Wu B M, Subbarao K V, van Bruggen A H C
Department of Plant Pathology, University of California, Davis, c/o United States Agricultural Research Station, Salinas, CA 93905.
Biological Farming Systems, Wageningen University and Research Centre, The Netherlands.
Plant Dis. 2005 Jan;89(1):90-96. doi: 10.1094/PD-89-0090.
Previous studies in coastal California suggested that morning leaf wetness duration and temperature immediately after the prolonged leaf wetness period affect infection of lettuce by the downy mildew pathogen, Bremia lactucae. In this study, spatial analysis tools in a geographic information system were used to interpolate disease assessment data and then relate them to weather variables measured in 1995 and 1997 at weather stations in the Salinas Valley. Among the variables monitored at these weather stations, midday temperature (10:00 A.M. to 2:00 P.M.) was related most strongly to the interpolated downy mildew incidence in a circular area (radius = 5 km) around each station (r = 0.52, P < 0.0001); the higher the midday temperature, the lower the disease incidence. High humidity and prolonged morning leaf wetness duration also were associated with high downy mildew incidence. Cluster analysis resulted in distinct regions with different midday temperatures, which overlapped well (92.2% of the total area) with regions distinguished in previous cluster analyses of downy mildew incidence. Clusters of morning relative humidity showed similar patterns, although they overlapped less well with clusters of disease incidence. These results confirmed that midday temperature is an important determining factor for lettuce downy mildew, and its effects should be incorporated into a disease warning system for coastal California. Cluster analyses based on the effects of temperature have great potential for use in regional downy mildew risk assessment.
此前在加利福尼亚州沿海地区开展的研究表明，早晨叶片湿润持续时间以及长时间叶片湿润期结束后的温度会影响霜霉病病原体（莴苣盘梗霉）对生菜的侵染。在本研究中，利用地理信息系统中的空间分析工具对病害评估数据进行插值，然后将其与1995年和1997年在萨利纳斯山谷气象站测得的气象变量相关联。在这些气象站监测的变量中，中午温度（上午10:00至下午2:00）与每个气象站周围圆形区域（半径 = 5公里）内插值得到的霜霉病发病率关联最为紧密（r = 0.52，P < 0.0001）；中午温度越高，病害发病率越低。高湿度和较长的早晨叶片湿润持续时间也与高霜霉病发病率相关。聚类分析产生了中午温度不同的不同区域，这些区域与先前对霜霉病发病率进行聚类分析所区分的区域有很好的重叠（占总面积的92.2%）。早晨相对湿度的聚类显示出类似的模式，尽管它们与病害发病率的聚类重叠程度较低。这些结果证实中午温度是生菜霜霉病的一个重要决定因素，其影响应纳入加利福尼亚州沿海地区的病害预警系统。基于温度影响的聚类分析在区域霜霉病风险评估中具有很大的应用潜力。
