Study On Related Pathogenic Factor And Infection Process Of Foxtail Millet Downy Mildew

Downy mildew caused by Sclerospora graminicola is an economically important disease affecting foxtail millet production. It causes huge losses every year in China. In some areas, the incidence rate is 42%. While, there is not much understanding about the pathogen. In this study, the materials was susceptible varieties Jingu 21, by means of microscope and scanning-transmission electron microscope, we wanted to track the infection process of pathogens. Secondly, we measured the change of cell wall degrading enzyme activity of infected leaves by DNS method. And we aslo did some analysis of microbial population diversity on the infected leaves. The main findings are as follows:1. We did continuous observation about pathogen infection process with paraffin method and ultrathin sectioning method. It found that pathogens through stomata cells went into the mesophyll cells. Through the cell wall and cell membrane they infected other heathy cells, and propagated. Eventually, the mesophyll cells of leaf broke down, except bundle sheath cells. "The hair" phenomenon was formed, leaves had diastema.2. We measured cell wall degrading enzyme activity change of different disease severity of infected leaves. The PG, PMG, PGTE activity of infected leaves rised when the severity went up. And they were significantly higher than the activity of Cx. In this process, the activity of CK had little change. The highest PGTE activity of infected leaves was 282.46U/g,177.74U/g higher than CK activity and 277.68U/g than Cx. The highest activity of PMG was 170.19U/g,167.00U/g higher than CK activity and 147.43U/g than Cx. The results were that pectinase was more important than cellulose. There, the lower position of leaves was, the more severe the infection was.3. With separation of other bacteria on the infected leaves and identification of it’s ITS sequence, there were deuteromycetes, ascomycetes and fusarium on leaves. The fungi 1,4,5 belonged to hyphomycetes and coelomycetes which included many important plant pathogens. After analysis of microbial population diversity, ascomycetes and basidiomycete were mainly fungi on the infected leaves, especially ascomycetes most. It ccounted for 88%-92%. In it, the population abundance of sordariomycetes-dypocreales-nectriaceae was highest. The fungi 2 was this kind of fungi. Dothideomycetes-pleosporales-pleosporaceae-alternaria aslo occupied a certain proportion. It was same as the phenomenon of chapter two. We thought these pathogens and downy mildew may had correlated.In summary, we have a certain understanding about the pathogen infection process, pathogenic factors and microbial population diversity. It lays the foundation for exploring the pathogenic mechanisms of downy mildew caused by Sclerospora graminicola.