A quantitative study of the interaction of viruses in plants

Abstract

In protective inoculation experiments conducted at Rothamsted, two pairs of related viruses were used. Tobacco and Nicotiana glutinosa plants inoculated with tobacco mosaic virus or potato virus X^G (which cause systemic mottling symptoms in these plants) acquired immunity from tomato aucuba mosaic or potato virus X^s (which cause necrotic local lesions in the test plants). When the tips of tobacco leaves were inoculated with either tobacco mosaic or X^G virus and reinoculated with tomato aucuba mosaic or potato virus X^s after an increasing interval, the results showed that the X^G inoculated areas were quite immune from X^s after 12 days and the tobacco mosaic virus areas immune from aucuba mosaic virus after 4 days. The bases of such leaves showed incomplete inhibition even after 20 and 24 days. When the bases of the leaves were inoculated the results were essentially the same but the leaf tips acquired resistance much more slowly and incompletely. When X^s or aucuba mosaic viruses were mixed in vitro with healthy plant sap or sap containing an unrelated virus, the infectivity of these viruses was reduced, but this inhibitory effect was much greater when they were mixed with their related strains. It is concluded that in the plant tissue there is an intense competition between related viruses, and evidence was obtained that the degree of resistance to one is directly proportional to the amount of the other present.