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The reactivity of monoclonal antibodies (McAbs) to the coat protein of tobacco mosaic virus (TMVP) with the isolated coat protein, disks, virions and a number of antigenic variants of TMV was tested in eight different ELISA procedures. Although certain McAbs, when used as detecting antibody in the liquid phase, did not react with some of these antigens, they were able to bind to them when used as the capturing antibody on the solid phase. This finding was attributed to the ability of the trapping McAb to induce a complementary conformation in the antigen presented in the liquid phase. In many cases, the reactivity of the McAbs was found to depend on the format of the ELISA. This finding together with the presence of oligomers in viral coat protein preparations made it impossible to map TMVP epitopes on the surface of the viral subunit by means of competitive ELISA.

Summary Rabbit polyclonal antisera raised against six different isolates of maize streak virus (MSV) were used to determine the serological relationships among a range of MSV isolates from different plant species originating from various African countries and from Vanuatu. Their reactions indicated a great serological diversity among these isolates. Fifteen monoclonal antibodies (MAbs) raised against a Nigerian maize isolate, MSV-M(N)M, were characterized according to their reactivity with the various MSV isolates in indirect ELISA. All the MAbs reacted with the virus both in an antigen-coated plate and in a double antibody sandwich ELISA. None of the MAbs reacted with all isolates, and some isolates most distantly related to MSV-M(N)M according to results obtained with polyclonal antisera were not recognized by any of the MAbs. Some isolates which were shown to be closely related using the polyclonal antisera could be distinguished by several of the MAbs. The results obtained both with the polyclonal antisera and the MAbs suggested that several of the isolates were a mixture of a number of different serotypes.

Five monoclonal antibodies (McAbs) were raised to the tobamovirus, odontoglossum ringspot virus (ORSV). All five McAbs reacted with the virus in double antibody sandwich (DAS) ELISA but not in an ELISA using virus-coated plates. All the McAbs recognized a panel of ORSV strains and isolates, although one of the antibodies reacted better with some isolates and another reacted less with certain isolates than with type ORSV. It was possible to use the same McAbs both as coating and as biotinylated antibody in DAS-ELISA. None of the five McAbs was able to bind to orchid strains of tobacco mosaic virus (TMV). In order to detect strains of both viruses, ORSV and TMV, in infected orchids it was necessary to include also McAbs raised against TMV in the immunoassays. The use of a mixed polyclonal-monoclonal antibody DAS-ELISA system is advocated for detecting both tobamoviruses in orchids.

Ten monoclonal antibodies (McAbs) were raised to the tobamovirus, tomato mosaic virus (ToMV). Seven of the McAbs reacted with ToMV only when tested in an ELISA format, involving antibody-coated plates, which preserved the quaternary conformation of the viral protein. Two McAbs which reacted with ToMV only in an ELISA using virus-coated plates recognized an antigenic determinant present only on the disassembled form of the viral coat protein. One McAb reacted with both the assembled and dissociated forms of ToMV protein. All McAbs reacted in an identical manner with the 15 ToMV strains and isolates tested, confirming the previously established serological homogeneity of the ToMV species. Only two of the McAbs cross-reacted with two other tobamoviruses: tobacco mosaic virus (TMV) and ribgrass mosaic virus. Seven variations of ELISA were compared for their suitability to detect ToMV and TMV in tomato plants. Double antibody sandwich ELISA could be performed with a single McAb to ToMV as enough accessible epitopes are present on the virus to bind simultaneously to the coating and biotin-labelled antibody.