| Maize is one of four major crops in China, and has remarkable economic and social benefits. Maize diseases have been main limited factor to production, of which northern leaf blight, gray leaf spot, and corn sheath blight are the major leaf diseases in corn production in Liaoning Province, because of the occurrence and harm of the diseases with a rising trend year by year, they cause great yield loss to maize production. With the development of new cultivation patterns and conservation tillage technology, the yield potential of maize population has been increased, and also the epidemics of maize diseases have been affected. In order to clear the occurrence dynamics northern leaf blight, gray leaf spot, and corn sheath blight in different ecological region, in this paper the occurrence and epidemic dynamics of the above diseases were investigated and monitored, combining with the field plot experiment, the epidemic regularity and constructed the dynamic and forecasting model of epidemic time of maize leaf diseases were defined. The effect of new cultivation patterns on epidemic dynamics of northern leaf blight and gray leaf spot and used the degree of ageing of leaves as morphological index for premature senescence. On this basis, the influence degree of maize leaf senescence, premature senility of maize and yield traits was cleared. The main results are as follows:1 The important component of epidemic process of northern leaf blight and gray leaf spot was analyzed by applying quantitative epidemiology. According to the results of laboratory test and field plot experiment, the quantitative relation between the five components (conidia germination, infection probability, spot expansion, sporulation and spores flying) of infection process of northern leaf blight and gray leaf spot and the three components (overwintering place, overwintering pathway and spread of diseases) of infection cycle were cleared and the effect of environmental factors on the main component of epidemic process of northern leaf blight and gray leaf spot, which laid previous foundation for studying on epidemic dynamics of northern leaf blight and gray leaf spot.2. The system monitoring of occurrence dynamics of the leaf diseases in different ecological region was carried out. From investigating, northern leaf blight, gray leaf spot, and corn sheath blight had become the main diseases which limited the production of corn. The three kind of maize diseases occurred in different region in Liaoning Province, but epidemic degree there were significant differences of occurrence and epidemic degree in different year and different area. For instance, northern leaf blight occurred seriously in cool area, such as Shenyang, Jinzhou and Tieling, gray leaf spot in Shenyang, Dandong and Dalian-humid area occurred seriously, and the trend of the occurrence of corn sheath blight in eastern and southern Liaoning province has changed into each region in Liaoning.3. The temporal dynamic and predictive models of maize leaf diseases under naturally infected condition were first constructed. According to field experiment, making analysis and comparison via SPSS11.5, logistic model was confirmed as the best one and respectively constructed six epidemic time and predictive models of three kinds of maize leaf diseases.(1) Temporal dynamic model of northern leaf blight:Y=1/(4.2735×10-3+400.0084exp(-0.1334t));(2) Multiple meteorological factors forecasting model of northern leaf blight:Y=1/ (4.4115×10-4+(0.0614exp(0.1253t-0.2159x1-0.0052x2-0.0079x3)));(3) Temporal dynamic model of gray leaf spot:Y=1/(7.8137×1015+0.0018exp(-0.3435t));(4) Multiple meteorological factors forecasting model of gray leaf spot:Y=1/(0.0018+5.1956×1011 exp(0.2498t+0.0687x1+0.0122x2+0.0090x3)));(5) Temporal dynamic model of corn sheath blight:Y=1/(0.0125+29.4358exp(-0.0664t));(6) Multiple meteorological factors forecasting model of corn sheath blight:Y=1/(0.0100+(0.0614exp(0.1253t-0.2159x1-0.0052x2-0.0079x3))).4. Impulsive logistic model with periodicity was first established. The model described epidemic dynamics of corn sheath blight among years. Impulsive logistic model with periodicity could more intuitively and definitely reflect the simulation on epidemics of corn sheath blight than logistic model among years, and also accorded to its biological significance. According to the impulsive logistic model, there were great differences in the max disease index among years, but there was little difference in the apparent infection rates. Logistic model deduced that exponential phase of corn sheath blight was from seeding stage to beginning July in Shenyang, the logistic phase was from beginning July to late August or early September, the decline phase was late August or early September to the end of corn grow stage.5. The epidemic temporal dynamic of northern leaf blight and gray leaf spot in new cultivation patterns were systematic studied in this paper. No-till with straw cover (NTSC), flat planting (FP), and wide-narrow row (WNR) changed plant spatial distribution, and also changed corn farmland ecosystem, and then significantly affect the epidemic dynamic of northern leaf blight and gray leaf spot. Through comparing and analyzing, Logistic model can well reflect the temporal dynamic of maize northern leaf blight and gray leaf spot in field by naturai infection. The exponential phases were different with different cultivation patterns. The sequence was NTSC, FP, CTM and WNR. The exponential phases were in order of CT, FP, NTSC, and WNR.The phase was also the best time to chemical control.6. Epidemic dynamic of northern leaf blight among different cultivation densities and sowing dates were definited. The disease severity among different cultivation densities were in sequence of 45000 plants/hm2>60000 plants/hm2>90000 plants/hm2>75000 plants/hm2, rational close planting was beneficial to control epidemic of northern leaf blight. Sowing date significantly affect epidemic of northern leaf blight. Early sowing in good time was significantly beneficial to the disease control and yield increase. Logistic model can well reflect the temporal dynamic of maize northern leaf blight among different cultivation densities and sowing dates by comparison analysis, deduced the different epidemic phases, and provided theoretical basis for the integrated control of northern leaf blight.7. Degree of whole maize leaf senescence was used as morphological index of maize senescence evaluation system by comparison analysis, and established classification standard of maize leaf senescence. Maize diseases obviously intensified maize senescence using artificial inoculation method. The influence degrees on maize senescence were in sequence of corn sheath blight, northern leaf blight, gray leaf spot, Curvalaria leaf spot. With the inoculation time delayed, the degree on maize senescence was gradually decreased.100-seed weight was decreased significantly after maize senescence, but ear diameter and kernel rows had no significant effects. |
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