Characterization of Potyvirus Isolates from West African Yams (Dioscorea spp.)

Abstract

AbstractIn comparative studies on potyviruses from West African yams (Dioscorea spp.) the following isolates were used: Dioscorea greenbanding mosaic virus (DGMV) and a Nigerian yam virus (YV‐N), both isolated from Dioscorea rotundata, and a beet mosaic virus isolate from D. alata (BtMV‐Y) formerly designated Dioscorea alata ring mottle virus. Naturally infected D. alata containing very few particles of BtMV‐Y, contained primarily particles of a second potyvirus (Dioscorea alata virus, DaV) which could not be transmitted but which was included in these studies wherever possible.The normal lengths of DGMV, YV‐N, DaV, and BtMV‐Y were 754, 772, 805, and 812 nm, respectively. All viruses induced cytplasmic inclusions of the pinwheel type and laminated aggregates. In addition, the nucleoli of BtMV‐Y infected cells contained characteristic electron dense inclusions. The buoyant density of purified DGMV and BtMV‐Y in CsCl was 1.336 g/cm3 and 1.321 g/cm3, respectively. The sedimention velocities (Srel) of DGMV, YV‐N, and BtMV‐Y were 156, 158, and 162 Srespectively. In SDS‐polyacrylamide gel electrophoresis the coat protein of purified DGMV and YV‐N all migrated as a single band with an apparent molecular weight of 36 kd. Coat protein of purified DaV showed up to 5 bands with molecular weights of 36 to, 32 kd. Polypeptides of purified BtMV‐Y had an estimated molecular weight of 35 kd but those from infected plant extracts had a molecular weight of 36 kd. DGMV, YV‐N, and BtMV‐Y particles contained a single nucleic acid with an apparent molecular weightof 3.2, 3.2, and 3.1 Md, respectively. Using λ‐DNA digested with Hind III as a marker, the molecular weight of DGMV and BtMV‐Y nucleic acid was calculated to be 3.6 Md ± 10%. The nucleic acid was determined to be single‐stranded RNA by enzymatic digestion and by staining with acridine orange.In serological studies using immunoelectron microscopy (IEM), electro‐blot immunoassay (EBIA), and enzyme‐linked immunosorbent assay (ELISA), DGMV and YV‐N were closely related. Strong serological reactions were also obtained in IEM and EBIA when DGMV and YV‐N were tested with antiserum to yam mosaic virus (YMV). Antisera against DGMV, YV‐N, and YMV also reacted strongly with DaV antigen. Serological reactions between these viruses and BtMV‐Y were usually not found or were weak. A very close serological relationship could be detected between BtMV‐Y and beet mosaic virus isolated from beet (BtMV); both isolates were also very similar in host range, symptomatology, and cytopathology.