Discovery Of Bioactive Substance Against Phytophthora From Natural Products

Phytophthora is a notorious kind of strong phytopathogenic oomycetes which causes the most devastating plant diseases in the world.It spreads rapidly,and has a wide range of host plant so that it causes serious damage to agricultural production and natural ecosystem.However,most of Phytophthora species produce serious resistance to many chemical fungicides on account of long-term and extensive application Therefore,the studies on searching for new anti-Phytophthora substance will contribute to prevention and control of plant diseaseSamples from natural products were screened for their inhibitory activity on sporangium formation of Phytopht.hora,and the EtOAc layer of methanol extract of Polygonum was found to have significant inhibitory activity.Guided by the bioassay,the EtOAc layer was chromtographed on silica gel and ODS,then purified by HPLC to afford five active compounds(1-5).In addition,five active compounds(6-10)were obtained from Kalimeris indica based on our previous study.The chemical structures of compounds 1-7 were determined by spectroscopic analysis(1H NMR、HRMS)and comparison of spectroscopic data with those reported.However,chemical structures of compounds 8-10 weren’t determined due to their amount,and they are probably triterpenoid saponins.Bioassay results indicated that compounds 1-10 showed remarkable inhibitory activity on sporangia formation of Phytophthora.Among them,Compound 3 showed the best inhibitory activity,the inhibition rate was 90%at a concentration of 3 μM,and it would reach to 100%when the concentration increased to 10 μM.On the other hand,more than 100 extracts of traditional Chinese medicine and marine organisms were screened by a bioassay system which could obtain active samples against hypha growth of Phytophthora,and extracts of Sophora flavescens,Acorus tatarinowii and Cnidium monnieri were found to be active samples.Guided by this bioassay system,one active compound was obtained from each extract after separation and purification.Then structures of compounds 11-13 were determined by spectroscopic analysis and comparison of spectroscopic data with those reported Bioassay results indicated that compounds 11-13 inhibited hypha growth of Phytophthora significantly,and compounds 11 and 13 has been reported to have the same activity.In our studies,thirteen active compounds were isolated from natural products guided by bioassay system.Compoundsl-10 and 11-13 show remarkable inhibitory activity on sporangia formation and hypha growth of Phytophthora,respectively.And these results will lay a foundation on the research of fungicides against Phytophthora.