INTERACTION OF VIRUSES IN THE HOST
No attempt will be made to arrive at statistics on the relative frequency of interaction between unrelated viruses compared to that between related ones. To do so seems fruitless, for I suspect that interaction is the norm, not the exception, and can be expected to occur in some way to some extent between any pair of viruses, whether related or not. Infection by any virus affects the plant - its physiology, metabolic activity, or even structure - in some way. If nothing more, a new type of RNA synthesis is imposed and plant components and systems are utilized for synthesis of virus and associated proteins in competition with normal activities. General experience tells us that almost any change in the host, regardless of the cause, is very likely to affect the ease with which infection by a virus can be initiated, the extent of subsequent virus replication, and/or the host response. Another way of saying this is that a virus-infected plant is not identical with a healthy one and thus it would be surprising if the two reacted to a second virus in exactly the same way. In my look at the types of interactions that occur, major attention will be given to quantitative aspects and timing of these interactions, i.e., whether they are marked, moderate, or slight and when they occur with respect to the replication cycle of each virus.