Evidence for heterologous encapsidation of potato spindle tuber viroid in particles of potato leafroll virus.

The aphid Myzus persicae (Sulz.) was shown to transmit potato spindle tuber viroid (PSTVd) to potato clone DTO-33 from source plants doubly infected with potato leafroll virus (PLRV) and PSTVd. Transmission was of the persistent type and did not occur when the insects were allowed to feed on singly infected plants. Only low levels of PSTVd were associated with purified PLRV virions, but its resistance to digestion with micrococcal nuclease indicates that the viroid RNA is encapsidated within the PLRV particles. Epidemiological surveys carried out at three locations in China revealed a strong correlation between PSTVd infection and the presence of PLRV, suggesting that PLRV can facilitate PSTVd spread under field conditions.