Regions Of Oversummering Of Wheat Powdery Mildew In China

Blumeria graminis f.sp.tritici(Bgt),the pathogen that causes wheat powdery mildew,can oversummer as mycelia or conidia on volunteer wheats in cool mountainous areas in China.Oversummering is the most important stage in pathogen life history and infection cycle and it is the key stage for disease management.The researches of the key meteorological factors analysis,climate-based regional classification and the impact of global climate change on Bgt oversummering are important to wheat powdery mildew oversummering management and scientific disease forecasting.1.Correlation analysis of oversummering and the meteorological factors of wheat powdery mildew In this study,the average and the maximum of the hottest ten-days' temperature,the mean values of precipitation,wind velocity,relative humidity and sunshine duration from July to August during 1951~2013 of 752 meteorological stations were analyzed and spatial interpolation.The meteorological data(the highest temperature,the average temperature,the average precipitation,the average relative humidity,the average relative humidity and the average sunshine duration)of 194 Bgt investigation points were obtained afterwards.The correlation analysis between meteorological factors and the oversummering probability shows that the oversummering probability has a very significant correlation withthe average and the highest temperature,but has no significant correlation with other meteorological factors.Therefore,the temperature is the key factor for wheat powdery mildew oversummering.The results provided the theoretical basis for the temperature-based evaluation of the wheat powdery mildew oversummering region classification.2.The oversummering region classification of wheat powdery mildew In view of the deficiency of the previous researches,we improve the classification method as followings.On one hand,considering the relationship between temperature and altitude,longitude,latitude,and the difference between the years,the regression equation fitting the the hottest ten-days' mean temperature,altitude,longitude,and latitude.On the other hand,the effect of elevation on spatial interpolation is considered and the resolution is improved to 20 km.The oversummering distribution maps of wheat powdery mildew with terminate threshold value 25.53? and 26.24? were drawn,separately.Through the oversummering point test,the coincidence rate was 100% for the 26.24? average termination threshold and 93.71% for the 25.53? one.The results showed the oversummering region classification based on 26.24? average termination threshold was more reliable than 25.53?.Moreover,the coincidence rate for the 25.53? average termination threshold in this study was also higher than the previous ones.Results showed that wheat powdery mildew in China,the summer range mainly concentrated in North Central Yunnan,central Sichuan,West Guizhou,Southeast Gansu,Southeast Ningxia,North Central Shaanxi,west Henan,Central Shanxi,West Hebei et al.,formed a north-south main oversummering belt.3.Effects of global warming on wheat powdery mildew oversummering stage Through analysis of historical and forecast data of Chinese climate warming,the long-term trend of the average temperature growth rate of the wheat powdery mildew oversummering in China is about 0.25? increment every ten years,and the oversummering termination threshold decreased 0.45? every ten years.The oversummering prediction maps of wheat powdery mildew in 2030,2050 and 2100 were made based on the previously supposition.The prediction results showed that the oversummering termination threshold will increased to 26.64? and the oversummering region will expand to the southern northwest,southwest and central China regions by 2030,and will has an important influence on the occurrence and prevalence of wheat powdery mildew.By 2050,the oversummering termination threshold will increased to 27.04? and the oversummering region will expand to central,eastern and southern China,the risk of widespread wheat powdery mildew epidemic will be further increased.All winter wheat growing areas in China can complete oversummering by 2100 and the oversummering termination threshold will increased to 28.04?,severe wheat powdery mildew epidemic will occurred every year unless effective control mengment applied.Taking into account the adaptability of Bgt is limited,so it is assumed that can only occur in extreme cases by 2100.