Dependence of groundnut rosette virus on its satellite RNA as well as on groundnut rosette assistor luteovirus for transmission by Aphis craccivora

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Abstract
Transmission of groundnut rosette virus (GRV) by Aphis craccivora is known to depend on the additional presence in the source plants of a luteovirus, groundnut rosette assistor virus (GRAV). Naturally occurring isolates of GRV contain a satellite RNA which is the main cause of rosette symptoms in groundnut, different variants of the satellite being responsible for the green and chlorotic forms of rosette. In extensive glasshouse tests, GRAV-dependent transmission of GRV by A. craccivora occurred only from groundnut plants infected with satellite-containing isolates of GRV. This was true whether the GRV isolates were from groundnut plants from Nigeria or Malawi with either the green or chlorotic forms of rosette and whether they contained homologous or heterologous satellites. Aphid transmission of GRV therefore depends not only on the presence of GRAV but also on that of the GRV satellite RNA. This probably explains why satellite-free isolates of GRV have not been found in nature. This is the first report of satellite RNA mediating aphid transmission of a plant virus.