| Fusarium wilt diseases,caused by formae speciales of the fungus Fusarium oxysporum are a serious problem for the production of cucumber,watermelon and other plants around the world.Soil pretreatment,such as soil fumigation,has been widely used to control weeds,plant parasitic nematodes,soil-borne fungi,insects,and other disease organisms in high-value agricultural production systems.Moreover,many studies have demonstrated that biocontrol is an effective strategy for controlling soil-borne diseases.In this study,effects of combined utilization of soil fumigation and bio-organic fertilizer on Fusarium wilt disease of cucumber and watermelon were investigated.The fumigation agent ammonium bicarbonate,which releases ammonia and showed an inhibitory effect on growth of Fusarium oxysporum in the cultural condition,was investigated when applied alone and with lime as a direct soil amendment under sealed conditions.For the Fusarium oxysporum f.sp.cucumerinum(FOC),and Fusarium oxysporum f.sp.niveum(FON),the suitable additive concentrations of ammonium bicarbonate was 2 g·kg-1 soil dry weight(DW),when applied alone.Ammonium bicarbonate had a stronger antifungal effect when mixed with lime(2 g·kg-1 for FOC;4 g·kg-1 for FON)than when applied alone in the pot experiments.In the field experiment,stronger antifungal effects were observed when the pH value of the soil was less than 7,and no significant difference between the two treatments was observed in alkaline soil.Moreover,these concentrations produced the best effects when short processing times,broad temperature ranges and wide soil moisture contents were used.Effects of combined utilization of the novel soil fumigation strategy and application of bio-organic fertilizer produced by Bacillus amyloliquefaciens SQR-9 on Fusarium wilt disease of cucumber and watermelon were investigated in the greenhouse and field experiments.Pot and field experiments were set up six treatments as following:1)LAB-BOF:the soil was treated with ammonium bicarbonate and lime before the application of the bio-organic fertilizer(BOF);2)LAB-OF:the soil was treated with ammonium bicarbonate and lime before the application of the common organic fertilizer(OF);3)AB-BOF:the soil was treated with ammonium bicarbonate before the application of the bio-organic fertilizer(BOF);4)AB-OF:the soil was treated with ammonium bicarbonate before the application of the common organic fertilizer(OF);5)CK-BOF:the soil was applied with bio-organic fertilizer(BOF);6)CK-OF:the soil was applied with common organic fertilizer(OF).Results from the pot experiment showed that compared to the control,disease control efficiency on watermelon and cucumber after application of bio-organic fertilizer was 22.22%and 14.29%,respectively,while combined application of bio-organic fertilizer and soil fumigation significantly improved the control efficiency,among which LAB-BOF treatments showed highest control efficiency of 88.88%for watermelon and 85.72%for cucumber,respectively.Based on cultural-dependent method,the number of FOC and FON were reduced by 71.38%and 95.50%after soil fumigation with ammonium bicarbonate and lime mixture which also showed the lowest number of culturable fungi,bacteria and actinomycetes and decreased by 64.3%and 87.31%after soil fumigation with ammonium bicarbonate.Results from physical and chemical properties showed that soil pH,total nitrogen,ammonium nitrogen and nitrate nitrogen contents were improved after fumigation while the content of total organic carbon reduced.In addition,no significant effects on the watermelon and cucumber plants growth were observed after soil fumigation and the bio-organic fertilizer can promote the growth of plants.Field experiment results showed that compared to the control,disease control efficiency on watermelon and cucumber after application of bio-organic fertilizer was were 20%and 19.62%respectively.Combined application of bio-organic fertilizer and soil fumigation with a mixture of ammonium bicarbonate and lime showed efficient control efficiency of 96%or watermelon and 58.83%for cucumber,respectively.The numbers of FON were reduced by 80.47%and 63.42%after soil fumigation with ammonium bicarbonate alone and mixed with lime,respectively.While the number of FOC decreased by 73.13%after fumigation with the mixture.In order to further study the relationship between soil microflora and Fusarium wilt disease,soil microflora in samples collected from the watermelon and cucumber fields were investigated by MiSeq high-throughput sequencing technology.Results showed that,in cucumber field,compared to the control,the relative abundances of Proteobacteria,Gemmatimonadetes,Verrucomicrobia,Acidobacteria,Firmicutes,Basidiomycota and Zygomycota were improved,while the value for Bacteroidetes,Actinobacteria,Ascomycota and Chytridiomycota were decreased after soil fumigation.In watermelon field,compared to the control,the relative abundances of Bacteroidetes,Gemmatimonadetes,Deinococcus-Thermus,Parcubacteria,Zygomycota and Basidiomycota were improved,while the value for Proteobacteria,Acidobacteria,Actinobacteria,Ascomycota and Chytridiomycota were decreased after soil fumigation.Among these phyla,a strong negative correlation between Gemmatimonadetes,Verrucomicrobia and Zygomycota and the disease incidence of cucumber and a clear positive correlation between Proteobacteria,Chlamydiae,Ascomycota and Basidiomycota and the disease incidence of cucumber were observed.Among these genus,a strong negative correlation between Gemmatimonas and Mortierella and the disease incidence of cucumber and a clear positive correlation between Simkania,Ktedonobacter,Geomyces,Cladosporium,Fusarium,Thielavia,Sarocladium,Botryotinia,Scedosporium,Micromonosporineae,Phycisphaera and Wallemia and the disease incidence of cucumber were observed.Among these phyla,a strong negative correlation between Chloroflexi,Gemmatimonadetes,Parcubacteria,Deinococcus-Thermus and Firmicutes and the disease incidence of watermelon and a clear positive correlation between Acidobacteria,Actinobacteria,Verrucomicrobia,Planctomycetes and Ascomycota and the disease incidence of watermelon were observed.Among these genus,a strong negative correlation between Gemmatimonas,Bellilinea,Kriegella,Blastopirellula and Conexibacteraceae and the disease incidence of watermelon and a clear positive correlation between Polyangiaceae,Propionibacterineae,Skermanella,Emericellopsis,Fusarium,Gibberella,Sarocladium,Humicola,Gibellulopsis,Aspergillus,Diaporthe and Guehomyces and the disease incidence of watermelon were observed.In summary,soil fumigation effectively suppressed the occurrence of Fusarium wilt disease for watermelon and cucumber and altered the soil microbial community structure and soil properties. |
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