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Until recently, sugarcane mosaic virus (SCMV) was believed to be a single potyvirus consisting of a large number of strains, differing from each other in certain biological and antigenic properties. The use of affinity-purified polyclonal antibodies directed towards the surface-located, virus-specific amino termini of the coat proteins showed that 17 strains from Australia and the United States represented four distinct potyviruses, namely johnsongrass mosaic virus (JGMV), maize dwarf mosaic virus (MDMV), sorghum mosaic virus (SrMV) and SCMV. Comparisons of strains from each of these four viruses on the basis of reactions on differential sorghum and oat cultivars, cell-free translation of RNAs, morphology and serology of cytoplasmic cylindrical inclusions, amino acid sequence and peptide profiling of coat proteins, 3′ non-coding nucleotide sequences, and molecular hybridization with probes corresponding to the 3′ non-coding regions, resulted in exactly the same taxonomie assignments as obtained using amino-terminal serology. These results further confirm that the former sugarcane mosaic virus actually consists of four distinct viruses and show that MDMV, SrMV, and SCMV are more closely related to each other than they are to JGMV. Because these four viruses are closely related but distinct, formation of a sugarcane mosaic subgroup in the genus Potyvirus would be appropriate.

A cytological comparison has been made of representative isolates of johnsongrass mosaic (JGMV), maize dwarf mosaic (MDMV), sorghum mosaic (SrMV) and sugarcane mosaic (SCMV) viruses. These four viruses now encompass the complex of virus strains which were formerly considered as strains of sugarcane mosaic and/or maize dwarf mosaic viruses. The structure of the cytoplasmic cylindrical inclusions induced by these viruses, together with other cytological alterations, allow the four viruses to be distinguished. Pinwheels, scrolls and laminated aggregates were produced only by SCMV whereas JGMV, MDMV, and SrMV produced only pinwheels and scrolls. SrMV produced amorphous cytoplasmic inclusions which are not produced by JGMV and MDMV. The latter two were rather similar in cytological effects except that the SCMV-JG (U.S.A.) isolate of MDMV produced aggregates of needle-like structures in the cytoplasm which were not found with JGMV and the other MDMV isolates. The specific cytological effects induced by these viruses thus corroborate the recent classification of these viruses based mainly on the properties of the coat-protein gene, the 3′ non-coding nucleotide sequences, and host reactions.

Cross-protection was studied between strains of viruses comprising the sugarcane mosaic virus (SCMV) subgroup, namely Johnsongrass mosaic, maize dwarf mosaic, sorghum mosaic, and SCMV, in 53 different combinations using differential hosts and Western blot immunoassays, Cross-protection occurred only between SCMV-MDB and SCMV-BC when the former was inoculated first and the latter used as the challenge strain, but neither vice versa nor in any other combinations including the 19 that involved recognized strains of the one virus, SCMV. The unidirectional protection between SCMV-MDB and SCMV-BC and the negative cross-protection results between other strains of SCMV appear to correlate with different sequence motifs present in the hypervariable region of the coat protein N-terminus of the SCMV strains

A number of potyvirus isolates have been identified as strains of soybean mosaic virus (SMV) on the basis of host range, symptomatology, vector specifiicity, and antigenic properties. Comparison of recently established coat protein gene sequences of two of the strains, SMV-N and SMV-VA, suggested that they represent two distinct potyviruses. The taxonomic status of other strains relative to these two strains is uncertain at present. To address this question we have compared high-performance liquid chromatographic peptide profiles of coat protein tryptic digests from 14 such strains, including SMV-N and SMV-VA (...)

The taxonomic status of sugarcane mosaic virus (SCMV) strains reported from various parts of the world has been uncertain. Previous analyses of 17 SCMV strains with virus-specific polyclonal antibodies demonstrated that they represent four distinct potyviruses, namely Johnsongrass mosaic virus (JGMV), maize dwarf mosaic virus (MDMV), sorghum mosaic virus (SrMV), and SCMV. To confirm this classification, we have now compared six strains of SCMV, three strains of JGMV, and two strains each of MDMV and SrMV using high-performance liquid chromatographic (HPLC) peptide profiling of tryptic digests of their coat proteins (...)

Summary Attempts to identify and classify distinct potyviruses and their strains have frequently been hampered by the presence of variable proportions of cross-reacting antibodies in antisera. Investigations of reactivities in electroblot immunoassays of 11 polyclonal antisera raised by injection of intact particles of potyviruses produced in different laboratories with 12 distinct potyviruses showed that such cross-reacting antibodies were directed towards the homologous core protein region of potyvirus coat proteins. A simple method was developed to obtain virus-specific antibodies using affinity chromatography. It involved removal of the surface-located, virus-specific N-terminal peptide region from particles of one potyvirus using lysyl endopeptidase, coupling of the truncated coat protein to cyanogen bromide-activated Sepharose gel, and passing antisera to different potyviruses through the column. Antibodies that did not bind to the column were found to be highly specific.

There are at least ten viruses identified in the literature that resemble definitive potyviruses in having flexuous filamentous particles and inducing the formation of “pinwheel” cytoplasmic inclusions in infected cells but that are transmitted by eriophyid mites, whiteflies or soil fungi and not by aphids, the vectors of the definitive potyviruses. The taxonomic status of these viruses is uncertain at present. Using a broadly cross-reactive antiserum raised against the dissociated coat protein core (residues 68–285) of a definitive potyvirus (Johnsongrass mosaic virus), we have shown that wheat streak mosaic virus which is transmitted by mite and sweet potato mild mottle virus which is transmitted by whitefly have coat proteins that share epitopes with definitive potyviruses. This finding further supports their classification as definitive members of the potyvirus group. The cross-reactive antiserum used here had been shown previously to react with coat proteins of fifteen different definitive potyviruses. The antiserum did not react with coat proteins of potexviruses and tobamoviruses.

(...) In this paper we have compared 17 SCMV/MDMV strains from Australia and the United States on the basis of their reactivities, in electro-blot immunoassay, with cross-absorbed polyclonal antibodies directed towards surface-located, virus-specific N-termini of coat proteins. (...)