▪ Abstract Research on impacts of climate change on plant diseases has been limited, with most work concentrating on the effects of a single atmospheric constituent or meteorological variable on the host, pathogen, or the interaction of the two under controlled conditions. Results indicate that climate change could alter stages and rates of development of the pathogen, modify host resistance, and result in changes in the physiology of host-pathogen interactions. The most likely consequences are shifts in the geographical distribution of host and pathogen and altered crop losses, caused in part by changes in the efficacy of control strategies. Recent developments in experimental and modeling techniques offer considerable promise for developing an improved capability for climate change impact assessment and mitigation. Compared with major technological, environmental, and socioeconomic changes affecting agricultural production during the next century, climate change may be less important; it will, however, add another layer of complexity and uncertainty onto a system that is already exceedingly difficult to manage on a sustainable basis. Intensified research on climate change–related issues could result in improved understanding and management of plant diseases in the face of current and future climate extremes.

SUMMARY: A biological attack on U.S. crops, rangelands, or forests could reduce yield and quality, erode consumer confidence, affect economic health and the environment, and possibly impact human nutrition and international relations. Preparedness for a crop bioterror event requires a strong national security plan that includes steps for microbial forensics and criminal attribution. However, U.S. crop producers, consultants, and agricultural scientists have traditionally focused primarily on strategies for prevention and management of diseases introduced naturally or unintentionally rather than on responding appropriately to an intentional pathogen introduction. We assess currently available information, technologies, and resources that were developed originally to ensure plant health but also could be utilized for postintroduction plant pathogen forensics. Recommendations for prioritization of efforts and resource expenditures needed to enhance our plant pathogen forensics capabilities are presented.

The ability to infect host flowers offers important ecological benefits to plant-parasitic fungi; not surprisingly, therefore, numerous fungal species from a wide range of taxonomic groups have adopted a life style that involves flower infection. Although flower-infecting fungi are very diverse, they can be classified readily into three major groups: opportunistic, unspecialized pathogens causing necrotic symptoms such as blossom blights (group 1), and specialist flower pathogens which infect inflorescences either through the gynoecium (group 2) or systemically through the apical meristem (group 3). This three-tier system is supported by life history attributes such as host range, mode of spore transmission, degree of host sterilization as a result of infection, and whether or not the fungus undergoes an obligate sexual cycle, produces resting spores in affected inflorescences, and is r- or K-selected. Across the three groups, the flower as an infection court poses important challenges for disease management. Ecologically and evolutionarily, terms and concepts borrowed from the study of venereal (sexually transmitted) diseases of animals do not adequately capture the range of strategies employed by fungi that infect flowers.

The science of climate change has matured considerably during the past decade, both relative to the strength of the evidence documenting the ongoing anthropogenic climate change and in terms of the quality of climate models projecting future changes in climate. Concomitantly, modeling studies to project the likely impacts of climate change on agricultural production also have become more sophisticated. Nonetheless, agricultural impact assessments still do not account for all important factors; for example, potential changes in yield losses due to altered dynamics and intensity of pests (insects, plant pathogens, and weeds) under climate change are generally ignored — an important omission, given the significant role of plant pests in constraining the production of food and fiber worldwide. This paper highlights selected challenges that must be overcome before we can hope to quantify the impacts of a changing climate on plant disease intensity and yield loss. They pertain both to retrospective analyses seeking to identify fingerprints related to climate change in long-term plant-disease records, as well as to the use of mathematical models to predict likely impacts on plant pathosystems in the future. The use of climate-change fingerprints has been limited because time series containing disease variables collected in a standardized manner are unavailable for most plant pathogens; in cases where such long-term records do exist, trends are often confounded by changes in biological or management factors over time. As for the use of models for impact assessment, key challenges pertain to uncertainty in input variables, the difficulty in predicting biological responses in the presence of nonlinearities and thresholds, and the high likelihood of genetic adaptation to climate change.