| Under stress,root exudates of plant can be changed and further lead to the change of rhizosphere bacterial community.This study focused on the changes of tomato root exudates after root-knot nematodes（RKNs）infection and response of proteus vulgsris BX,which had both nematidical activity and chemotactic activity towards tomato root exudates.The interaction between root exudates and rhizosphere bacteria under nematodes stress was investigated.Three strains of Proteus vulgaris BX,Bacillus pumilus J-1 and Enterobacter asburiae B13 with strong activities were evaluated.The nematidical activity of the fermentation broth at 24 h were 89.91%,92.92%and 92.73%,respectively.Compared with healthy plants,the chemotactic index of strains to tomato root exudates infected by Meloidogyne incognita were 2.09,2.44 and 1.82,respectively.In pot experiment,strain BX significantly inhibit the infestation of tomato by M.incognita.The number of nematodes in the root decreased 77.04%,and the galls of tomato root reduced 76.76%after added fermentation broth.The number of nematodes in the root decreased 81.18%and the galls of tomato root reduced 83.05%after supplemented fermentation broth again at day 17.In the early 10 days,no galls were found in tomato root,and there was no significant difference in the colonization of BX in tomato root and rhizosphere soil compared with healthy plant.However,the amount of BX colonization in tomato root and rhizosphere soil were significantly higher than healthy plant at the 20-30 days.The changes of infected tomato root exudates were compared with metabolomics.Among the 354 differential metabolites obtained from the metabolome,17 compounds were screened the chemotactic activity to the three strains.Among them,caffeic acid,coumarin,salicylic acid,sebacic acid,and syringic acid have strong attraction to strain BX,and the maximum chemotactic values are 1.71,1.85,1.88,1.82,1.59 at concentrations 10-6 mg/mL,10-2 mg/mL,10-3 mg/mL、10-4 mg/mL and 10-4mg/mL,respectively.Homovanillic acid,2-（4-hydroxyphen）ethanol,and myristic acid have strong repellent activity,and the maximum chemotactic values are 0.34、0.46、0.15 at concentrations 1 mg/mL、10-2 mg/mL、1 mg/mL respectively.Compounds 2-（4-hydroxyphen）ethanol and myrcene have strong attraction to strain J-1,and the maximum chemotactic values are 2.74、2.78 at concentrations 10-5 mg/mL、10-3 mg/mL,respectively.Compounds（-）-naringenin、myristic acid have strong repellent activity,and the maximum chemotactic values are 0.44、0.40 at concentrations 10-6 mg/mL、10-1 mg/mL,respectively.Compounds 2-（4-hydroxyphen）ethanol、myrcene and menthone have strong attraction to strain B13,and the maximum chemotactic values are 2.84、2.24、2.46 at concentrations 10-6 mg/mL、1 mg/mL、10-1 mg/mL,respectively.Compound（-）-naringenin has strong repellent activity to B13 at the concentration of 1mg/mL.The main KEGG pathway of these metabolites were phenylpropanoid biosynthesis、tyrosine metabolism、monoterpenoid biosynthesis、isoflavonoid biosynthesis and plant hormone signal transduction.At the same time,the nematicidal crude extract of ethyl acetate phase of fermentation broth of strain BX was isolated by activity tracing.It was found that indole was one of its active components.The nematidical activity of indole reached 93.42%at 24 h at concentration 1 mg/mL.In this study,it was found that the root exudates of tomato were significantly changed after the infection of RKNs,and the nematidical strain BX could significantly attracted by the tomato root after the formation of galls.Compounds that caused the chemotaxis were determined by comparing metabolomics.These compounds promoted the chemotaxis and colonization of strain BX,then improved the nematicidal efficiency.These results provide a new clue for the development of effective nematode control agent. |
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