Studies On The Pathogenicity Of Duddingtonia Flagrans To Meloidogyne Incognita

Plant-parasitic nematodes cause huge economic losses to agriculture every year,and face great challenges in controlling them.Duddingtonia flagrans is a nematode-trapping fungus.It can generate adhesive three-dimensional net-type traps that capture and kill nematodes,so it has certain potential in controlling parasitic nematodes.It produces chlamydospores which can resist various harsh environments and are excreted with animal feces through the gastrointestinal tract,so it is currently mainly used to control animal parasitic nematodes.In this paper,the nematode-trapping fungus D.flagrans was taken as the research object,and taking Meloidogyne incognita as the target,the pathogenic process of M.incognita was observed by light microscope and scanning electron microscope;the secondary metabolites including volatile and non-volatile components were studied and the activity was determined;the transcriptome of nematode predation process by fungus was analyzed.The pathogenicity study of D.flagrans to plant root-knot nematodes,will provide theoretical basis for its use in the control of plant root-knot nematodes.1.Morphology and pathogenicity of D.flagransThe morphological structures of the hyphae,conidia and chlamydospores of D.flagrans were observed and described.The pathogenicity process of D.flagrans against C.elegans,P.redivivus and M.incognita was observed by optical microscope;and the effect on egg hatching of M.incognita was assayed.Scanning electron microscope observation was carried out and described on the interaction process between D.flagrans and M.incognita.2.The volatile components of D.flagransThe YPD liquid medium was used for culturing D.flagrans,and the activity assay showed that the volatile components produced by the fungus had nematicidal activity.Using gas chromatography-mass spectrometry to analyze the volatile components in the fermentation broth of D.flagrans,52 metabolites were identified,and 11 major compounds were tested for their nematicidal activity.The results showed that cyclohexanamine,cyclohexanone,and cyclohexanol have obvious nematicidal activity against M.incognita.Further experiments proved that these three metabolites can also inhibit the egg hatching of M.incognita.Among them,cyclohexanamine has the strongest activity.When the concentration of cyclohexanamine is 8.71 μM,the nematicidal activity against M.incognita reaches 97.93% at 12 h;and at the concentration of 26.14 μM,it shows obvious inhibitory effect on egg hatching of M.incognita.3.Studies on the secondary metabolites of D.flagransThe YPD liquid medium was used to ferment D.flagrans,and 8 compounds were isolated and identified from the ethyl acetate extracts of the fermentation products.They are 3,4-furandiol(WAF-1),(3β,5α,6β,22E)-3,5,6-triol-7,22-diene-ergosta(WAF-3),N-acetyltyramine(WAF-4),cyclo(Trp-Gly)(WAF-9),indolecarboxylic acid(WAF-14),N-(2-phenylethyl)acetamide(WAF-15),N-(2-hydroxyphenethyl)acetamide(WAF-17),4-hydroxy-benzene acetic acid(WAF-18).4.Transcriptome analysis of the nematode predation process by D.flagransUsing the whole genome of D.flagrans as a reference,transcriptome sequencing was performed on samples of D.flagrans interacting with nematodes at 0 h,3 h,7 h,12 h,and 24 h.The results showed that a total of 6293 genes were differentially expressed in the process of predation of nematodes by D.flagrans,of which 2012 and2834 genes were up-regulated and down-regulated,respectively.The GO function analysis of the differentially expressed genes showed that genes related to metabolic process,catalytic activity and cell membrane changed significantly.KEGG enrichment analysis showed that among the up-regulated genes,the number of genes enriched in autophagy,proteasome and propionate metabolism was high,indicating that requires a large amount of proteolytic enzymes in the process of preying nematodes.Among the down-regulated genes,more genes were enriched in amino acid biosynthesis,selenium compound metabolism,arginine biosynthesis,and nitrogen metabolism,indicating that the synthesis related to fungal saprophytic effect was weakened.The innovation of this paper:1.The volatile metabolites cyclohexanamine,cyclohexanone and cyclohexanol produced by D.flagrans with nematicidal activity against M.incognita and inhibiting the hatching of M.incognita eggs were found for the first time.2.Using electron microscope to observe the interaction process between D.flagrans and M.incognita,it was found that D.flagrans could form a trap to capture M.incognita,and the sticky substance on the trap could stick to the southern root knot nematode.