| Meloidogyne incognita is one of the most important pathogenic nematodes in the worldwide.Endophytic bacteria,as a reliable biological control resource,is currently considered as a safe and effective resource for controlling root-knot nematodes.The endophytic Bacillus cereus BCM2 strain showed remarkable control effects on M.incognita.This study was designed to explore the mechanism of the endophytic bacteria BCM2 on tomato root exudates and M.incognita infection,so as to provide the theoretical basis for the control of root-knot nematodes by endophytic bacteria.In this study,we collected the root exudates of tomato plants colonized by BCM2,and found its repellent effect on M.incognita J2 through water agar plate assay and the linked twin-pot assay.The effect of BCM2 colonization on root exudates was analyzed by gas chromatography-mass spectrometry(GC-MS),and the main differentially active substances of tomato root exudates from tomato plants inoculated with BCM2 and those from plants treated with sterile water only were found.The effects of these differentially active substances on the hatching of M.incognita eggs,M.incognita J2 survival,movement of M.incognita J2 and the control effects were further analyzed.The effects of these different active substances on the seed germination rate and seedling growth and development of tomato plants were determined.1.The endophytic Bacillus cereus BCM2 colonized tomato roots could change the tomato root exudates,leading to an increase in the content of some substances,and then repelled the M.incognita J2.It was confirmed that the substances that have a repellent effect on nematodes were 3,3-dimethyloctane,n-tridecane and 2,4-di-tert-butylphenol.They were found to have a concentration gradient effect on the hatching inhibition rate,lethality and repellency of M.incognita,with increasing concentration,the higher the hatching inhibition rate,the higher the lethality and the stronger the repellency.In the pot experiment,the control effect on M.incognita also showed the concentration gradient effect.All three substances could reduce the infection of M.incognita to a certain extent.3,3-dimethyloctane,n-tridecane and 2,4-di-tert-butylphenol at 80 mmol/L,100 mmol/L and 6 mmol/L showed remarkable control effects with no significant difference from chemical insecticide fosthiazate,reaching 81.03%,71.40% and 71.91%,respectively.2.In the concentration range of 10~100 mmol/L,3,3-dimethyloctane and n-tridecane were found to have an inhibitory effect on tomato seed germination,and the inhibitory effect increased with increasing concentration.2,4-di-tert-butylphenol on the germination of tomato seeds was “low promotion and high inhibition”,at a concentration of 3 mmol/L,the highest was reached.At a certain concentration,the three substances had no effect on the growth parameters(plant height,aboveground fresh weight,aboveground dry weight,chlorophyll content)of tomato seedlings.3,3-dimethyloctane and n-tridecane inhibited the root activity of tomato seedlings at a concentration of 20 mmol/L,and the inhibitory effect increased with increasing concentration.2,4-di-tert-butylphenol inhibited the root activity of tomato seedlings at a concentration of 4 mmol/L,and the inhibitory effect increased with increasing concentration.3.2,4-di-tert-butylphenol showed remarkable control effects on M.incognita in the field.There was no significant difference between the chemical insecticide fosthiazate and 2,4-di-tert-butylphenol at 6 mmol/L and 8 mmol/L,which reduced the tomato root-knot index by 50.57% and 51.45%,and the number of rhizosphere soil nematodes decreased by 32.41% and 49.36%,respectively.At the same time,the tomato yield increased by 35.75% and 83.74%,promoted the growth of tomato significantly. |
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