The entire genomic RNA of a Spanish isolate of pepper mild mottle virus (PMMV-S), a resistance-breaking virus in pepper, was cloned and sequenced and shown to be similar to other tobamoviruses in its genomic organization. It consisted of 6357 nucleotides (nt) and contained four open reading frames (ORFs) which encode a 126K protein and a readthrough 183K protein (nt 70 to 4908), a 28K protein (nt 4909 to 5682) and a 17.5K coat protein (nt 5685 to 6158). This is the first tobamovirus in which none of the ORFs overlap. Both its nucleic acid and predicted protein sequences were compared with the previously determined sequences of other tobamoviruses. The variations and similarities found and their relationship with the pathogenicity of this virus are discussed.

During a four‐year (1982–1985) survey of plant viruses infecting pepper cultivars grown under plastic in the Southeastern region of Spain, a tobamovirus was found to be the major disease agent of this crop. The virus produces slight or no symptoms on the leaves, but causes chlorotic mottling, malformation and reduction in size with occasional necrosis on the fruits and was able to infect all commercial pepper cultivars tested, including those resistant to other tobamoviruses, causing a catastrophic disease. The biological and serological characterization of the virus showed that it is very similar to pepper mild mottle virus (PMMV) (Wetteret al. 1984) and therefore we have termed it as Spanish strain of PMMV (PMMV‐S). The need of grouping all the so‐called “pepper strains” of tobacco mosaic virus (TMV) as a new distinct member of the tobamovirus group with the name of PMMV is emphasized.

SUMMARYThe nucleotide sequences of the 5' and 3' non-coding regions of pepper mild mottle virus strain S (PMMV-S) RNA were determined; they are more like corresponding sequences of tomato mosaic virus (ToMV) RNA than those of any other tobamovirus reported so far. The 5' leader contains a 68 nucleotide guanosine-free sequence which differs in several nucleotides from the corresponding sequences in genomic RNA of tobacco mosaic virus (TMV) and ToMV. The messenger activity of PMMV-S RNA in vitro and the polypeptide translation products made were similar to those of TMV RNA. It therefore seems unlikely that qualitative or quantitative differences in translation in vivo account for the milder symptoms induced by PMMV-S, and its lesser replication, than TMV. The 3' non-coding region of PMMV-S RNA is 199 nucleotides long and can be folded into the same secondary structure as the RNA of other tobamoviruses.

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