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

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Abstract
Phenotypic expression of different genes controlling resistance to tobacco mosaic virus (TMV) in tomato was analyzed 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 and 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, 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.