A new canker disease, commonly known as sudden oak death, of Lithocarpus densiflorus, Quercus agrifolia, Q. kelloggii, and Q. parvula var. shrevei in California is shown to be caused by Phytophthora ramorum. The pathogen is a recently described species that previously was known only from Germany and the Netherlands on Rhododendron spp. and a Viburnum sp. This disease has reached epidemic proportions in forests along approximately 300 km of the central coast of California. The most consistent and diagnostic symptoms on trees are cankers that develop before foliage symptoms become evident. Cankers have brown or black discolored outer bark and seep dark red sap. Cankers occur on the trunk at the root crown up to 20 m above the ground, but do not enlarge below the soil line into the roots. Individual cankers are delimited by thin black lines in the inner bark and can be over 2 m in length. In L. densiflorus saplings, P. ramorum was isolated from branches as small as 5 mm in diameter. L. densiflorus and Q. agrifolia were inoculated with P. ramorum in the field and greenhouse, and symptoms similar to those of naturally infected trees developed. The pathogen was reisolated from the inoculated plants, which confirmed pathogenicity.

Phytophthora ramorum, causal agent of sudden oak death, is an emerging plant pathogen first observed in North America associated with mortality of tanoak (Lithocarpus densiflorus) and coast live oak (Quercus agrifolia) in coastal forests of California during the mid-1990s. The pathogen is now known to occur in North America and Europe and have a host range of over 40 plant genera. Sudden oak death has become an example of unintended linkages between the horticultural industry and potential impacts on forest ecosystems. This paper examines the biology and ecology of P. ramorum in California and Oregon forests as well discussing research on the pathogen in a broader management context.

Although healthy plants are vital to human and animal health, plant health is often overlooked in the One Health literature. Plants provide over 80% of the food consumed by humans and are the primary source of nutrition for livestock. However, plant diseases and pests often threaten the availability and safety of plants for human and animal consumption. Global yield losses of important staple crops can range up to 30% and hundreds of billions of dollars in lost food production. To demonstrate the complex interrelationships between plants and public health, we present four case studies on plant health issues directly tied to food safety and/or security, and how a One Health approach influences the perception and mitigation of these issues. Plant pathogens affect food availability and consequently food security through reductions in yield and plant mortality as shown through the first case study of banana Xanthomonas wilt in East and Central Africa. Case studies 2, 3 and 4 highlight ways in which the safety of plant-based foods can also be compromised. Case study 2 describes the role of mycotoxin-producing plant-colonizing fungi in human and animal disease and examines lessons learned from outbreaks of aflatoxicosis in Kenya. Plants may also serve as vectors of human pathogens as seen in case study 3, with an example of Escherichia coli (E. coli) contamination of lettuce in North America. Finally, case study 4 focuses on the use of pesticides in Suriname, a complex issue intimately tied to food security though protection of crops from diseases and pests, while also a food safety issue through misuse. These cases from around the world in low to high income countries point to the need for interdisciplinary teams to solve complex plant health problems. Through these case studies, we examine challenges and opportunities moving forward for mitigating negative public health consequences and ensuring health equity. Advances in surveillance technology and functional and streamlined workflow, from data collection, analyses, risk assessment, reporting, and information sharing are needed to improve the response to emergence and spread of plant-related pathogens and pests. Our case studies point to the importance of collaboration in responses to plant health issues that may become public health emergencies and the value of the One Health approach in ensuring food safety and food security for the global population.