Analysis of Viroid Replication Following Agrobacterium-mediated Inoculation of Non-host Species with Potato Spindle Tuber Viroid cDNA

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Abstract
Eight plant species that were believed to be resistant to mechanical inoculation with potato spindle tuber viroid (PSTV) were inoculated with virulent Agrobacterium tumefaciens strains the recombinant Ti plasmids of which contained infectious dsDNA copies of PSTV. PSTV-related RNAs (including its circular and linear forms) were detected in galls and roots of the six species which developed crown galls; those which did not (Zea mays and Phaseolus vulgaris) did not contain detectable levels of PSTV-related RNA. None of the eight species contained detectable PSTV-related RNA in their foliage. Although PSTV appears to be stable and to be translocated in non-hosts, analysis of RNase-resistant dsRNA preparations from Agrobacterium-inoculated sunflower suggests that PSTV does not undergo normal RNA-directed replication. Agrobacterium-mediated inoculation of Solanum acaule accession OCH11603 was followed by the appearance of PSTV in the foliage, suggesting that the previously reported resistance of this plant to PSTV infection is actually resistance to mechanical inoculation rather than immunity to infection.