Infection Simulation,Pathogenesis Mechanism Of Pseudoperonospora Cubensis And Induced Resistance By High Temperature In Cucumber

Cucumber downy mildew,caused by Pseudoperonospora cubensis Rostow,is a major disease of cucumber. The disease is severe in more 70 countries,causing considerable reduction in yield and quality. After 80s of 20th century,with the development of green house scale,the condition of temperature and humidity benefits to disease epidemic in green house,cucumber downy mildew is expanding which becomes the disturbance of cucumber production. In order to effectively control cucumber downy mildew and reduce pollution of the environment caused by chemical control,for ecological control of cucumber downy mildew we made following works.By the research of infection simulation of P. cubensis in cucumber,we identified the optimum temperature and humidity and studied the pathogenicity of P. cubensis under extreme temperature and humidity. As a result,the optimum temperature on the excised leaf of cucumber for infection was 25-35,successful infection required 2 hours of leaf wetness after inoculation. The P. cubensis which was preserved in -20 refrigerator for 10 mouths still keeps virulence. This result riches the former fruit. At the same time,we identified that relationship between temperature and pathogenicity described by Logistic model. The cucumber leaves in vitro and vivo can continuously produce sporangia. The relationship between days of symptom appearance and accumulation number of sporangium was described by a parabolic model. And relationship between days after symptom appearance and lesion area coincide to Gompertz model.We first reported that the pathogenicity mechanism of P. cubensis was the action of zymin and pathotoxins and extracted pathotoxin. Among pathotoxins,the component-SM-2,shows high activity.By studying both P. cubensis and cucumber treated by high temperature,we find induced resistance on cucumber downy mildew can be generated while P. cubensis is treated for 2 hours by 45 under R.H. 80%. And high temperature induced cucumber to resist cucumber downy mildew which is a creative thinking in this research. Studying on induced resistant mechanism,we find several resistant enzyme.for example PAL,POD,SOD,Chitinase and P -1,3-glucanase,shows higher activity than control. And cell wall surface deposited massive lignin. According to several factors,we think host defenseenzymes coordinate with lignin to resist infection of P. cubensis. However,Chitinase and 3 -1,3-glucanase decomposed sporangial cell wall,disrupted fungi tissue to express resistant action.On the whole,this research came up with theoretical fundament for control cucumber downy mildew by ecological control. Especially,it is creatively proposed that high temperature stimulates host to produce induced resistance,which can be used to control cucumber downy mildew in practice.Name: Shi YanxiaSpecialty: Plant Pathology Advisor: Liu Xuemin...