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Title: EVIDENCE FOR HETEROLOGOUS ENCAPSIDATION OF POTATO SPINDLE TUBER VIROID BY POTATO LEAFROLL VIRUS

Author
item QUERCI, MADDALENA - INTL POTATO CTR LIMA PERU
item Owens, Robert
item BARTOLINA, IDA - INTL POTATO CTR LIMA PERU
item LAZARTE, VIDAL - INTL POTATO CTR LIMA PERU
item SALAZAR, LUIS - INTL POTATO CTR LIMA PERU

Submitted to: Journal of General Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Viroids are the smallest known agents of infectious disease -- small, highly structured RNA molecules which lack both a protein capsid and detectable mRNA activity yet are able to replicate independently and cause disease in their plant hosts. Because viroids are readily transmitted by mechanical means (i.e., pruning, grafting, and even foliar contact), viroids pose particular threat to many vegetatively propagated crops -- potatoes, citrus, and grapes as well as several stone and pome fruits. Until now, however, convincing evidence for the transmission of potato spindle tuber (PSTVd) or other viroids by insect vectors has been lacking. Epidemiological surveys carried out with potatoes growing at three locations in China revealed a strong correlation between PSTVd infection and the presence of an aphid transmissible plant virus (i.e., potato leafroll virus), thereby suggesting that this virus can facilitate PSTVd spread under field conditions. We have also shown that (i) the common green peach aphid, Myzus persicae (Sulz.), is able to transmit PSTVd from doubly- but not singly-infected potatoes under greenhouse conditions and (ii) the viroid RNA was encapsidated within the virus particles. These results will be of greatest interest to scientists in APHIS and other organizations concerned with the safe movement of plant germplasm. Aphid transmission may greatly facilitate the spread of PSTVd (and other viroids?), thereby reducing the possibility of controlling the disease(s) which they cause.

Technical Abstract: 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 the PSTVd infection and the presence of PLRV, suggesting that PLRV can facilitate PSTVd spread under field conditions. Previous studies [Salazar et al. Fitopatologia 30(1), 56-58. 1995] have shown that the presence of PSTVd can lead to a decrease in the level of resistance of PLRV infection. Thus, elucidation of the role(s) of PSTVd in breaking down host resistance to PLRV promises to have important epidemiological and economic implications.