| Cucumber Fusarium wilt and root knot nematode disease are devastating soil-borne fungus disease that limits the yield of cucumbers worldwide.At present,the application of biocontrol microorganisms for Fusarium wilt and root knot nematode has shown good control effects and has become the main direction of biological control in the future.Streptomyces albospinus CT205 is a biocontrol actinomycete that has been screened by the laboratory and has good antagonistic effects against a variety of pathogenic fungi.Its metabolically active substance is Cycloheximide.Studies have shown that it can inhibit the mycelial growth and spore germination of Fusarium oxysporum,and it also has good control effect on cucumber Fusarium wilt.This article firstly studied the effects of CT205 metabolically active substances on the enzyme production and toxin production of F.oxysporum.Secondly,the killing nematidal activity and inhibiting egg hatching ability of the active substances from CT205 were explored.The effect of CT205 solid preparation on cucumber root knot nematode disease was verified with pot experiment.Finally,CT205 biology agent was applied to soil culture and cucumber potted experiments.Based on the dynamic changes of CT205 and its active substances in the soil and the microbial diversity and community structure of cucumber rhizosphere soil,the mechanism of CT205 against cucumber soilborne wilt was further analyzed.The main findings are as follows:Through shaker culture experiments,it is found that CT205 metabolically active substances have effected on both the cell wall degrading enzymes and fusaric acid from F.oxysporum.After treatment with CT205 metabolically active substances and Cycloheximide standards,the abilities of F.oxysporum to produce cell wall degrading enzymes(pectinase enzyme,polygalacturonase enzyme,filter paper activity,endo-1,4-β-D-glucanohydrolase and exo-1,4-β-D-glucanohydrolase enzymes)were significantly reduced;Its ability to produce fusalic acid was also inhibited.The relative inhibition rate reached 14.09% with CT205 fermentation supernatant treatment.When the concentration of cycloheximide was40 μg/m L,the relative inhibition rate was 44.70%,and the concentration reached 100 μg/m L,the relative inhibition rate was 80.24%.The inhibitory effect of the crude toxins obtained by different treatments on the germination of cucumber seeds and the wilting effect on the seedlings were also weakened to varying degrees.It showed that CT205 metabolically active substances can reduce the ability of F.oxysporum to produce enzymes and toxins,and weakened the pathogenicity of F.oxysporum from the perspective of invasion,expansion and poisoning of host cells.The results of in vitro experiments showed that the fermentation supernatant of CT205 has strong nematicidal activity against root-knot nematode J2 s,with a corrected mortality rate of 91.21% at 24 h.It also has a strong anti-hatching effect on root-knot nematode eggs,and the relative inhibition rate can reach over 80% after 72 hours of treatment.The VOCs produced by CT205 can also significantly inhibit root-knot nematode J2 s.Pot experiments confirmed that CT205 microbial agent can effectively reduce the incidence of cucumber rootknot nematode disease while promoting the growth of cucumber plants,and has a good control effect on cucumber root-knot nematode disease,with a control effect of 45.80%.Preparation of CT205 biological agent for soil culture and pot experiment.The results of soil culture experiments showed that CT205 biological agent can maintain a relatively stable level of cells in a certain period of time.The Cycloheximide produced by CT205 and its standard showed a downward trend in the soil environment,after 28 days,it still had an inhibitory effect on F.oxysporum.It indicated that CT205 can directly antagonize F.oxysporum by producing active substances in the soil environment.and the Cycloheximide and standard products produced by its metabolism show a downward trend in the soil environment,but it can still align the tip after 28 days.The inhibitory effect of Fusarium spores shows that CT205 can directly antagonize F.oxysporum by producing active substances in the soil environment.The pot experiment confirmed that the treatment of CT205 and Cycloheximide can significantly reduce the number of F.oxysporum in the soil and reduce the incidence of cucumber wilt.After sequencing by Illumina PE250,it was found that CT205 and Cycloheximide treatment had higher bacterial species richness and species diversity,CPCo A analysis also showed that the similarity of soil bacterial and fungal community structure under different treatments was low.At the level of phylum classification,the relative abundance of Proteobacteria and Actinomycota was higher in CT205 treatment;the relative abundance of Ascomycota was highest in Cycloheximide treatment.At the level of genus classification,the relative abundance of pathogenic microbes such as Fusarium,Ralstonia,Cladosporium,Chaetomium,Curvularia in CK treatment was significantly higher than those in other treatments,and these pathogenic microbes were positively correlated with Fusarium.The abundance of beneficial bacteria such as Sphingomonas,Lysobacter,Pseudomonas,Bacillus,Flavobacterium,and Haliangium and beneficial fungi such as Arthrosporum,Aspergillus and Trichoderma in CT205 and Cycloheximide treatments was higher than those in CK treatment.In addition,beneficial bacteria such as Thermomonas,Mortierella,Conchotomy,Achromobacter,Stenotrophomonas and other beneficial bacteria also had higher levels in CT205 treatment.Spearman rank correlation analysis showed that most of the beneficial bacteria genera are negatively correlated with Fusarium,the increase of these beneficial bacteria genera has a certain restrictive effect on Fusarium.The above results showed that the application of CT205 biological agent can stimulate the increase of beneficial functional bacteria in the soil,while reducing the abundance of pathogenic bacteria.It showed that CT205 can not only produce active substances to inhibit pathogenic microbes,but also improve the rhizosphere microbial community structure,so as to achieve the purpose of inhibiting soil-borne Fusarium wilt. |
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