cytological comparison of inclusions as a basis for distinguishing two filamentous legume Viruses

Agronomy and Plant Pathology Departments, Plant Virus Laboratory, University of Florida, Gainesville, Florida 32601, U.S.A., and Botany Department, University of Guelph, Guelph, Ontario, Canada Light and electron microscopy were used to compare two flexuous-rod viruses: cowpea virus (CV) and bean yellow mosaic virus (BYMV). Inclusions induced by CV were consistently different from those induced by BYMV. In the light microscope, BYMV-induced cylindrical inclusions appeared as a group of plates, whereas CV-induced cylindrical inclusions appeared as a group of tubes. Electron microscopy showed that CV induced fibrous nuclear inclusions, while BYMV induced non-fibrous nucleolar inclusions in Crotalaria spectabilis . Thin section studies showed that CV-induced cylindrical inclusions contained circles and tubes, but no laminated aggregates, while BYMV-induced cylindrical inclusions contained laminated aggregates, but no circles or tubes. The shapes of extracted inclusions induced by CV were consistently different from those induced by BYMV. These viruses are cytologically different and are believed to be distinct. Received 26 October 1971; accepted 16 December 1971.