VIEW ARTICLE

Resistance

Studies of the Variable Reaction at High Temperature of F₁ Hybrid Tomato Plants Resistant to Tobacco Mosaic Virus. M. Pilowsky, Division of Plant Genetics and Breeding, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel; R. Frankel(2), and S. Cohen(3). (2)Division of Plant Genetics and Breeding, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel; (3)Virus Laboratory, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. Phytopathology 71:319-323. Accepted for publication 23 July 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-319.

When tomato plants heterozygous for the Tm-2^a gene for resistance to tobacco mosaic virus (TMV) were inoculated and grown at high temperature (30–31 C), they reacted either locally or systemically. No evidence was obtained that the occurrence of two types of symptoms was the result of genetic differences in the parental material; in contrast, the data indicated that the absence of systemic symptoms in a certain percentage of the F₁ plants was due to the amount of virus introduced to them by rubbing inoculation being less than the minimum required for the induction of systemic symptoms. The mechanism of localization of TMV infection in homozygous and heterozygous resistant plants could be overcome if larger numbers of virus particles were introduced into the plants by repeated inoculations prior to their transfer to high temperature. It is suggested that the reaction of plants carrying the Tm-2^a gene (local or systemic) depends on a certain quantitative balance between the host’s resistance mechanism and the virus titer at the primary site of infection.