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White clover cryptic viruses (WCCV) 1, 2, and 3 were purified from apparently healthy plants with yields of about 200 μg of virus/kg of tissue. After isopycnic centrifugation in CsCl, WCCV 1 and 2 formed homogeneous bands at densities of 1.392 and 1.375 g/ml, respectively, whereas WCCV 3 was not recovered. Particles of WCCV 1 and 3 were 34 nm in diameter, without obvious morphological subunits, whereas WCCV 2 particles were 38 nm in diameter, with prominent morphological subunits. Antisera with titers up to 1:2048 were obtained against WCCV 1 and 2. Each of the three viruses contained two segments of linear dsRNA ( M r from 1.03 to 1.49 X 10 −6 . Virus-like particles, probably those of WCCV 1 and 2 were detected in low numbers in the cytoplasm of about 1/10 of the parenchyma cells of carrier plants examined by thin sectioning. The particles of WCCV 1 and 2 were not transmitted by grafting or mechanical inoculation, but were seed transmitted. Evidence is given that WCCV 1 and 2 multiply in their carrier plants, and are not viruses of associated parasitic or commensal organisms.

A serological analysis was made on maize rough dwarf virus fractions by immune electron microscopy, gel diffusion and slide precipitin tests to investigate the reactions of both protein and RNA. Antisera were made against different virus fractions, and existing sera against rice black streaked dwarf and maize rough dwarf viruses were also tested. Some of the sera contained antibodies against viral dsRNA. The serological behavior of poly[I]:poly[C] was similar to but not identical with that of viral RNA. One antigenic group in smooth cores was identified, and an additional group was found in spiked cores, associated with B spikes. Attempts to obtain antibodies against the outer capsid were not successful. A soluble antigen was identified as viral RNA. Disrupted protein preparations containing sodium dodecyl sulfate reacted with normal sera as well as virus antisera.

Two immune electron microscopic methods are described that allow rapid demonstration of (a) specific antibody coating of virus particles or (b) specific clumping and a tenfold increase in the number of particles visible on the grid. The operations take only 20 min and produce high-resolution images not only with purified preparations but also with crude preparations or those containing salts, buffers or sucrose.