| As a large agricultural production country,the quality and yield of crops are currently a concerned issue.Weeds and crop diseases cause significant yield loss in global crop production.The extensive use of pesticides has caused a series of problems such as serious environmental pollution,food safety hazards and increased pathogen resistance.However,use of plant own allelopathy and resistance to control weeds and crop diseases can achieve the reduction of pesticides and the sustainable development of the agricultural environment.Rice is one of the main food products.Weeds and diseases are the main reasons for rice yield reduction.Investigation of the allelopathic effects of rice and corresponding allelochemicals has become a research hotspot in the field of allelopathy.There are many kinds of allelochemicals in rice hulls,which could be used as natural herbicides and bactericides.In this paper,weeds were used as experimental plants to evaluate the herbicidal activity of the techloroform,ethyl acetate and aqueous extracts of the product got after the rice hulls shad been treated reflux with the ethanol.Allelochemicals of chloroform and ethyl acetate extracts above were isolated and purified further by silicagel,MCI,C-18,Sephadex LH-20 and preparation liquid chromatography,and the structures were determined on the basis of nuclear magnetic resonance spectroscopy and mass spectrometry.The herbicidal and bacteriostatic activity of the isolates were evaluated.The chloroform,ethyl acetate and aqueous phase extracts of the product got after the rice cellhull sheed been treated under the low temperature reflux with ethanol could inhibit the growth of Echinochloa crusgalli.Among them,the chloroform extract and the ethyl acetate extract showed better inhibitory activities against Echinochloa crusgalli.The Chloroform extract could not ably inhibit the root and shoot growth of E.crusgalli,the root length and seedling were inhibited by 81.1% and 57.0%,respectively,at a concentration of 5 mg/mL.13 compounds were isolated from chloroform and ethyl acetate extracts by column chromatography,thin layer chromatography,preparative liquid chromatography,and the structures were identified due to NMR and MS.The structures of isolates were elucidated as momilactone A(1),momilactone B(2),tricin 4'-O-((7''S,8''S)-guaiacylglyceryl)ether(3),tricin4'-O-((7''R,8''R)-guaiacylglyceryl)ether(4),tricin(5),tricin-7-O-neohesperidoside(6),Stigmast-4,22E-dien-6?-ol-3-one(7),Stigmast-4-en-6?-ol-3-one(8),stigmasterol(9),?-sitosterol(10),vanillin(11),4-hydroxy-3-methoxycinnamaldehyde(12),4-hydroxycinnamic acid(13)The bioactivities of compounds 1-8 against E.crusgalli were evaluated.The results showed that all the compounds significantly inhibited the E.crusgalli seedlings.Among them,momilactone B showed the highest inhibitory effect.Bomilactone B E.crusgalli inhibited germination at a concentration of 20 ?g/mL.The bioactivities of compounds 1-8 on E.crusgalli were evaluated had similar inhibitory effects when the concentration was 100 ?g/mL,their inhibition rates against root length and seedling height of E.crusgalli were between 96% and 67%.Compounds 1-8 were tested for their antifungal activities against Magnaporthe oryzae,Fusarium oxysporum cubense,Fusarium oxysporum,and Fusarium graminearum.Among them,the MIC value of momilactone A for four fungi was 18.7 ?g/mL.The MIC value of momilactone A(1)for rice blast fungus(Magnaporthe grisea)was as low as 12.5 ?g/mL,and the MIC value of momilactone B(2)was 6.25 ?g/mL.Compound 8 had MCI value of 12.5 ?g/mL for Fusarium oxysporum cubense.MCI value of compounds 5 and 6 for Fusarium oxysporum cubense are 25.0 ?g/mL. |
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