Pathogenicity And Disease Control Of Cell Wall Degrading Enzyme Of Phytophthora Infestans

Potato early blight is an important fungal disease in potato production, caused by Alternaria solani, and has lead to great economic losses to production areas of potato. In this paper, to provide theoretical basis for further study on molecular pathogenesis of pathogens and more effective chemical control, the pathogenic factors of potato early blight fungus and field chemical control are studied.1. Preparation by screening the production condition of cell wall degradation enzymes, potato early blight fungus was cultivated in liquid medium. The results showed that the potato early blight pathogen can produce some enzymes in improved Marcus liquid medium such as polygalacturonase(PG), pectin methylgalactuonase(PMG), cellulase(Cx) and β-glucosidase(βG), the activity of pectinase(PG, PMG) is higher than cellulase(Cx, βG). The optimal condition for culture of pectinase are found: initial p H 4.0, 30 ° C continuous shaking culture 3 ~ 4 d. For cellulose, initial p H 5.0, 25 ° C sustained oscillation 6 d.2. To explore the effect of pathogenic cell wall degradation enzymes on potatoes, the conductivity and reducing sugar of potato leaves dealt with enzyme liquid were determined. The results showed that the pectinase and cellulose cause different degrees of damage on cell membrane, cell membrane injury rate increases with the extension of processing time, and the pectinase damage rate on cell membrane is higher than cellulose. The content of reducing sugar treated with cellulose is more than that treated with pectinase.Cell wall degradation enzyme activity was determined in living tissue pathogen. The results showed that the activity of polygalacturonase(PG), pectin methylgalactuonase(PMG), cellulase(Cx) and β-glucosidase(βG) is significantly higher than CK, after resistant varieties infection certain period of time. After susceptible varieties were infected 12 h, the activity of pectinase and cellulose is up, and reach the peak; At first, the activity of pectinase and cellulose change little, after 60 h, it increases and reach the peak at 84 h. The activity of cellulose is significantly higher than pectinase. In this experiment, the role of Pectinase and cellulase in the pathogen infection are identified.3. The field experiments were carried out to study fungicide spraying time, number and mixed with foliar fertilizer application on the influence of early disease control effect and yield, and the test results showed that the mix of mancozeb and Azoxystrobin show great control effect. The above 85% control effect can be reached as followings: spraying the chemicals a week before or at diseases beginning period, 2 to 4 times during whole growth period. If spraying late or more than 3 times, the control effect or cost is not appropriate. Use of fungicide or foliar fertilization can reach 83.2% control effect, if use separately. But if mix use of fungicide and foliar fertilization, the control effect is not good as separate. In most mixtures, the yield can reach 41667.5 kg/hm2 and income are highest if mix use of fungicide and Kang Puhong, Kang Pulan or Shi Date.