STANDARDIZATION IN INOCULATION PROCEDURE AND EFFECT OF A RESISTANCE GENE ON INFECTION OF TOMATO PROTOPLASTS WITH TOBACCO MOSAIC-VIRUS RNA

Inoculation at 0°C improved the efficiency of infecting tomato protoplasts with RNA of tobacco mosaic virus (TMV). Up to 41% infection was obtained when inoculation was at 0°C with μg/ml RNA in the presence of 1 μg/ml poly-D-lysine in 0.01 M-potassium citrate buffered 0.7 M-mannitol (pH 5.2). The homozygous gene for resistance Tm-I was expressed in tomato protoplasts inoculated with RNA of TMV-L, a common tomato strain of TMV; no virus progeny were detected by fluorescent antibody staining or infectivity assay. Virus multiplied rapidly in protoplasts from susceptible homozygotes. Protoplasts homozygous for Tm-I were infected by the RNA of TMV-CH2, a tomato strain which can overcome this resistance in plants. These results resemble those previously reported for inocula using intact virus, and suggest that Tm-I blocks virus growth after the uncoating stage.