Effects Of Four Important Nematode Pathogenic Fungi On Plants And Study On The Functions Of Two P450 Genes In Arthrobotrys Oligospora

Plant parasitic nematodes are a globally difficult-to-control,soil-borne disease that causes direct economic losses that increase year by year.The biological control of plant parasitic nematodes has been paid more and more attention due to the increasingly obvious environmental hazards.Nematode egg parasitic fungus Pochonia chlamydosporia YMF 1.00613,(PC),nematode-trapping fungus Arthrobotrys oligospora YMF 1.3170(AO)and its three mutants AOL_s00215g281,AOL_s00215g282,AOL_s00215g283(AO281,AO282 and AO283),insect pathogenic fungus Penicillium YMF 1.00864(PE)and thermophilic fungus Thermomyces dupontii YM 3-4(TD)are four important nematode pathogenic fungi.The field control effect of a single biocontrol strain is susceptible to environmental factors(temperature,soil pH,nutrients,etc.),resulting in reduced control effectiveness.In this paper,pot experiments were carried out to study the root knot nematode control efficacy by using TD in combination with P.chlamydosporia(PC),A.oligospora(AO)and three mutant strains(AO281,AO282 and AO283)and Penicillium.(PE)respectively,the results are as follows:Since the optimum growth temperature for the thermophilic Dubang fungus(TD)is 45 ?C,the TD is first composted.The results showed that TD could significantly inhibit the infection of root-knot nematodes against host plants,and the inhibition rate was 24.32%.Effects of nematode-trapping fungus AO and its three mutants,nematode egg parasitic fungus PC and insect pathogenic fungus PE on plants were further evaluated in the compost soil treated with thermophilic fungus TD.The results showed that fungi PC,PE,AO,AO281,AO282 and AO283 promoted the growth of plant roots and reduced the numbers of root knots caused by nematodes.The order of inhibitory activities of these fungi is as following,AO283 > PC > PE > AO282 > AO > AO281 > controls.According to the effects of promoting plant growth,PC > AO283> AO281 > AO282 = AO = PE > control.The combination of nematode pathogenic fungi with thermophilic fungus TD-treated soil demonstrated better anti-nematode effects than single use of TD.Among the tested fungi,PC and AO283 displayed the best inhibitory activities against nematodes.In addition,the physiochemical properties of compost soil treated with thermophilic fungus TD for 15 days and 30 days,respectively were evaluated.The contents of total phosphorus,total potassium,available potassium,available magnesium and available sodium in the soil significantly increased.The TD treated soils displayed significant effects on the growth increase of vegetable pakchoi.The fresh shoot weight of pakchoi planted in soil treated with TD for 15 days and 30 days increased by 72% and 122%,respectively.In summary,TD not only improved the soil fertility,but also reduced the plant root-knots induced by nematodes.It can also be used in combination with important normal-temperature nematode-pathogenic fungi to control nematodes.Preliminary study on the functions of two-P450 genes AOL_s00075g118 and AOL_s00078g25 in nematode-trapping fungus A.oligospora.These two genes were knocked out respectively.The ΔAOL_s00075g118 and ΔAOL_s00078g25 mutants displayed significant increases in conidia formation by 65.62% and 47.32% respectively,compared to wild-type strain,while showed no significant difference in mycelial growth and colony morphology.Mutant ΔAOL_s00075g118 displayed fast spore germination rate with 29.29% at 2 h and 17.22% at 4 h,respectively,higher than those of than wild-type strain.,while mutant ΔAOL_s00078g25 showed slow spore germination rates with at only 53.45% at 2 h and 66.67% at 4 h,respectively,of the wild-type strain.In addition,both mutants ΔAOL_s00075g118 and ΔAOL_s00078g25 displayed less trap formations and nematicidal abilities than wild-type strain.At 24 h,the number of ΔAOL_s00075g118 traps was 43.67% lower than that of the wild strains,the nematode mortality was only 58.14% of the wild strains,and the number of AOL_s00078g25 traps was 25.33% lower than that of the wild strains,and nematode mortality was higher than wild The strain decreased by 13.58%.HPLC metabolic analysis of the two mutant strains ΔAOL_s00075g118 and ΔAOL_s00078g25 displayed that there were 23 peaks changing in the HPLC profile of ΔAOL_s00075g118 and 20 peaks changing in that of ΔAOL_s00078g25.GC-MS profiles showed that there were 3 unique compounds 3-methyl-2-Butenal;2,6-dimethyl-2-Octanol and N,N,N’-trimethyl-N’-(4-piperidyl)-Ethylenediamine] detected in mutant ΔAOL_s00075g118,3 unique compounds in the wild strain,and 4 specific compounds 4-hydroxy-4-methyl-2-Pentanone;L-Homocitrulline;Benzaldehyde;1-Octen-3-ol in mutant ΔAOL_s00078g25,and 2 unique compounds in the wild strain.In general,the genes AOL_s00075g118 and AOL_s00078g25 were not only involved in sporulation,spore germination,trap formation and nematode capturing activities,but also in the metabolic profiles of nematode-trapping fungus A.oligospora.