ABSTRACT
It is commonly observed that wherever plants are grown for food or fiber they are fed upon and damaged by insects and mites, and that they compete with other plants (i.e., weeds) for water, nutrients, and sometimes sunlight. In addition, however, plants must fend off and survive numerous diseases. Some diseases are caused by adverse environmental conditions, such as low temperatures, droughts, nutrient deficiencies or toxicities, air pollutants, and the like. Most importantly, however, plants must avoid or survive diseases caused by organisms that live in or on the plant, obtain nutrients from the plant, and through their presence and through substances they produce, affect the normal functions of the plants to the point where plants become diseased, produce less, and frequently die from the disease.
