Herbicidal Activity Screening Of Weed Pathogenic Fungi And Active Secondary Metabolites Of Strain SSQB01

Weeds in the field seriously affect crop yield and quality,increasing production costs.How to control weeds with high efficiency and low toxicity is one of the main problems that restrict the development of agriculture in China for a long time.Novel biopesticides of pathogenic fungal toxin origin to replace chemical herbicides are currently a major research hit in the field of weed control research.This paper mainly studies the herbicidal activity of their metabolites from weed pathogenic fungi,laying the foundation for the subsequent development of bio-derived herbicides.Weed pathogenic fungi were isolated and purified from pathogenic weeds,and the fermentation broth of the pathogenic fungi was obtained by liquid fermentation culture to test their inhibitory activity against Echinochloa crusgalli roots.The strains with good weed control activity were screened and selected.And the secondary metabolites of the target fungus were isolated and identified by combining silicone column chromatography,thin layer chromatography（TLC）,gel column chromatography,liquid chromatography and nuclear magnetic resonance.A total of 20 strains with good herbicidal activity were screened,and a total of 9 compounds were isolated from Bipolaris oryzae SSQB01,8 of which were identified and the herbicidal activity of the monomeric compounds was tested.The specific results are described below:1.52 weed pathogenic fungi were isolated and purified from pathogenic weeds,and the activity test results showed that ZBZJ-4（host:Eleusine indica）,ZBZJ-8（Alternanthera philoxeroides）,ZBZJ-11（Polygonum hydropiper）,ZBZJ-14（Phytolacca acinosa）,SSQB01（Paspalum paspaloides）,ZBZJ-27（Coix chinensis Tod）,ZBZJ-29（Cirsium arvense var.integrifolium）,ZBZJ-31（Solanum nigrum）,ZBZJ-36（mperata cylindrica）,ZBZJ-37（Acalypha australis）,ZBZJ-41（Rosa multiflora Thunb）,and ZBZJ-43（Bidens pilosa）showed strong inhibitory activity against E.crusgalli roots with 100%inhibition.ZBZJ-40（Rubus idaeus）and ZBZJ-3（Bidens pilosa）also showed strong inhibitory activity against E.crusgalli roots with the inhibition rate of 92%and 90%,respectively.6 strains of pathogenic fungi showed high inhibitory activity against E.crusgalli roots,with the inhibition rate of70-88%.The remaining 32 pathogenic fungi showed poor inhibitory activity against E.crusgalli roots,and the inhibition rates were less than 66%.2.Twenty strains with good activity and nine strains with rich metabolites were identified by its sequencing.The results showed that 15 strains of Alternaria（51.7%）,5 strains of Fusarium（17.2%）and 4 strains of Nigrospora（13.7%）,had high abundance.The other two strains belonged to Curvularia,one belonged to Phoma and one belonged to Bipolaris,One belongs to Botryosphaeria.Because of the good activity and abundant metabolites,the pathogenic fungus Bipolaris oryzae SSQB01 isolated from B.bipolaris,was selected as the target strain for further study.3.The metabolites of the target strain Bipolaris oryzae SSQB01 were isolated and identified.9 compounds were isolated and 8 of them were identified,namely,3-anhydro-ophiobolin A（1）,3-anhydro-6-epi-ophiobolin A（2）,ophiobolin A（3）,anhydrocochlioquinone A（4）,cochlioquinone A（5）,cochlioquinone B（6）,isocochlioquinone A（7）,mannitol（8）.4.The herbicide activity of the monomeric compound was tested.The results showed that,compound 1-2,3,5 showed strong inhibitory activity at the test concentration of 100μg/ml.Their inhibitory activities on E.crusgalli roots were 100%,and their inhibitory activities on Amaranthus retroflexus roots were 80.15%,81.38%,77.15%and 84.17%,respectively.The cytotoxic activity of compound 4 on cancer cells was further tested.It was found that it had medium cytotoxic activity on A-375（human melanoma tumor cells）,SKOV-3（human ovarian cancer cells）and MGC-803（human gastric cancer cells）with the IC₅₀ values of15.55,29.41 and 18.12μM,respectively.However,it is highly toxic to human normal hepatocyte L-02(IC₅₀=15.55μM)The above findings indicate that weed pathogenic fungi have good herbicidal activity and are an important resource pool of natural products of herbicidal activity.As a source of new herbicidal activity,they have important research value.