumber soil and foliar application of Si have no effect on richness index, diversitly index and composition of soil bacterial community. All 17015 OTU points belong to the 40 phylum of the bacterical, including the main phylum of Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, Bacteridetes,Gemmatimonadetes, Planctomycetes, Firmicutes; However, the soil fungal community richness index, diversity index and composition were changed, All 17015 OTU points belong to the 8phylum of the fungal, including the main phylum of Ascomycota, Zygomycota, Basidiomycota.Soil application of Si decreased the abundance of Zygomycota, Zygomycetes, Dothideomycetes,increased the abundance of Ascomycota, Basidiomycota, Fusarium, Tremellomycetes; with cucumber soil application of Si decreased the abundance of Sordariomycetes and increased the abundance of Basidiomycota, Discomycetes, Fusarium; foliar application of Si decreased the abundance of Zygomycetes, Basidiomycota, Sordariomycetes, increased the abundance of Asycomycota, discomycetes, Dothideomycetes and Phoma.(4) The principal axis(PCoA) and nonlinear multidimensional scaling(NMDS) analysis showed that the soil bacterial and fungal community structure was changed by different application of Si style. For bacterial community structure, between the with cucumber soil and folair application of Si treatment range were closer, but both of them were distance between soil applications of Si treatment. These suggested that with cucumber soil and folair application of Si were larger differences in bacterial community structure with soil application of Si; For fungal community structure, soil application of Si, with cucumber soil and foliar application of Si are far distance, showed that the difference of the community structure of fungal with the different application of Si style.(5) ANOSIM similarity analysis showed that the different application of silicon style on soil bacterial communities(R=-0.068, P=0.664) and fungal communities(R=1, P=0.001), which showed significant differences in the fungal community structure among different treatments;Different application of Si style at class level of common and unique OTU results showed, for bacterial community composition, at the class level, Acidobacteria, Actinobacteria, β-proteobacteria, α- Proteobacteria, γ-Proteobacteria were commoun for different application of Si treatment, soil application of Si was unique class Verrucomicrobia, Tenericutes. BD1-5_norank,with cucumber soil application of Si unique class was Caldisericia, foliar application of Si unique class were actinobacteria_unclassified, VadinHA17, Bacteroides; for fungal community composition Sordaromycetes, Zygomcota_incertae_sedis were commoun for different application of Si treatment, soil application of Si was unique class Ascomycetes, with cucumber soil application of Si unique class was Archacorhizomycetes, foliar application of Si unique class was Blastocladiomycetes.(6) Plant-soil feedback experiments results showed that inoculation with 6% cucumber rhizosphere soil biota from with cucumber soil application of Si into sterilized background soil treatment the Fusarium wilt disease index was significantly lower and cucumber plant root enzyme actives significantly higher in SOD, PAL and GLU after inoculation FOC; However, inoculation with 6% cucumber rhizosphere soil biota from soil and foliar application of Si into sterilized background soil treatment have on effect on the Fusarium wilt disease index and cucumber plant root enzyme actives in SOD, PAL and GLU after inoculation FOC. These suggested that cucumber rhizosphere soil biota from with cucumber soil application of Si, but not soil and foliar application,enhanced cucumber Fusarium wilt resistance.(7) In vitro results showed that Si(Si addition but didn’t adjust to pH) significantly decreased the number of FOC and streptomyces DHV3-2 spore and AdSi(Si addition and adjust to pH)significantly decreased the number of FOC and streptomyces DHV3-2 spore compared with Si0 treatment. These indicated that increase in pH is responsible for the inhibition of the growth of pathogenic fungi and benefit microbial by soluble Si in vitro. Fusaric acid production of FOC result showed that Si(Si addition but didn’t adjust to pH) and AdSi(Si addition and adjust to pH)decreased production of fusaric acid. In sterilized soil, Si had no effect on the population of FOC Therefore, Si may do not decrease cucumber Fusarium wilt disease through directly inhibit FOC in soil environment.Overall, soli, with cucumber soil and foliar application of Si have different effect on structure,abundance and composition of soil bacterial and fungal communities; with cucumber soil application of Si increased cucumber seedling resistance to Fusarium wilt by changing rhizosphere soil microbial community rather than directly inhibiting the growth of FOC. |
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