Epidemic And Forecasting Of Wheat Powdery Mildew In Ya’an

Although there have been so many reports on wheat powdery mildew, epidemic laws of wheat powdery mildew are distinct according to different geographical and climatic factors. Being a subtropical area with humid monsoon climate, Ya’an is also the transition zone between the Sichuan Basin and Qinghai-Tibet Plateau climate. Hereby, the pathogenesis, over-wintering and over-summering of wheat powdery mildew exhibit their inherent characteristics. This paper has targeted the wheat powdery mildew epidemiology in Ya’an with the following three parts:the observation of epidemic dynamics of two varieties susceptible to powdery mildew in Ya’an; over-summering of the wheat powdery mildew at different altitude and the volunteer wheat seedlings during the over-summering stage; the establishment of the forecast model of the disease based on all years’ investigation about the disease, further providing directions for the prevention and control of wheat powdery mildew. Based on the pathogenesis incidence of Chuanyu20and chuannong26in the whole growing season and the number of wheat powdery mildew spores in the air from2009to2011, it has showed that the seedlings in autumn were liable to be susceptible to be infected by powdery mildew from the late November to the middle of December, and then a two-month stage called bacteria source "preparation period",occurred with the significant growth diseased leaves rates but not obvious the growth of disease index, followed by a rapid growth of the disease index and this stage called "Outbreak period". The fungi could pull through the winter in the form of conidial morphology and keep to infect wheat occurring powdery mildew, until wheat maturity in early May. Analysis shows that, the exponential phase epidemic dynamics of Wheat Powdery Mildew in time(The rate of diseased leaves Less than5%) is changing with different years, But the logistic period(The rate of diseased leaves less than95%and more) relatively stable. Due to the different disease-resistant of varieties, the length of logistic phase are different, we can found that the length of logistic phase of Chuannong26is about15d short than chuanyu20through two years of observation data. Deal the relationship between the average disease index or diseased leaves rates of wheat powdery mildew and time with logistic curve analysis and S-curve analysis respectively, it was found that most of the array data could fitting curve logistic curve better. In which the average disease index of Chuanyu20could obtain excellent effect of fitting to logistic curve.The fitting rate of these two cycles could reach0.946and0.937respectively, the F-Statistic were314.595and251.887.The over-summering investigation of wheat powdery mildew relies mainly on the cultivation of the varieties susceptible to the powdery mildew wheat at the distinct altitudes, including Chuanyu20and Chuannong26in the Zhougong Mountain and the Pear Mountain in Ya’an. The paper also used the conidia and cleistothecia of wheat powdery mildew to infect the susceptible wheat seedlings and the summer-sown seedlings in the green-house, in combination with the daily observation of the summer-sown seedlings and volunteer wheat seedlings during the period of over-summering in the farm of Sichuan Agricultural Uniersity in Ya’an, and the same experiments in the Liantian Mountain in Yibin were made. Hereby, it has demonstrated that the conidia and the cleistothecium of wheat powdery mildew could successfully infect the wheat summer-sown seedlings at more than600meters above the sea level under the natural condition in Ya’an. According to the collected data about growth and morbidity of the wheat summer-sown seedlings from many towns and villages in2010, the observation could be obtained that under the appropriate circumstances, wheat powdery mildew could survive the summer in the form of grey brown harden morphology. However, in the artificial greenhouse, wheat powdery mildew was also able to successfully infect summer-sown seedlings by its cleistothecium or ascospores, and continues to infect the wheat seedling until the late November of that year with the final formation of cleistothecia.The forecast model was established based on four pathologic characteristics provided by the disease survey data and meteorological data in Ya’an from1990to2009. In accordance with the analysis and the confirmation, we had calculated seven convincing prediction equations, the precise ones were as follows:in the milk ripe stage, the disease field rate was described as Y=11.271+1.034X22,the average disease leaves rate was showed as Y=5.795+0.959X2, the average disease index was described as Y=1.5755+0.129X14-0.054X17+0.350X23, the morbidity area ratio was considered as Y=9.776-0.152X15+0.870X25,respectively. In the flowering stage, the disease field rate was described as Y=2.837+1.515X19, the disease index was deduced as Y=-0.015X6+0.004X9-0.020X15+0.252X19+1.4045, and the morbidity area ratio was considered as Y=-0.135X6-0.208X15+3.355X21+8.075. In these equations, X6,X15and X17represented the relative humidity anomaly in December of last year, January of this year, March of this year, respectively. X9showed the anomaly of rainfall, X14displayed the average temperature anomaly in April, X19appeared the anomaly of average disease field rate, X21revealed the anomaly of average disease index in early spring, X22stood for anomaly of average disease field rate in the flowering stage, X23presented the anomaly of the average disease leaves rate, X25reported the anomaly of morbidity area ratio in the flowering stage of wheat.