Study On Screening Of Agricultural Bioactivity Of Marine-Derived Fungi And The Secondary Metabolites Of Fusarium Equiseti D39

China is a big agricultural country with huge economic losses caused by serious plant diseases and weeds towards agricultural production annually.Although traditional chemical pesticides alleviate the losses to a certain extent,their unreasonable use has brought a series of problems,such as pesticide residues,environmental pollution and pathogen resistance.Therefore,biopesticides with low residue and high efficiency have become the focus of research and development.Marine fungi can produce secondary metabolites with novel structures and interesting bioactivities endowed by the unique marine environment,which is high pressure,high salinity,low temperature and oligotrophic environment.Many compounds have agricultural biological activities.This study mainly includes the following contents:1.In this study,138 fungal strains were isolated from marine annimals,plants,from which 47 independent strains were identified by morphological and molecular biological methods.Penicillium sp.,Aspergillus sp.,Fusarium sp.and Trichoderma sp.were dominant populations.The bioactivities of crude extracts against plant pathogens were tested by agar diffusion method and growth rate method.The phytotoxicity of 38 crude extracts against plant pathogens were determined by seed germination inhibition method and stem and leaf treatment method.The results showed that D27 has strong inhibitory effects on Alternaria brassicicola,Aspergillus niger,Diaporthe medusaea and Pseudopestalotiopsis theae.D1,D21 and D39 has strong antibacterial effect on the bacterium of Acidovorax avenae subsp.citrulli,Clavibater michiganensis subsp.michiganensis and Pseudomonas syringae pv.lachrymans.D1,D2,D3,D5 and D39 have an inhibitory effect on the rhizome growth or stems and leaves of amaranth.2.Based on the bioactive and chemical screening,a Fusarium equiseti D39 strain,which showed prominent bioactivities and contained abundant secondary metabolites were selected for further investigation.Fifteen compounds(1–15)were isolated by the column chromatography on silica gel,Sephadex LH-20 and semi-preparative reversed phase HPLC,and identified by spectroscopy of NMR,MS,IR,UV,ECD,VCD and X-ray diffraction.These secondary metabolites include six 3-decalinoyltetramic acids,two anthraquinones,three aliphatic compounds,three steroids compounds and one nucleotide.Among them,fusarisetin C(1),fusarisetin D(2)and anthraquinone A(7)are new compounds.Indeed,compound 2 represents the first 3-decalinoyltetramic acid,possessing an unprecedented carbon skeleton with a tetracyclic ring system comprising a decalin moiety(6/6)and a bicyclic moiety(5/5),according to the reported,the biosynthetic pathway was speculated.Equisetin(5),epi-equisetin(6),7 and anthraquinone B(8)exhibited potent antimicrobial activity,caused by the destruction of cell walls and membranes,the contents of the cell leak and cause cell death.In addition,compounds 5 and 6 also showed significant inhibitory effects on the germination of amaranth and lettuce seeds.The results showed that potato liquid medium with 1% salinity is the most favorable for the production of compounds 5 by OSMAC.The agricultural biological activities of marine-derived fungi were explored in this study.The secondary metabolites of marine-derived bioactivities fungi D39 were evaluated by using bioactivity models such as antimicrobial and herbicide.The mechanism of antimicrobial activity and fermentation conditions were preliminarily investigated.The application scope of marine natural products was broadened and the basis for the research and development of biological pesticides was provided.