Analysis Of The Biocontrol Efficacy Of Bacillus Velezensis Strain Bv-25 Against Meloidogyne Incognita

Root-knot nematode is an obligate parasitic nematode with a wide variety of hosts,which causes huge economic losses every year.Currently,there is no low-cost,safe and effective prevention and control method.Therefore,it is urgent to find new ways of biological control.There are a large number of beneficial microorganisms in the rhizosphere of plants,and there are many biocontrol resources,which have a broad application prospect.In this study,Bacillus velezensis strain Bv-25 was obtained from cucumber rhizosphere soil,and the biocontrol activity of Bacillus velezensis strain Bv-25 against root-knot nematode nematode was identified and the expression of resistance genes induced by Bacillus velezensis strain Bv-25was analyzed.The main results were as follows:1.The strain Bv-25 had strong nematocidal activity,and the fatality rate of its fermentation broth against the second instar larvae(J2s)was 100%within 12 hours.The strain had a strong inhibitory activity against the hatching of Rhizoctonia nucifera eggs,and the hatching rate of Rhizoctonia nucifera eggs treated with the fermentation broth was only 1.8%.The bacteria could colonize cucumber roots,and the number of bacteria attached to cucumber roots was 1.69×10~6CFU/g within 3h,and the infection rate of root knot nematode was effectively reduced by 98.6%.The strain upregulated the expression of defense response genes PR1.PR3.LOX1 and CTR1 in cucumber,inducing cucumber resistance to root-knot nematode.Potted and field experiments showed that the fermentation broth of the strain could reduce cucumber root knot by 73.8%and 67.1%,respectively.2.The volatile organic compounds of strain Bv-25 also showed biocontrol activity against root-knot nematode.The avoidance rate of volatile organic compounds was 85.2%,and the volatile organic compounds could inhibit the expression of MAPK.FLP and MI-ORD genes.The volatile organic compounds could inhibit the expression of MAPK.FLP and MI-ORD.The expression levels of Re-MAPK-1,Re-FLP-18 and Mi-ORD-1 were decreased by 98.5%,96.8%and 99.2%,respectively,after 48h fumigation with volatile organic compounds.Cucumber root knots were reduced by 34.1%after treatment with volatile organic compounds.Thirty-nine volatile organic compounds were identified by solid phase microextraction and gas chromatography-mass spectrometry.Among them,2-heptanone,3-methyl thiobutyrate S-methyl ester,dimethyl disulfide,trichloromethane and 2,6-dimethylpyrazine had inhibitory effects on root-knot nematodes.In general,Bacillus velezensis strain Bv-25and volatile organic matter have a good control effect against root-knot nematode nematode,and have the potential to develop new biocontrol agents.