Vegetative propagation and its possible role as a genetic bottleneck in the shaping of the apple fruit crinkle viroid populations in apple and hop plants

Apple fruit crinkle viroid (AFCVd) infects apples and hops. To analyze the genetic diversity of AFCVd, nine apple and six hop isolates were collected from several locations in Japan. In total, 76 independent cDNA clones were used for sequencing and phylogenetic analyses. Two major population clusters were identified. The first consisted of all four hop isolates from Akita and some from Yamagata. The second cluster consisted of some Yamagata hop and all apple isolates. On the basis of the polymorphism found in the nucleotide insertion between positions 142/143 of the AFCVd genome and the history of hop cultivation in the region, it appears likely that one of the AFCVd populations that pre-existed in the Yamagata hops served as a “founder” for the Akita hop cluster. In this scenario, a genetic bottleneck caused by vegetative propagation played an important role in the shaping of viroid populations in a cultivated crop.