Interference Experiments relating to whether Tobacco Mosaic Virus and Cucumber Viruses 3 and 4 are Strains of the same Virus

Abstract

THE problem of whether cucumber viruses 3 and 4 (CVS, CV4) and tobacco mosaic virus (TMV) are different viruses or strains of the same virus has been examined in detail by Knight¹. On the basis of several criteria such as host-range, chemical composition, electron microscope morphology, etc., he concluded that they were different viruses. However, two criteria, serology and the ability to exhibit cross-protection, still support the idea that they are strains of the same virus. In regard to cross-protection, it was first found by Fulton² that prior infection of cucumber by CV3 and CV4 did not protect against subsequent TMV infection, but later Rochow⁵ was able to demonstrate a high degree of protection. Apparently, the difference between Fulton's and Rochow's experiments is shown in the length of time the plant is allowed to sustain a CV3 and CV4 infection before it is challenged by a second inoculation with TMV.