Collaborative Research: Sudden Oak Death: Feedback Between a Generalist Pathogen, Hosts, and Heterogeneous Environments at Multiple Spatial and Temporal Scales

橡树猝死症（SOD）是由真菌样病原体多枝疫霉（Phytophthora ramorum）引起的，是一系列外来森林疾病中最新的一种，这些疾病包括板栗枯萎病和荷兰榆树病。在过去的10年里，加州和俄勒冈州沿海森林中可能有数百万棵橡树和橡树因SOD而死亡。该项目将研究最初导致多枝原枝孢出现的环境和生物条件以及随后与疾病相关的森林环境变化。本研究将结合田间、温室、室内实验，沿着利用地理资讯系统（GIS）及数学模拟等方法，研究SOD的时空动态。该项目将研究人类引起的景观结构和森林组成的变化如何与天气模式（例如，厄尔尼诺）可能影响了病原体在加州森林中的建立和传播。随着枝枯病菌的入侵，病原菌、寄主和森林环境也会发生变化。多枝假单胞菌（P. ramorum）是一种多面手病原体，感染超过45个属的植物，包括蕨类植物、裸子植物、单子叶植物和双子叶植物。加州森林中的SOD流行病主要是由这些作为病原体来源的相关宿主物种的存在驱动的，而不是由橡树本身驱动的。由于死亡率通常仅限于橡树和橡木，广泛的寄主范围的P. ramorum将允许我们测试假设的植物竞争介导的病原体。病原体的广泛宿主范围也可能允许多枝假单胞菌种群朝着增加的毒力和/或增加的多样性进化。然而，随着时间的推移，我们也可以预期，入侵P. ramorum将影响抗性和耐受宿主基因型的发生和空间分布。最后，寄生虫在影响生态系统功能方面的作用（例如，营养循环）往往被忽视。在与P. ramorum相关的上层死亡率显著影响沿海森林组成的地区，我们将分析森林地面输入，有机质，分解速率和氮动态的变化。 更好地了解入侵过程和影响的通用病原体是至关重要的管理和监管战略，以保护自然生态系统。 这项研究将在疾病政策和管理、公共宣传和教育方面产生广泛的影响。更好地了解入侵过程和影响的通用病原体是至关重要的管理和监管战略，以保护自然生态系统。PI积极参与向州、联邦（APHIS）和国际委员会提供关于SOD和其他森林疾病的咨询。多枝假单胞菌具有最广泛的宿主范围的任何真菌病原体曾经试图被隔离，并将作为一个模型，为未来的病原体引进的反应。 该项目还将支持4名研究生，3名博士后以及一些本科生的教育。每个实验室都有包括代表性不足的群体的历史。作为他们教育的一部分，博士后和研究生将参与公共宣传工作。将继续与北方加州的几个美洲土著部落（Pomo、Hoopa和Yurok）就SOD的研究和管理开展现有合作。

Sudden Oak Death (SOD), caused by the fungal-like pathogen Phytophthora ramorum, is the latest in a long line of exotic forest diseases that includes chestnut blight and Dutch elm disease. Potentially millions of tanoak and oak trees in coastal forests of California and Oregon have been lost to SOD over the past 10 years. This project will examine the environmental and biological circumstances that initially led to the emergence of P. ramorum and the subsequent disease-related changes to the forest environment. We will use a combination of field, greenhouse, and laboratory experiments along with geographical information system (GIS) and mathematical modeling approaches to research the spatial and temporal dynamics of SOD. The project will examine how human-induced changes in landscape structure and composition of forests when combined with weather patterns (e.g., El Nino) may have influenced the establishment and spread of pathogen in California forests. Following P. ramorum invasion, changes may also occur to the pathogen, host and forest environment. P. ramorum is a generalist pathogen that infects plants in over 45 genera including ferns, gymnosperms, monocots and dicots. SOD epidemics in California forests are primarily driven by the presence of these associated host species that serve as sources of the pathogen, and not by the oaks themselves. Because mortality is often restricted to oak and tanoak, the broad host range of P. ramorum will allow us to test hypotheses of plant competition mediated by a pathogen. The broad host range of the pathogen may also allow for P. ramorum populations to evolve towards increased virulence and/or increased diversity. However, over time we would also expect that invasion by P. ramorum will influence the occurrence and spatial distribution of resistant and tolerant host genotypes. Finally, the role of parasites in influencing ecosystem functioning (e.g., nutrient cycling) has often been overlooked. In areas where P. ramorum-associated overstory mortality has significantly impacted composition of coastal forests, we will analyze changes in forest floor inputs, organic matter, decomposition rates, and nitrogen dynamics. A better understanding of invasion processes and impacts of generalist pathogens is critical for developing management and regulatory strategies to protect natural ecosystems. This research will have a number of broad impacts in disease policy and management, publicoutreach, and education. A better understanding of invasion processes and impacts of generalist pathogens is critical for developing management and regulatory strategies to protect natural ecosystems. The PIs are actively involved with advising state, Federal (APHIS) and International committees on SOD and other forest diseases. P. ramorum has the broadest host range of any fungal pathogen ever attempted to be quarantined and will serve as a model for responses to future pathogen introductions. The project will also support the education of 4 graduate students, 3 post-docs as well as a number of undergraduate students. Each lab has a history of including under-represented groups. As part of their education, post-docs and graduate students will be involved in public outreach efforts. Pre-existing collaborations on research and management of SOD will be continued with several Native American tribes (Pomo, Hoopa, and Yurok) in Northern California.