| Tomato Fusarium wilt is a common and the most harmful soil-borne disease of tomato caused by the Fusarium oxysporum f.sp.lycopersici Snyder and Hansen.The occurrence and spread of tomato Fusarium wilt disease have been severely restricting the yield and sustainable development of tomato and caused huge economic losses during the widespread of facility agriculture,which has the characteristics of high intensiveness,single planting species,and high multiple cropping index.The key to control the soil-borne diseases is to reduce the number of pathogens in soil to the safe range for crops.Soil-borne pathogens live in the soil or a certain stage of their life in the soil.Their massive growth and reproduction are closely related to the degradation of soil properties,the enrichment of allelopathy,and the reduction of microbial community diversity.However,the existing control methods of tomato Fusarium wilt are mainly to protect plant and inactivate the pathogenic microbes.There are few researches from the following insights on the control mechanism of tomato Fusarium wilt,such as improving the soil ecological environment and constructing a healthy soil.In this study,tomato Fusarium wilt was used as the research object and the biochar was used as the soil amendment.Furthermore,we have explored the control effect tomato Fusarium wilt using biochar and the possible mechanism under biochar-mediated from the aspects of soil property,enzyme activity,and microbial community structure.The results are as follows:(1)Biochar had obvious inhibitory effect on Fusarium oxysporum in soil.In both of the biological treatment group(unsterilized soil,inoculated with Fusarium oxysporum)and the abiotic treatment group(sterilized soil,inoculated with Fusarium oxysporum),biochar and potassium humate could significantly reduce the number of Fusarium oxysporum in soil.The number of Fusarium oxysporum in soil first increased and then unchanged with the increasing of biochar contents.While with the increase of potassium humate contents,the number of Fusarium oxysporum in soil first decreased and then increased.The effect of biochar combined with potassium humate on the number of Fusarium oxysporum in soil was similar to that of potassium humate alone,which indicated that biochar had inhibitory effect on the growth of Fusarium oxysporum,while high amount of potassium humate(>1%)had a promoting effect on the growth of Fusarium oxysporum.In addition,correlation analysis showed that the number of Fusarium oxysporum in soil was closely related to physical and chemical properties of soil and its enzyme activities.Considering the above results,it was found that the effect of biochar on inhibiting Fusarium oxysporum and improving soil ecological environment was better than that of potassium humate.(2)Immobilization and deactivation of Fusarium oxysporum-produced cell wall degrading enzymes and toxic metabolites by biochar play an important role in the control of tomato Fusarium wilt.The adsorption experiment showed that the adsorption capacity of pectinase by biochar and activated carbon was greater than that of cellulase and the adsorption capacity of activated carbon was greater than that of biochar.The adsorbed enzymes were completely immobilized and observably deactivated.The activity of immobilized pectinase reduced to 43.01% under biochar treatment and 44.91% under activated carbon treatment,while the activity of the immobilized cellulase only retained1.88% under biochar treatment and 3.89% under activated carbon treatment.The tomato seedling bioassay analyses demonstrated that the adsorption of cell wall degrading enzymes and toxic metabolites contributed to reducing the disease severity and increasing the dry weight of tomato.(3)Biochar prepared at different pyrolysis temperatures and its properties(backbone and ash)had inhibitory effects on tomato Fusarium wilt.The pot experiment showed that the disease level of tomato Fusarium wilt significantly reduced with the application of biochar pyrolyzed at 300°C(B300)and 700°C(B700).Similarly,the treatment with backbone of the biochar pyrolyzed at different temperatures(named ex B300 and ex B700)reduced the incidence of tomato but the effect is weaker than that of the B300 and B700 treatments.Moreover,B300,B700,ex B300,and ex B700 showed a significant inhibitory ability on the number of Fusarium oxysporum in soil.The number of Fusarium oxysporum decreased by 33.87% for B300,38.17% for B700,27.85% for ex B300,and 50.77% for ex B700 treatments compared with the control.However,under the ash treatment of the biochar pyrolyzed at different temperatures(named Ash300 and Ash700),the incidence of tomato was similar to that of the control and the disease degree was not reduced.In addition,there was no significant difference in the number of Fusarium oxysporum in soil between the ash treatment and control.The analysis of soil microbial community diversity showed that biochar and its components had the potential to promote soil bacterial diversity but showed a tendency to inhibit fungal diversity.(4)Biochar mediated the assembly of root-associated microbiome of tomato root under the Fusarium oxysporum stress.The pot experiment showed that the Alpha diversity(Sobs index and PD index)of soil bacteria and fungi decreased gradually from the bulk soil,rhizosphere,and rhizoplane to the endosphere under all treatment.The biochar could obviously alleviate the changes in Alpha diversity caused by Fusarium oxysporum stress.According to the analysis of microbial community structure,results showed that the dominant bacterial included Proteobacteria,Actinobacteriota,Firmicutes,Chloroflexi,Gemmatimonadota,Bacteroidota,Myxococcota,Acidobacteriota,Nitrospirota,and Verrucomicrobiota.The dominant fungi included Ascomycota,Basidiomycota,Mortierellomycota,Chytridiomycota,and Glomeromycota.In addition,the results of the analysis of inter-group difference showed that there was a significant difference in the abundance of the dominant phyla of bacteria and fungi in each region of the root system.Fusarium oxysporum stress had different effects on microbes in different regions of the root system but the intervention of biochar could inhibit these effects to some extent.(5)Biochar could significantly inhibit tomato Fusarium wilt by inducing systemic resistance in tomato.Under the Fusarium oxysporum stress,the photosynthetic pigments and malondialdehyde content of tomato leaves increased significantly and the application of biochar significantly reduced the change in malondialdehyde content.The activity of peroxidase in tomato significantly reduced but the activity of "detoxification enzymes"(including catalase,superoxide dismutase,glutathione reductase and glutathione STransferase)significantly increased during the biochar treatment.The content of oxidized glutathione in tomato was significantly increased under Fusarium oxysporum stress.The application of biochar(3%)significantly reduced the content of oxidized glutathione but significantly increased the content of reduced glutathione,which indicated that the biochar can enhance the removal efficiency of active oxygen in tomato.In addition,application of biochar can enhance the priming effect and ability of tomato system against Fusarium oxysporum invasion,which is mainly dependent on the pathway mediated by jasmonic acid and ethylene.Specifically,with the treatment of biochar,the relative expression of salicylic acid-related genes(PR1a,MPK2,and NPR1)was down-regulated,while the relative expression of jasmonic acid-related genes(PDEF1,JAZ1,and JAZ3)and ethylene-related genes(ACO1 and ACS)was up-regulated.The above results indicated that the application of biochar could enhance the resistance ability of tomato system to defend against the Fusarium oxysporum stress.In summary,this study revealed that biochar inhibited the growth of Fusarium oxysporum by affecting soil physical and chemical properties,enzyme activities,root microbial community structure and other soil ecological environment,adsorbing cell wall degrading enzymes and toxic metabolites produced by Fusarium oxysporum to hinder its invasion to tomato roots,and finally inducing and improving tomato systemic resistance to stress caused by Fusarium oxysporum invasion.The results provide a new theoretical basis and technical support for the application of biochar in soil-borne disease control. |
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