Emerging Infectious Plant Diseases

This chapter provides insights into the types of biotic threats to plants, the nature of the U.S. plant health infrastructure, the resources available to address and mitigate losses due to emerging plant diseases, and whether they arise as a result of the arrival of exotic pathogens, the mutation of endemic pathogens, or the intentional dissemination of pathogens by perpetrators wishing to cause harm. Pathogens of plants, like those of animal and human hosts, belong to a number of different taxa including fungi, oomycetes, bacteria, viruses, nematodes, protozoa, and even parasitic plants. Technologies relying on more complex chemistry and instrumentation, such as PCR, microarrays, or sequence-based assays, may provide definitive identification of a pathogen but lack portability and thus are more often deployed in clinical laboratories. Natural means of spread include weather, biological features such as aerodynamic spore morphology, the involvement of biological vectors, moving water, and even being borne on seeds or pollen, which are adapted for their own dissemination. These mechanisms, and their implications for disease epidemiology, are discussed in the chapter. Emerging, infectious plant diseases have long been of concern not only to growers and plant pathologists but also to legislators and policy makers. Although plant diseases generally do not cause immediate, acute, or lethal consequences for humans, they can and do result in significant economic harm, as trade is affected, and rural communities and downstream industries experience the impacts of crop quarantines, trade embargoes, and loss of income.