| The plant parasitic nematode(PPN)is a plant disease that commonly infests the roots of plants and seriously affects the growth of plants.It is widespread in crops and caused global losses of about US$125 billion in 2012(Bissadou et al.,2012).Therefore,the prevention and treatment of root-knot nematodes cannot be delayed.The control methods of root-knot nematodes include physical control,chemical control,and biological control,among which the biological control has the advantages of safety,no pollution,and has wide application prospects.In this study,we isolated and screened strains with biocontrol effect against Meloidogyne incognita,studied its biocontrol effect and the pathway of biocontrol effect,and provided basis for the further development of a new plant parasitic nematode biocontrol agent.The main findings are as follows:(1)The acquisition of Meloidogyne incognita.From the roots of tomato infected with Meloidogyne incognita,7d of egg were picked to obtain a large number of second-instar larvae(J2)with strong activity.At the same time,the corresponding soil containing the Meloidogyne incognita was collected to provide materials for subsequent experiments.(2)Screening of nematicidal strains.By diluting the coating method,136 strains of bacteria,18 actinomycetes,and 8 strains of fungi were isolated from the collected samples.Through the contact test of the supernatant of the fermentation broth,11 strains of bacteria with good effects were screened out.After culturing in an LB liquid fermentation medium at37°C for 48 hours,the supernatant of the fermentation broth was corrected for death at the second instar larvae of Meloidogyne incognita at 12 h.The rate has reached more than 80%.(3)Biocontrol bacteria contact root-knot nematode pot experiment.Observing the control effect of biocontrol test bacteria on potted plants in contact with nematodes,F2 strain had the best control effect,and the number of single knots and heavy root knots was significantly lower than that of other treatment groups.The number of single knots was 51 and the number of heavy knots was 7.The inhibition rate of root knot was 83.33%.(4)Biocontrol bacteria induced plant system resistance pot test.The control effects of the20 d biocontrol bacteria F1,F2,F4,XN2#6,and P1#6 treatment groups were 72.73%,63.64%,72.73%,63.64%,and 63.64%,respectively.The control effects of the 30 d biocontrol bacteria F1,F2,F4,XN2 #6 and P1 #6 treatment groups were 61.54%,56.15%,53.85%,53.85% and61.54%,respectively.The biological control effect is basically stable.(5)Effects of Biocontrol Bacteria on the Growth of Tomato and Activity of Enzyme.The test-tolerant bacteria have different degrees of promoting effect on the growth of tomato.In particular,the F2 treated plants were significantly higher than the control group in terms of aboveground fresh weight,aboveground dry weight,underground fresh weight,underground dry weight,stem diameter and shoot height.It shows that the F2 strain can significantly promote plant growth.The five strains of bio-control bacteria have a certain increase effect on leaf enzyme activity,root enzyme activity,soil enzyme activity,and can increase plant resistance to pests and diseases.(6)Effect of Biocontrol F2 Strain on Expression of PI1 and PR1 Gene in Tomato Root.The biocontrol fungus F2 had no significant effect on the expression of the PI1 gene;there was a significant upregulation of the PR1 gene expression.It is speculated that the control of F2 strains on Meloidogyne incognita may be related to SA-mediated salicylic acid pathway.(7)Identification of biocontrol bacteria F2.According to the morphology,physiology,biochemistry and molecular biological identification,the biocontrol fungus F2 is Bacillus licheniformis.In summary,the biocontrol fungus F2 has a good control effect against the Meloidogyne incognita,which can significantly promote the growth of the plant and improve the plant's system resistance to pests and diseases.F2 can up-regulate the expression of PR1 gene,so its mechanism of controlling Meloidogyne incognita may be involved in salicylic acid(SA)pathway. |
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