Читать книгу Plant Pathology and Plant Pathogens - John A. Lucas - Страница 17

Any agent capable of adversely affecting green plants may be regarded as lying within the scope of plant pathology. The principal agents involved in plant disease are shown in Figure 1.5. Partial or total crop failure may be due to one or more agents. Where more than one agent is responsible, each may act independently, or they may interact. In the latter instance, there may be synergism, that is, two or more agents acting in combination to cause symptoms that are more severe than those produced by either agent alone. Synergism has been demonstrated to occur with several combinations of viruses. For example, tobacco mosaic virus and potato virus X each cause relatively mild mottling symptoms in tomato. But if by chance they both occur together in the same host, then severe necrosis develops and this may even result in the death of the plant.

A useful distinction can be drawn between animate (biotic) and inanimate (abiotic) causes of disease (Figure 1.5). Many of the animate agents, including the microbial pathogens, the parasitic angiosperms, and some of the animal pests, are infectious. Due to their capacity for growth, reproduction, and dispersal, these agents spread from one host plant to another. Under particularly favorable conditions, they may be dispersed rapidly over wide areas and even entire continents.