ABSTRACT
Plant diseases have been observed and recorded by humans for more than 2000 years (Agrios, 1997). Many plant diseases were initially described based on the observation of visible signs (vegetative and reproductive structures of the pathogen) and symptoms (reactions of the plant to infection) on fruits, leaves, roots, and stems. Since then, scientists in the discipline of plant pathology have continued to investigate the causal role that microorganisms play in plant disease and how their biology, ecology, and genetics influence pathogenesis (disease-causing ability of an organism). The majority of scientific studies conducted by plant pathologists have focused primarily on plant species of economic importance to agriculture and fostered the development of experimental methods to examine plant pathogens and their associated diseases. In general, most agricultural crops are subject to many diseases caused by a wide array of plant pathogens. Some of these pathogens have a narrow host range and can only infect a single species or variety of plant, whereas other pathogens have the ability to infect a wider range of hosts often in genetically different families of plants. The intensity and severity of disease can also vary depending on environmental conditions and genetic composition of the pathogen and plant.
