Figure 1. Formation of necrotic local lesions on a leaf of the indicator plant Gomphrena globosa after rubbing with sap from a virus-infected plant.

Figure 2. Various morphological types of plant viruses. Helically constructed filamentous (flexible) particles with positive-sense ssRNA genomes: beet yellows Closterovirus (a), potato X Potexvirus (b) and potato Y Potyvirus (c). Helically constructed rod-like particles with positive-sense ssRNA genomes: tobacco mosaic Tobamovirus (d), barley stripe mosaic Hordeivirus (e) and tobacco rattle Tobravirus (f). Icosahedral 25–30-nm thick particles with positive-sense ssRNA genomes with different surface fine structures: maize chlorotic mottle Machlomovirus (g), barley yellow dwarf Luteovirus (h), cucumber mosaic Cucumovirus (i) and arabis mosaic Nepovirus (j). Irregularly shaped isometric to bacilliform particles with positive-sense ssRNA genomes: apple mosaic Ilarvirus (k) and alfalfa mosaic Alfamovirus (l). Geminate or isometric 18-nm thick particles with ssDNA genomes: tomato yellow leaf curl Begomovirus (m) and faba bean necrotic yellows Nanovirus (n). Isometric or bacilliform particles with DNA and RNA reverse transcribing dsDNA genomes: cauliflower mosaic Caulimovirus (o) and cacao swollen shoot Badnavirus(p); Bullet-shaped or spherical particles with negative-sense ssRNA genomes: Laelia red leaf spot-type Rhabdovirus (q) and tomato spotted wilt Tospovirus (r). (a)–(f) bar, 500 nm; (g)–(r) bar, 100 nm.

Figure 3. Electron-microscopically visible alterations due to virus infections.(a) Plate-like cytoplasmic aggregate formed by the particles of a rod-shaped virus (cross-section); the highly regular in vivo arrangement with particle ends in register has been disturbed during fixation. Bar, 500 nm. (b) Ultrathin cross-sections of pinwheels (PW), scrolls (SC) and laminated aggregates (LA) formed by a nonstructural protein of a potyvirus. Bar, 500 nm. (c) Flask-shaped vesicles associated with the peripheral membrane of a chloroplast typical for tymovirus infections; the fibrillar content of the vesicles suggests the presence of dsRNA. Bar, 500 nm.

Figure 4. Principle of (a) the agar gel double diffusion test, and (b) immunoelectrophoresis.

Figure 5. Formation of single and multiple precipitin lines in the agar gel double diffusion test by highly (left) and partially (right) purified virus preparations, which were tested with an antiserum (lower well) containing antibodies to the virus as well as to normal plant constituents; the precipitin lines bending around the antigen wells are formed by the virus, and the straight line by normal plant constituents.

Figure 6. Patterns of precipitin lines formed in the agar gel double diffusion test when two viruses in neighbouring wells are tested against one antiserum: the complete fusion of the precipitin lines in the upper part of the figure indicates that the two viruses are serologically identical; the spur formation in the lower left part indicates that the two viruses are serologically related, but not identical; the crossing of the lines in the lower right part indicates that the two viruses are serologically unrelated and that the antiserum had contained antibodies to both of them.

Figure 7. Principle of double antibody sandwich enzyme (Enz)-linked immunosorbent assay (ELISA).

Figure 8. Principle of tissue print immunoblotting.

Figure 9. Principle of various electron microscopical tests: (a) simple adsorption of virus particles to a support film on a grid; (b) specific binding of an increased number of particles to an antibody-coated grid in immunosorbent electronmicroscopy (ISEM); and (c) decoration of particles by antibodies.

Figure 10. Immunoelectron microscopical analyses of virus-containing fluids. (a) Many virus particles are trapped within 15 min on a grid which had been coated with the homologous antiserum. (b) Only one particle is adsorbed nonspecifically, from the same extract as in (a), on a grid coated with serum from a nonimmunized rabbit. (c) Detection of a mixed infection with two morphologically indistinguishable viruses; only those virus particles for which the antiserum is specific are decorated. (d) Binding of monoclonal antibodies to virus particles visualized by immunogold labelling (10-nm gold particles in the upper and lower parts and 5-nm gold particles in the middle part of the figure, respectively). In the upper part of (d) the antibodies are bound along the entire surface of the particle; in the middle and lower parts, on one or both extremities of the particles, respectively. (a)–(c) bar, 500 nm, (d) bar, 100 nm.

Figure 11. Principle of the immunocapture reverse transcription polymerase chain reaction (PCR).