Expression of Genetically Controlled Resistance to Tobacco Mosaic Virus Infection in Isolated Tomato Leaf Mesophyll Protoplasts

SUMMARY Phenotypic expression of different genes controlling resistance to tobacco mosaic virus (TMV) in tomato was analysed in the protoplast system using otherwise isogenic breeding lines. Genes Tm-2 and Tm-22 were not expressed and did not prevent TMV-L, a common tomato strain of TMV, infecting and multiplying. By contrast, homozygous gene Tm-1 was able to express its effect in protoplasts as well as in leaf discs; no virus progeny were detected by fluorescent antibody staining or by infectivity assay up to 3 days after inoculation with TMV-L. Protoplasts and leaf discs homozygous for Tm-1, however, became infected with TMV-CH2, a tomato strain able to overcome the effects of Tm-1 in intact plants. Protoplasts from Lycopersicon peruvianum P. I. 128650, known to have a high level of resistance to TMV, were as readily infected with TMV-L, and synthesized progeny virus as rapidly as protoplasts from susceptible tomato. This genotype seems to have no resistance expressible in isolated protoplasts.