Studies On Epidemics And Spatial Distribution Of Maize Gray Leaf Spot In Ya’an Region

Maize is the most widely distributed crop around the world, but serious disease has become an important factor affecting corn production. In recent years, after following corn leaf blight and Curvularia leaf spot, Gray leaf spot of maize (Cercospora zeaemaydis Tehno and Dainels) emerged as another area of the outbreak of the corn leaf disease. The characteristics of the disease:Distribution range more widely than other diseases, and pathogen adaptability than other diseases. Gray leaf spot disease initially in the Americas and the African continent seriously, since1991the outbreak of the large area of Liaoning Province in China, and in recent years it has been gradually extended to a nationwide, and the trend is increasing. Since2008the disease occurred in a large area in Ya’an, Sichuan Province, and caused huge losses to the local corn industry development. Because of the disease broke out in northern China, so the current system related to the disease reported mainly in the north. From the point of view of disease epidemics, based on regional differences arising from different climatic conditions and ecological environment, disease epidemic regularity can be influented widly. In view of this point, the effective prevention and control of gray leaf spot disease, reduce the impact of disease on corn yield, this test the Ya’an special climatic conditions, from the gray leaf spot disease of time, space pop dynamic study designed to in-depth understandingthe occurrence of the disease epidemic law and the spatial distribution pattern, and accordingly do the derivation of Ya’an region of gray leaf spot disease division of the popular stage and the best disease prevention and treatment period, in order to provide a theoretical basis for the local gray leaf spot disease forecasting. The main results of this test are as follows: 1. The results of the study on epidemic dynamics of gray leaf spot disease in Ya’an area show that: at the same time the gray leaf spot disease index of different maize varieties have certain differences, all varieties of gray leaf spot disease index increase with time and growth, and the trend is obvious. Ya Yu12and Chuandan19are the fastest growth rate, the Provisional Austrian maize varieties slope of the curve than other varieties, indicating that from the beginning of the investigation of gray leaf spot pathogen of the species will continue to infect, Chuandan15early infection rate low, post-infection rate is rapidly increased, but the time was short duration. Due to humidity, temperature and other climatic conditions, the accumulation and expansion of the number of lesions of gray leaf spot disease is not particularly obvious, and the condition index of all varieties are over40.Different times of maize gray leaf spot disease in index by SPSS18software simulation obtained LOGISTIC model that best reflects the popular dynamic of the disease over time. In addition, the composite model, the exponential model, the growth model can to some extent, reflect the trend of the disease over time, but five varieties of maize gray leaf spot disease index increase with time change models. Different varieties of gray leaf spot disease infection rate changes are significant differences between0.114to0.207, which Chuandan19apparent infection rate.Gray leaf spot disease period of different maize varieties have some differences, Ya’an region in terms of the overall gray leaf spot disease epidemics exponential growth from corn emergence to early August, the the Logistic period from early August to early September, the recession period from9early May to the end of the maize growing season. Deduced that the disease prevention and treatment time in early July.2. Type of study results show that: by2010, the2011two-year trial, to prove that early in the gray leaf spot disease, the occurrence of disease peak and disease end of the tested varieties of maize spatial distribution on the Ya’an region of gray leaf spot disease space distributionThe analysis results are aggregated distribution. Description of a single growing season Neiya An area of gray leaf spot disease strain there was no significant difference in the type of spatial distribution. The lwao optimum theoretical sampling model n=t2/D2×[(a+l)/X+β-1]. calculate the2010and2011in Yaan maize gray leaf spot disease in different disease severity theoretical sampling number of results are as follows: If the test requirements of very high accuracy, then, at least under the conditions of a monoclonal lesion is a sample survey of3500corn, even if the lesion number reached500, gray leaf spot disease has a high degree of proliferation of the spread is still at least need to investigate400strains of corn in order to ensure reliable results. If the pilot requires only that the survey data is accurate, then the number of monoclonal lesions under the conditions of a about a sample survey of900corn for test plots disease widely disseminated in order to investigate more than100corn plant is appropriate. Only need a rough survey data, lesion number per plant is about one of the conditions, guarantee a minimum survey of400can ensure that the minimum investigation so that50when the test plots in serious condition, a high disease index can insure accuracy.