| Cucumber Fusarium wilt is a vascular soil-borne disease,caused by Fusarium oxysporum f.sp.cucumerinum(FOC)and severely limited cucumber yield.The occurrence of cucumber Fusarium wilt can be exacerbated by various soil factors,including declining soil p H,deterioration of the soil microbial community,and the accumulation of soil pathogens resulti ng from continuous monocropping.Recently,chemical fungicides and soil fumigation have been criticized for their environmental and food safety problems,there is a growing need for urgent exploration and identification of viable alternatives.Biogas slurry(BS)as the by-product of anaerobic digestion,possessing abundant macro-and micronutrients,is derived from a diverse range of raw materials,and large quantities of production,which can effectively suppress soil-borne diseases.However,the suppressive effect of BS on cucumber Fusarium wilt and its potential mechanism remains unclear.This study aimed to investigate the impact of various sources of biogas slurry,derived from pig manure,chicken manure,vinasse,and kitchen waste,on the incidence of cucumber Fusarium Wilt.Soil sterilization experiment,biogas slurry sterilization experiment and biofilm experiment,and rhizosphere colonization experiment were performed.Moreover,cucumber growth,the severity of cucumber Fusarium wilt,soil chemical properties,and microbia l community diversity and abundance of cucumber rhizosphere have been analyzed.The cucumber rhizosphere microbial community abundance and composition were analyzed by q PCR and Illumina Mi Seq sequencing,respectively.This study aimed to determine the optimal application rate(v/w)that yields the most effective suppressive on cucumber Fusarium wilt and reveal the effects of biotic and abiotic facto rs of BS on the disease suppression of BS.In addition,the potential mechanism of cucumber Fusarium wilt suppression by applying BS has also been revealed.Overall,this study could provide a theoretical basis for the application of BS fertilizer and the sustainable development of green agriculture.The results were shown below:(1)The optimal application rate of BS is 3%(v/w),which had the strongest suppression on the incidence and severity indexes of cucumber Fusarium wilt.Compared with no application of BS,the incidence and severity index of cucumber Fusarium wilt decreased by 47.41% to 55.00% and39.55% to 47.27%,respectively.The abundance of FOC in the cucumber rhizosphere decreased by61.10% to 75.35%.Meanwhile,cucumber plant dry weight was highest with an increase of 26.74%to 41.27% at this application rate.The effects of four biogas slurries with different application rates on soil chemical properties showed consistent trends.The different application rates of the four BSs significantly increased soil p H.The soil EC value,soil alkaline nitrogen,available potassium,and Olsen phosphorus(Olsen-P)contents also increased significantly with the increase of BS application rate.(2)The soil applied with BS was sterilized at different depths(50°C heat treatment,80°C heat treatment,and gamma-ray irradiation).The incidence of cucumber Fusarium wilt increased from41.44%-46.67% in the non-sterilized treatment to 70.34%-72.94% in the gamma-ray irradiation treatment,and the severity index of cucumber Fusarium wilt increased from 39.67-43.33 in the non-sterilized treatment to 64.00-68.01 in the gamma-ray irradiation sterilization treatment.(3)Soil applied with sterilized or non-sterilized BS can significantly alter the microbial community structure in cucumber rhizosphere,increasing the abundances of Bacillus and Pseudomonas spp.communities,and decreased the abundances of total fungi and FOC communities and the incidence and severity indexes of cucumber Fusarium wilt.However,the enhancement of Bacillus and Pseudomonas spp.community abundances,and the suppression of the rhizosphere FOC abundance and cucumber Fusarium wilt were significantly lower in BS sterilized with gamma-ray irradiation than those of the non-sterilized BS.(4)Pearson correlation analysis found that FOC abundance was significantly negatively correlated with the rhizosphere bacterial microbial community,abundances of total bacteria,Bacillus and Pseudomonas spp.and soil p H,but significantly positively correlated with the fungal community and total fungal abundance.Mantel test analysis revealed that disease incidence and severity indexes of cucumber Fusarium wilt were significantly correlated with the composition and abundances of total bacteria,total fungi,Bacillus spp.,Pseudomonas spp.,and FOC and soil p H.Based on these results,the soil p H,rhizosphere bacterial and fungal communities,FOC abundance,and incidence and severity indexes of cucumber Fusarium wilt were analyzed by Structural equation modeling(SEM)analysis.The SEM analysis revealed that soil p H did not directly suppress the occurrence of cucumber Fusarium wilt.However,it indirectly influenced disease suppression by regulating the composition of rhizosphere bacterial communities and reducing the abundance of Fusarium oxysporum f.sp.cucumerinum(FOC)in the rhizosphere.As the abundance of FOC in the rhizosphere plays a significant role in determining the severity of cucumber Fusarium wilt,the suppressive effect of the rhizosphere bacterial community indirectly impacted the disease’s progression.(5)Further analysis of the effect of different BSs application on the relevant taxa involved in Fusarium wilt suppression using rhizosphere bacterial community as a key factor for disease suppression.Different BSs affect the same disease suppression-related rhizosphere taxa,including OTU5540,OTU4049,and OTU4540,which were classified as Bacillus,and OTU5673 and OTU5630,which were classified as Pseudomonas.Random forest analysis showed that the soil p H,soil available nitrogen,Olsen-P and available potassium contents had a significant effect on these disease-suppression-related rhizosphere taxa.And the soil p H is the key environmental factor.(6)The same antagonistic strains were isolated from the four biogas slurries and four soils applied with different biogas slurry.Bacillus velezensis(B1)and Bacillus subtilis(B2)are isolated from the four biogas slurry samples.The common strains scre ened from the soil applied biogas slurry were Bacillus amyloliquefaciens(S1)and Bacillus subtilis(S2).These strains have the function of promoting cucumber growth and suppressing the cucumber Fusarium wilt.Biofilm and rhizosphere colonization experiment showed that the B1 and S2 strains co-culture could promote the formation of biofilm,improve their colonization in the cucumber rhizosphere,decrease rhizosphere FOC abundance and suppress cucumber Fusarium wilt.Sterilized BS pot experiment found that the change in soil chemical properties caused by BS application can enhance the ability of B1(Bacillus velezensis)+S2(Bacillus subtilis)to colonize cucumber rhizosphere and thus suppress the cucumber Fusarium wilt.In conclusion,the optimum application rate of different sources of BSs was 3%(v/w).The four BSs exhibited similar suppressive effect and mechanism at this application rate.Specifically,BS microbes can suppress the incidence of cucumber fusarium wilt by increasing the abundance of antagonistic bacteria in the rhizosphere colonization and reducing rhizosphere FOC abundance.Furthermore,the influence of BS microbes on rhizosp here microorganisms was strengthened by changing soil chemical properties,resulting in additional suppression of cucumber Fusarium wilt. |
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