Studies On Biological Characteristics、Epidemics Distribution And Spatial Distribution Of Corn Leaf Blight In Ya’an Region

Maize is the world and China’s major food, fodder, and industrial crop. However, the yield loss is more than50%on a regular basis due to the hazards of the maize leaf blight caused by Exserohilum turcicum, which occurs frequently in maize growing areas of China, resulting in an increasing threat to the safety of maize production and a direct impact on the sustainable development of maize. As the disease broke out in northern China, the current system reports related to the disease are mainly in North. From the point of view of disease epidemics, disease epidemic regularity can be influented widly,which based on the different climatic conditions and ecological environment that arising from regional differences, In order to take an effective prevention of corn leaf blight disease and reduce the impact of disease on corn yield, the of biological characteristics,corn leaf blight disease of time and space pop dynamic were studied in this research which based on the Ya’an special climatic conditions. This study was designed to understanding the biological characteristics of the,the epidemic regularity of disease, and the spatial distribution pattern.Then effectively make a stage division of the epidemic regularity and derive an optimum prevention and treatment period, to provide a theoretical basis for the local corn leaf blight disease forecasting. The main results of this test were as follows:1. The results of the study on Exserohilum turcicum’s biological characteristics showed that: Oats medium, PDA medium and PSA medium were the most suitable medium for mycelial’ growth, followed by PSA and corn leaf fried juice medium,PDA and corn leaf fried juice medium,the least suitable medium were corn leaf fried juice medium and Czapek medium.; mycelial could grow between10℃～35℃, and when the temperature was between25℃～35℃the mycelial grow quickly,28℃was the most appropriate temperature; the pH value of mycelial growth was not strict, the mycelium could grow between pH3～11, when the pH was7,the mycelial grow best; the different carbon sources has no much influence on mycelial growth,Relatively, the best carbon sources liked by pathogen were starch, sucrose and maltose,the lactose,glucose and xylose forrowed, fructose was the worst. The effective of nitrogen on mycelial growth was very abvious, Peptone, glycine and beef extract were the best, ammonium chloride and ammonium, sulfate were the worst. The effective of light on the mycelial’s growth was significant, The24hours continuous darkness and12h light12h dark alternating were more conducive to the growth of mycelium; the lethal temperature of mycelial was54℃(10min). The results of the study on Exserohilum turcicum conidia in Ya’an area show that: conidia could germinated in10～40℃, but germinated well at15℃～35℃, indicating that the conidia germinated well at medium temperature environment; In the pH value from3to12Conidia could germinate, the better was pH value2to11, and the most optimum pH value was8; Conidia germinate required high relative humidity, while the relative humidity (RH) was higher than75%conidia could germinate, and spores’germination rate increased as well as the humidity increasing; the conidia has good ability to resist high tempreture, the lethal temperature of conidia was53℃(10min);conidia germinated easily, stuy in different nutrient solutions, conidia germinated best in the water, and nutrition would inhibit the germination of conidia.2. The results of the study on epidemic dynamics of corn leaf blight disease in Ya’an area show that:at the same time, the corn leaf blight disease index of different maize varieties had certain differences, all varieties of corn leaf blight disease index increased with time, and the trend was obvious. Chuan Dan10,Chuan Dan28and Zheng Da2393were the fastest growth rate, Yu Dan19and Ya Yu24were the lowest growth rate. Due to humidity, temperature and other climatic conditions, the accumulation and expansion of lesions of corn leaf blight disease were not particularly obvious, and the disease index of all varieties were over45.The index of corn leaf blight disease in different times were simulation by SPSS18soft, LOGISTIC model that obtained by soft could reflect the popular dynamic of the disease over time. In addition, the composite model, the exponential model, S model could also reflect the trend of the disease over time. The infection rate of varieties corn leaf blight disease were significant different, between0.079to0.098, and infection rate of Chuan Dan28was highest.Disease period of Corn leaf blight in different maize varieties had some differences, Disease epidemics exponential growth of corn leaf blight in Ya’an region was more from corn emergence to late July, the Logistic period was ofen from late July to early September, the recession period was regularly from early September to the end of the maize growing season. The disease prevention and treatment time was deduced from the disease spot appearance to the middle of June. 3. The results of Spatial Distribution type research show that:by the trials between2010and2011, it could prove that In the whole process of com leaf blight disease occurred, the spatial distribution of com leaf blight disease of tested varieties maize on the Ya’an region were same, The analysis results showed that there was no significant difference in spatial distribution type of. corn leaf blight disease in a single growing season.By the Iwao optimum theoretical sampling model n=t2/D2×[(a+l)/X+β-1], the theoretical sampling number of com leaf blight disease in different disease severity were calculated,the results were as follows:in order to get a high accuracy in the test when the allowable error was0.1, under the conditions of1monoclonal lesion, at least2250strains of corn must be investigated, Even if the lesion number reached10,948strains of com need to investigated in order to ensure reliable results. If the survey data required only normal accuracy when the allowable error was0.2, then563strains of com must be investigated under the conditions of1monoclonal lesion, when the lesion number reached10, investigated more than250com plant was appropriate. If the test only need a rough survey data just when the allowable error come to0.3, guaranteeing a minimum survey of250can ensure the accuracy under the condition of1lesion. when the test plots were in serious condition with a high disease index,. the minimum investigation of106can insure accuracy when the lesion number reached10per strain.