RT-PCR ANALYSIS OF PSTVD APHID TRANSMISSION IN ASSOCIATION WITH PLRV

Potato spindle tuber viroid (PSTVd), once widespread, has not been det ected in commercial potato samples in Canada since 1980. A recent repo rt from the international Potato Center, Peru, shows that PSTVd can be transmitted to 100% of potato plants if source plants are doubly-infe cted with potato leafroll virus (PLRV) and PSTVd. This study was carri ed out to determine if this is the case with the North American isolat e of PLRV and PSTVd. The reverse-transcription polymerase chain reacti on (RT-PCR) was used for the determination of the acquisition and tran smission of both pathogens by aphids (Myzus persicae). The specificity of the observed RT- PCR products to PSTVd and PLRV was confirmed by S outhern blot hybridization with viroid- and virus-specific probes. Aph ids acquired both pathogens from a doubly-infected potato plant; 83-88 % of the aphids acquired PLRV and 30-39% acquired both PLRV + PSTVd. A cquisition of only PSTVd by aphids from a source plant infected only w ith PSTVd was 5% or 3 of the 60 aphids. Five weeks after transfer of t he viruliferous aphids to Physalis floridana, a host plant susceptible to both pathogens, PSTVd was not detected in any of the plants. Durin g the same period, PLRV was transmitted to 1008 of the plants. Eight w eeks later PSTVd was detected in 3 of the 44 PLRV-infected plants (7%) . Aphids collected from PLRV + PSTVd infected plants and stored in 70% ethanol retained PLRV beyond 42 days, but not PSTVd. Experiments with ribonuclease-treated viruliferous aphids and purified virions indicat ed some facilitation of PSTVd transmission by aphids enhanced by the p resence of PLRV but do not indicate a high percentage of transmission or a persistent nature for the PSTVd-aphid relationship.