Study On The Control Of Aspergillus Niger Against Root-knot Nematode

Root-knot nematodes are a serious economic hazard to crops.Control of root-knot nematodes by biological agents not only can effectively control the occurrence of nematode diseases,but also can reduce the impact on the environment.It is an ideal method for nematode control.Among the many biological control fungicides,Aspergillus niger can survive in many natural conditions and has widely adaptability.It has great potential application in the biological control field of root-knot nematode.Aspergillus niger H1-1 strain is obtained early that has a strong effect on nematodes.We can use it to understand the mechanism of this strain on root-knot nematodes,optimize the acquisition conditions and preparation methods of effective action factors on nematodes,and evaluate the strains against soil conditions.For the control effect of root-knot nematodes and the impact on soil microbial diversity,microcapsule technology was used to improve the bacterial agent dosage form of H1-1strain,thereby enhancing the control effect of the bacterial agent on root-knot nematodes in soil.1.Through the observation of colony morphology,microstructure and physiological characteristics,the best growth temperature of strain H1-1 is 26?,and the best pH is 4⁵.After ITS comparison and phylogenetic analysis,the target strain is Aspergillus niger.2.It was found that the active substance of Aspergillus niger strain H1-1 against root-knot nematode has the following characteristics:not protein,non-volatile,easily soluble in organic solvents,and petroleum ether and acetone in organic solvents 10:1and 2:1 elution at a certain ratio.3.Optimizing the fermentation conditions.After adding sucrose,soybean meal and magnesium sulfate to the medium,it is verified by fermentation in 20-liter and50-liter fermentors.Compared with the shake flask,the time of the fermentation of the lethal active ingredient to root-knot nematodes is advanced.The lethality of the fermentation broth to nematodes is stable at 99%,and it has the technological basis for further scale-up fermentation.The optimal medium for the strain to produce nematicidal active metabolites:PDA medium(sucrose instead of glucose in the medium),supplemented with 3%soybean meal and 0.5%magnesium sulfate.4.The effect of fermentation broth of H1-1 strain on root-knot nematodes:the lethal rate at 2 h is 94%,and the hatching inhibition rate of nematode eggs is 86%.Fermentation filtrate extracts and spore suspensions of different concentrations of Aspergillus niger H1-1 were applied to potted soil infested with second-instar root knot nematode(J2s).Compared with the untreated control group,fermentation broth and spore suspensions were applied.The prevention effect after liquid reached 89.17%and94.16%respectively.5.Using sodium alginate as a carrier,prepare microcapsules of H1-1 strain by embedding method.It is ideal to select 1.0%CaCl₂ and 1.0%sodium alginate.After 30days of application of the microcapsule formulation in the soil,the application rate was22.5 kg/hm² and 30 kg/hm²,and the control effect reached 91.77%and 93.47%,respectively.The results indicate that the preparation of microbial agents by microcapsules can improve the survival rate and prevention effects of the microbial agent in the soil.6.After applying the fermentation broth of H1-1 strain,the microbial diversity of tomato root soil is affected by different degrees.After the fermentation broth affects tomatoes,it had little effect on the diversity of bacterial communities and a great influence on the diversity of fungal communities.