Screening Of Four Plant Nematodes Biocontrol Fungi And Basic Research On The Application

Plant nematodes are one of the main pathogens that cause plant diseases.They occur globally,and their host range is extremely wide,causing serious damage.The annual economic loss to the world is as high as US$125 billion.In this study,Globodera rostochiensis was used as the material to isolate and purify the parasitic fungi from the cysts,which were preliminarily identified by combining morphological and molecular biological methods,and the isolation frequency of fungi of each genus was counted.According to the morphological and ITS comparison results,40 representative fungi were selected as the test strains,and their biocontrol potential to G.rostochiensis,rice stem tip nematode(Aphelenchoides besseyi),pine wood nematode(Bursaphelenchus xylophilus),and Ditylenchus destructor four kinds of plant nematodes,screened out the biocontrol fungi with the strongest nematicidal activity under each nematicidal method.By combining morphology and molecular biology,the classification status of biocontrol fungi was clarified,the biological characteristics of some strains were explored,and secondary metabolites of biocontrol fungi were further extracted for preliminary nematicidal activity determination.The conclusions are as follows:1.Through the isolation and purification of parasitic fungi from the potato golden nematodes collected from different locations in Guizhou Province,a total of135 fungi were obtained,belonging to 23 genera,of which Fusarium was the most frequently isolated fungus.79 strains,with an isolation rate of 58.52%;followed by15 strains of Penicillium,with an isolation frequency of 11.11%;5 strains of Edenia and Paraphaeosphaeria,with an isolation frequency of 3.7%;a total of 4Gongronella strains,with an isolation frequency of 2.96%,There were 3 strains of Chaetomium and Trichoderma,and the isolation frequency was 2.22%;Arxotrichum,Didymella,Neocosmospora,Phanerochaete,Mortierella with 2 isolates each with a segregation frequency of 1.48%,and 1 isolate from each of the remaining 11 genera,with the lowest segregation frequency of 0.74%.2.The parasitization test of the tested strains on the cysts and eggs of G.rostochiensis,found that all the tested fungi had parasitic phenomena on the cysts,and there were 25 fungi with a relative parasitic rate of 100% to the cysts;17spore-forming fungi had spore suspensions.After 9 days of solution treatment of the eggs,only the strain GUCC2236 did not appear parasitic,and all the other strains could parasitize the eggs,and the relative parasitic rate was as high as 71.66%(GUCC2219);Secondly,the relative parasitic rate of strain GUCC2200 to cyst nematode eggs was 35.56%;the relative parasitism rates of other strains to the eggs were not high.3.Through the determination of the nematicidal activity of the tested fungal fermentation broth against three plant nematodes,A.besseyi,B.xylophilus,D.destructor,it was found that the corrected mortality rate of the tested fungal fermentation broth for the three plant nematodes was greater than 80%.The strains were 14,12,and 21,respectively.A total of 7 strains of fungal fermentation broth had corrected mortality rates of more than 80% for the three plant nematodes.The 7strains were numbered GUCC2204,GUCC2212,GUCC2216,GUCC2224,and GUCC2229,GUCC2232,GUCC2238.In addition,the fermentation broth of strain GUCC2204 could kill more than 80% of the nematodes within 12 hours.4.Using water agar plates to test the predation of the tested fungi to three kinds of plant nematodes,A.besseyi,B.xylophilus,D.destructor,it was found that there were 3 test strains that had predation on the three kinds of plant nematodes,namely GUCC2217,GUCC2219 and GUCC2239.Among them,GUCC2219 has the highest predation rate to two of the three plant nematodes at 72 h,and its predation rate to the three plant nematodes reaches 54.43%,25.25%,and 46.56%,respectively.5.The biocontrol fungi were identified by the combination of morphological and molecular biological characteristics.Finally,8 strains of fungi with the best biocontrol effect,GUCC2204,GUCC2212,GUCC2216,GUCC2219,GUCC2224,GUCC2229,GUCC2232 and GUCC2238,were identified as: unknow species of Nigrospora(Nigrospora sp),known species of Neocosmospora(Neo.stercicola),known species of Arxotrichum(A.wyomingense),known species of Volutella(V.citrinella),known species of Gongronella(G.butleri),known species of Trichoderma(T.gamsii),known species of Penicillium(P.cremeogriseum)respectively.6.By exploring the biological characteristics of strains GUCC2204 and GUCC2219,as well as the extraction of secondary metabolites of strain GUCC2204 and the determination of nematicide activity of crude extracts,it was found that strain GUCC2204 grew well under natural culture conditions,and strain GUCC2219 had no effect on culture conditions.The requirements are harsher,and it is more suitable for the growth of the fungus under alkaline conditions;the crude extract of the secondary metabolite of strain GUCC2204 has nematicidal activity against three plant nematodes,and the 20-fold dilution has the highest activity against the three plant nematodes,and the active The order was D.destructor = B.xylophilus > A.besseyi;50-fold dilution took the second place,and the order of activity was D.destructor > B.xylophilus > A.besseyi;1 000-fold dilution still had low nematicidal activity against the three plant nematodes.