We have produced transgenic potato lines expressing the yeast-derived double-stranded RNA-specific ribonuclease pac1. Five lines of pac1 potato (Solanum tuberosum L., cultivar Russet Burbank) challenged with potato spindle tuber viroid (PSTVd) suppressed PSTVd infection and accumulation. All of the progeny potato tubers produced by resistant plants were also free of PSTVd. Because the pac1 gene product digested PSTVd in vitro, double-stranded regions in PSTVd molecule and/or replicative intermediates may be targeted by pac1 gene product in the transgenic potato plant.