VIEW ARTICLE

Resistance

Competition for Infection Sites and Multiplication of the Competing Strain in Plant Viral Interference. J. L. Sherwood, Former graduate research assistant, Department of Plant Pathology, 1630 Linden Drive, University of Wisconsin, Madison 53706, Present address of senior author: Department of Plant Pathology, Oklahoma State University, Stillwater 74078; R. W. Fulton, professor, Department of Plant Pathology, 1630 Linden Drive, University of Wisconsin, Madison 53706. Phytopathology 73:1363-1365. Accepted for publication 14 February 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1363.

Interference between common tobacco mosaic virus (TMV-C), which causes mosaic in leaves of Nicotiana sylvestris, and a strain of the virus from petunia (TMV-P, which causes necrotic lesions in leaves of N. sylvestris) was investigated in leaves of infected plants showing mosaic (mosaic leaves) and in leaves on uninoculated plants (healthy leaves). TMV-C inoculum added to TMV-P inoculum reduced numbers of lesions in healthy leaves in proportion to the amount added. In mosaic leaves, however, in which TMV-P causes lesions in the dark green tissue, lesion numbers were reduced only slightly as the ratio of TMV-C to TMV-P was increased. Ultraviolet-inactivated TMV-C, TMV coat protein, or bovine serum albumin added to TMV-P reduced lesions in both healthy and mosaic leaves as did TMV-C added to TMV-P in mosaic leaves. This suggested that infection sites were being blocked nonspecifically. TMV-C RNA added to TMV-P virions reduced lesion numbers more in healthy than in mosaic leaves, but the RNA did not interfere with TMV-P to the extent that the virions did. Unlike the nonspecific interference by various proteins, yeast RNA did not interfere with lesion production by TMV-P in healthy or mosaic leaves. This suggested that the specificity of interference lies at the virus-replication stage. We conclude that both competition for infection sites and multiplication of the interfering strain are involved in the interference phenomenon.