Resistance to Tobacco Mosaic Virus in Tomato: Effects of the Tm-1 Gene on Virus Multiplication

Abstract

The gene Tm-1 in tomato plants is dominant for suppression of mosaic symptoms caused by tobacco mosaic virus isolates designated as tomato strain O. Virus multiplication (measured either by virus RNA content or by virus coat protein content) was inhibited in plants containing Tm-1. Inhibition was greater in hosts homozygous for Tm-1 (90-95%) than in hosts heterozygous for Tm-1 (65-75%). Thus, inhibition of tobacco mosaic virus multiplication is Tm-1 gene dosage-dependent; suppression of visible symptoms is not. Inhibition of TMV RNA accumulation occurred in directly inoculated and systemically-infected leaves of Tm-1-containing hosts and was consistent from experiment to experiment. Tm-1 inhibited accumulation of RNA of different isolates of strain O to different extents: 2 isolates causing yellow mosaic symptoms on susceptible plants were especially strongly inhibited. In Tm-1 hosts there was a delay between inoculation and the first detection of virus multiplication, measured either as increase in virus RNA content or recoverable infectivity. The delay was about 8 days in heterozygous Tm-1 hosts and about 16 days in homozygous Tm-1 hosts. The implications of the results for the mode of action of the Tm-1 gene resistance are discussed.