Electron microscopy of ultrathin sections of tissues from Ribes plants affected with blackcurrant reversion (BRD) and gooseberry veinbanding (GVD) diseases was studied. In 3 of 12 blackcurrant plants affected with BRD, leaves and flowers showing symptoms typical of the severe form of the disease, contained rhabdovirus-like particles c. 65-80 x 215-485 nm. They were seen most often in the nucleus of cells as single particles but were also found in clusters or rafts. In leaves, the virus-like particles were present in <1% cells associated with the xylem parenchyma, where they occurred as membrane-bound clusters within the nucleus. In leaf tissue of 1 of 3 gooseberry and 1 of 2 blackcurrant plants affected with GVD, similar rhabdovirus-like particles were found in the cytoplasm of phloem cells. In addition, filamentous particles were found in non-crystalline masses, with a mean centre-centre spacing of c. 10 nm. These particles, together with other ultrastructural changes, were typical of those reported for aphid-transmitted closteroviruses.
Clostero-like particles were found by electron microscopy of sap extracted from leaves of a single symptomless plant of Chenopodium murale inoculated previously with sap from GVD-affected gooseberry, detected. When sap from GVD-affected gooseberry was inoculated to Nicotiana occidentalis 37B, a single necrotic lesion developed in one plant. Electron microscopy of sap extracted from the region of this lesion detected several badnavirus-like particles c. 130 x 30 nm.