| Digitaria sanguinalis is recognized as a malignant weed in the world.It has strong survival ability and wide distribution,which seriously endangers the production of autumn crops.E.sorghinum with strong pathogenicity was isolated from the diseased leaves of D.sanguinalis in the early stage of our laboratory.It not only has rapid pathogenicity to D.sanguinalis,but also has herbicidal activity.It is a potential weed biocontrol fungus.In this study,the biological characteristics of the biocontrol fungus such as culture conditions,sporulation conditions and spore germination conditions were studied,and the secondary metabolites were isolated,purified,identified and determined for biological activity.In terms of culture conditions,the weed biocontrol fungus grew rapidly on the seven tested media,and the colony diameter could reach 47-72 mm after 5 days.Among them,the growth rate was the fastest in D.sanguinalis medium,followed by PDA and carrot medium.Light conditions had no significant effect on the mycelial growth rate,but the mycelial thickness of the colony under dark conditions was significantly thicker than that under light conditions.The mycelium can grow normally at 15-30 °C,and grow fastest at25 °C.Treatment with 47 °C water bath for 10 min could kill the mycelium.The mycelium could grow normally in the pH range of 5-10,and there was no significant difference in growth rate.However,the back of the colony showed obvious red under alkaline conditions.The biocontrol fungus could not produce sporangia after 14 days of artificial culture.It was found that both mycelial scraping and UV irradiation could stimulate the production of sporangia.Compared with the alternation of light and dark,dark conditions are more conducive to the production of sporangia.The pH of the medium in the range of 5-10 had no significant effect on the yield of sporangia.After 7 days of culture on PDA medium,the mycelium scraping treatment + UV irradiation for 1h,placed at 25℃,dark conditions culture sporulation effect is best.In the water agar medium,25℃ dark culture conditions,conidia began to germinate after 4h,and the germination rate reached 81 % after 12 h.Temperature and medium pH had significant effects on spore germination,and the germination rate was the highest at 25℃.The germination rate of conidia decreased in the range of pH 5-10,that is,the acidic environment was more conducive to conidia germination.Ethyl acetate was used to extract the metabolites of the biocontrol fungus medium.The crude extracts were separated and purified by silica gel column chromatography and semipreparative high performance liquid chromatography,and a total of 6 components were obtained.Two compounds,epoxydon and(+)-gabosine Q,were identified by nuclear magnetic resonance and mass spectrometry.The herbicidal activity of the two compounds was determined by seed germination method and isolated leaf method.The results showed that Epoxydon had good herbicidal activity,and the inhibition concentration of seed germination was 737.5 mg/L.1000 mg/L Epoxydon aqueous solution could cause significant damage to the leaves of D.sanguinalis within 24 h.The sensitivity of 58 plants in 29 families to Epoxydon was further determined.All the tested plants could produce obvious damage within 72 hours after treatment,and the sensitivity of Poaceae and Asteraceae to Epoxydon was relatively high.In summary,through the study of the biological characteristics of E.sorghinum,it was found that it had a wide range of suitable growth,and a large number of sporangia could be obtained after induction,which had the basic conditions for the development of biological herbicides.A secondary metabolite component Epoxydon with herbicidal activity was isolated,which has high phytotoxicity and has the potential to be developed as a biological herbicide.This study has certain reference value for the study of biological and biological herbicides using E.sorghinum. |
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