Mechanical transmission of Potato leafroll virus.

Like typical luteoviruses, Potato leafroll virus (PLRV) cannot be transmitted mechanically by rubbing plants with solutions containing virus particles. However, PLRV was found to be mechanically transmissible from extracts of plants that had been inoculated by viruliferous aphids and then post-inoculated with Pea enation mosaic virus-2 (PEMV-2). Unlike the asymptomatic infections induced by either virus alone, double infections in Nicotiana benthamiana induced necrotic symptoms with some line patterning and vein yellowing. Infective PLRV was recovered from a purified virus preparation by inoculating plants mechanically with purified virus particles mixed with PEMV-2. Similarly, Beet mild yellowing virus was readily transmitted mechanically from mixtures containing PEMV-2. PLRV was also transmissible from mixtures made with extracts of plants infected with Groundnut rosette virus, although less efficiently than from mixtures containing PEMV-2. This novel means of transmitting PLRV, and perhaps other poleroviruses, should prove very useful in a number of fields of luteovirus research.