Investigation On Root-knot Nematodes Of Vegetable Facilities In Shandong, Biocontrol Experiment Of Strain AMCC1001028 And Its Fermentation Optimization

Root knot nematode is a plant-parasitic nematode which commonly found in vegetable greenhouses in Shandong province.It causes much economic losses every year,which has became an important factor restricting the development of vegetable greenhouses.Chemical pesticides cause environmental pollutions and damage the ecological system meanwhile,the quality of vegetable crops will also be influenced.Biological control has attracted more and more attention.In this study,several vegetable greenhouse bases in Shandong province were sampled to determine the type of root-knot nematode,and based on this,to explore the biocontrol experiments which strain AMCC1001028 worked on Meloidogyne incognita and its initial optimization of fermentation processing based on this.Here are the mainly resul:?1?Seven sites in four regions of Shandong?including Jinan,Weifang and Linyi?were sampled to determine the population density and the species of nematodes.The results showed that the highest density of root knot nematode population in the samples was 96.2ind·g^-1soil.Three common root-knot nematodes were detected by SCAR-PCR,including southern root-knot nematode,peanut root-knot nematode,and northern root-knot nematode.There were 6 infested samples and 1 compound infested sample.The southern root-knot nematode was the dominant species.?2?The effect of the fermentation supernatant from the biocontrol strain on the second-instar larvae of the southern root-knot nematode showed that the lethality rates of the second-instar larvae with 48h fermentation supernatants treatment for 12h and 24h,were87.22%and 100%,respectively.The active compound remained high nematicidal activity after acid and alkali treatments as well as cold/heat treatment.The pot experiment of the biocontrol bacteria showed that the number of the larvae and the oocysts in the biocontrol bacteria treatment decreased by 28.81%and 50.85%respectively.It showed that the biocontrol bacteria owned biocontrol potential against root knot nematodes and had a good development prospect.?3?Optimization of the fermentation conditions for biocontrol bacteria.One basic medium was selected by the higest cell count and spore count from ten existing basal cultures.Single factor test was conducted on shake flask culture conditions.As the result,the optimum temperature was 37°C,the optimal liquid loading was 10%,the optimal inoculum was 4%,and the optimal initial pH was 7.0.Corn meal was verified as the best carbon source in the fermentation basal medium,and bean cake powder in the fermentation basal medium was the best nitrogen source.The Plackett-Burman test was adopted and corn meal,bean meal and calcium carbonate were verified to be significant for the amount of bacterial cells.Response surface optimization can optimize three significant factors to determine as X₁=2.94,X₂=2.46,X₃=0.18.The optimized fermentation medium was corn meal 29.4 g/L,bean cake powder24.6 g/L,calcium carbonate 1.82 g/L,ammo nium sulfate 1.0 g/L,magnesium sulfate 0.1 g/L,and potassium dihydrogen phosphate 2.1 g/L,manganese sulfate 0.5g/L.By using the optimized culture medium,the bacteria number in the fermentation broth reached 1.50×10¹⁰CFU/mL,which was 30.43%higher than the basis culture medium.