Study On Pathotoxin From Pseudocercospora Oxalidis

Currently the control of Oxalis corymbosa DC prodr relies mainly on chemical methods. Although chemical herbicides have played a great role in solving theglobal food crisis,they have also polluted the ecological environment,caused deterioration of environmental quality and threatened the health of human beings.On the other hand,the increasing of the population of resistant weed and the appearance of anti-chemical-weed-killer weed has become an irrefragable problem.Study of controlling Oxalis corymbosa DC prodr by using biological controlling pathogen just gets to start,however it is one of the most potential fields for research because of its advantages: safer,lasting longer and less devotion.Through investigation we found that there,were different degrees of leaf spot on Oxalis corymbosa DC prodr in many places of Chongqing,and in some urban areas it was extremely serious,which might cause the losing plant of Oxalis corymbosa DC prodr.Studies show that the pathogen which caused leaf spot on Oxalis corymbosa DC prodr is Pseudocercospora oxalidis Gob & Hsieh,belonging to Deuteromycotina,about which there is little introductory literature presently.In this article the research content on the fungi and its pathogenic factors includes five parts. Firstly,filtrating strong pathogenicity strains in Chongqing Area was conducted.Secondly,inducing the filtrated ones to produce toxin,and testing the biological activity to make sure whether the toxin was the main pathogenic factor.The third part tried to explore the conditions and methods for extracting the toxin from Pseudocercospora oxalidis.The fourth was to do some preliminary analysis of the chemical nature of the toxin from Pseudocercospora oxalidis.Finally,the work was to test the stability of the toxin and to measue the biological activity on the main crops.During the leaf-spot period of Oxalis corymbosa DC prodr,81 strains were sampled in every area of Chongqing,which were necessity in the study.According to the state of seriousness grading standards and the virulence differentiation standards,the test of the pathogenicity of the 90-strains showed that their virulence had obvious difference,which presented in two aspects:on one hand, strains from different areas had different pathogenicity.Most of the strains taken from Beibei District, Shapingba District,Hechuan City and Wanzhou City had strong virulence,while most of those taken from Jiulongpo District and Rongchang City had weak virulence.On the other,strains from the same area might also have difference on pathogenicity.Among the 23 strains taken from Shapingba District 12 had strong virulence,which was more than one half of strains.While only two had weak virulence(YH-008-02,YH-028-01).The study indicated that Pseudocercospora oxalidis Goh & Hsieh could produce pathotoxin by in vitro cultivation.Bioassay results of the study indicated that the Pseudocercospora oxalidis Gob & Hsieh could produce pathotoxin on media.Toxins from the fungi had toxicity on the leaves of Oxalis corymbosa DC,and it was found the toxicity was concerned to the concentration of pathotoxin.The experiments of toxin-producing capability of the fungi under different environmental cultural condition were carried out.The optimal cultural conditions for the production of phytotoxin produced by Pseudocercospora oxalidis were temperature 25℃,pH6,and cultured period 15-18days. Furthermore,the production of phytotoxin favored darkness and enough swing of the ferment liquid.In the research three methods were used to extract the pathotoxin from Pseudocercospora oxalidis.The results showed that the ammonium sulfate precipitation was suitable for extraction of the toxin from the fungi and 90%of ammonium sulfate was the best for extraction of the toxin.This toxin chemical compound had higher polarity and was a macormolecule chemical compound.The primary analysis results of chemistry for the pathotoxin indicated that this pathotoxin was a macromolecule chemical compound,and this result was same to that of organic solvent extract.The survey on the content of protein and soluble sugar of the toxin showed that the content of protein and soluble sugar were 137.2μg/mL and 20.52μg/mL,respectively.The pathotoxin of Pseudocercospora oxalidis was detected to be a kind of glycoprotein,and its main component was protein.The research also focused on the host range of the pathotoxin of Pseudocercospora oxalidis.The results showed that tomato and bean were lightly susceptible to the pathotoxin,the other experimental crops showed no susceptibility.It suggested Pseudocercospora oxalidis was safe to the main crops.Research showed that the toxin usually had a higher thermal stability,and the toxicity wasn't affected by the pH among 4.0 and 11.0.Therefore the possibility that the toxicity of toxin-contained filtrate is caused by the acidity of liquor can be excluded.