Five isolates of the beetle-transmitted cowpea mosaic virus were studied. The symptoms produced by each on a number of hosts were described. The occurrence of amorphous inclusion bodies in the epidermal cells of infected cowpea and pea plants was reported. A purification procedure was described. Three peaks were invariably associated with the purified virus in the analytical ultracentrifuge, the sedimentation coefficients of these components being 58, 100 and 119 S after separation. The components could be purified by density-gradient centrifugation. The top component was not infective; the middle component was far more infective than the bottom component. Purified preparations showed, by electron-microscopy, polyhedral particles of about 25 mμdiameter. Negative staining of the preparations with phosphotungstate revealed empty particles, and of particles apparently containing nucleic acid. An icosahedral model with 60 subunits and 5: 3: 2 axial symmetry was most compatible with the structure of the particles seen on the electron-micrographs. On the basis of homologous and heterologous serological reactions the five isolates could be divided into two groups. They proved also to be serologically related to bean pod mottle virus and to an isolate of red clover mottle virus.
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