Hop Stunt Viroid Strains from Dapple Fruit Disease of Plum and Peach in Japan

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Abstract
Viroids have been isolated from plum trees (Prunus salicina Lindley) affected with plum dapple fruit disease and from peach trees (Prunus persica Batsch) showing dapple fruit symptoms. The viroids were inoculated mechanically to cucurbitaceous plants, in which symptoms typical of hop stunt viroid (HSV) infection appeared. The complete nucleotide sequences of an isolate from plum and an isolate from peach (AF isolate) were shown to be identical, consisting of 297 nucleotides with a 93.6% sequence homology to HSV-hop. Another isolate from peach (A9 isolate) also consists of 297 nucleotides, but the sequence homology to HSV-hop is 99.7%, showing only one nucleotide replacement. These results indicate that these three viroids are strains of HSV, which we designate HSV-plum, HSV-peach (AF) and HSV-peach (A9), respectively. Comparative analysis of the nucleotide sequences of HSV strains from hop, grapevine, citrus, cucumber, plum and peach revealed variable and conserved regions in the HSV molecule. In Japan, these viroids are closely related not only to dapple fruit disease in plum cv. Taiyo, but also to dapple fruit symptoms on peach cv. Asama-Hakutou.