Pacific Southwest Research Station, United States Department of Agriculture Forest Service, P.O. Box 245, Berkeley, CA 94701, USA.
Phytopathology. 2011 Apr;101(4):492-501. doi: 10.1094/PHYTO-03-10-0064.
The transmission ecology of Phytophthora ramorum from bay laurel (Umbellularia californica) leaves was compared between mixed-evergreen and redwood forest types throughout winter and summer disease cycles in central, coastal California. In a preliminary multisite study, we found that abscission rates of infected leaves were higher at mixed-evergreen sites. In addition, final infection counts were slightly higher at mixed-evergreen sites or not significantly different than at redwood sites, in part due to competition from other foliar pathogens at redwood sites. In a subsequent, detailed study of paired sites where P. ramorum was the main foliar pathogen, summer survival of P. ramorum in bay laurel leaves was lower in mixed-evergreen forest due to lower recovery from infected attached leaves and higher abscission rates of infected leaves. Onset of inoculum production and new infections of bay laurel leaves occurred later in mixed-evergreen forest. Mean inoculum levels in rainwater and final infection counts on leaves were higher in redwood forest. Based on these two studies, lower summer survival of reservoir inoculum in bay laurel leaves in mixed-evergreen forest may result in delayed onset of both inoculum production and new infections, leading to slower disease progress in the early rainy season compared with redwood forest. Although final infection counts also will depend on other foliar pathogens and disease history, in sites where P. ramorum is the main foliar pathogen, these transmission patterns suggest higher rates of disease spread in redwood forests during rainy seasons of short or average length.
从加利福尼亚州中部沿海地区的常绿混交林和红杉林两种森林类型在整个冬季和夏季疾病周期中，比较了美洲月桂（Umbellularia californica）叶片上美洲茶疫霉（Phytophthora ramorum）的传播生态。在一项初步的多地点研究中，我们发现感染叶片的脱落率在常绿混交林地点较高。此外，由于红杉林地点的其他叶部病原体的竞争，最终感染计数在常绿混交林地点略高或与红杉林地点无显著差异。在随后对以美洲茶疫霉为主要叶部病原体的配对地点的详细研究中，由于受感染的附着叶片恢复能力较低和感染叶片的脱落率较高，夏季美洲茶疫霉在美洲月桂叶片中的存活量在常绿混交林中较低。接种物产生和美洲月桂叶片新感染的开始时间在常绿混交林中较晚。红杉林中雨水和叶片上最终感染计数的平均接种物水平较高。基于这两项研究，在常绿混交林中，美洲月桂叶片中水库接种物的夏季存活率较低，可能导致接种物产生和新感染的开始时间延迟，与红杉林相比，在雨季早期疾病进展较慢。尽管最终的感染计数还将取决于其他叶部病原体和疾病史，但在以美洲茶疫霉为主要叶部病原体的地点，这些传播模式表明在短或平均长度的雨季中，红杉林的疾病传播速度更高。
