Peach Latent Mosaic Viroid in Infected Peach

Within the family Avsunviroidae, encompassing viroids that replicate in plastids through a rolling-circle mechanism involving hammerhead ribozymes, peach latent mosaic viroid (PLMVd) is the type member of genus Pelamoviroid. With a size varying ranging from 335 to 351. nt, due to the presence of an insertion in some sequence variants, PLMVd adopts a branched conformation stabilized by a kissing-loop interaction in the plus strand. Most PLMVd infections in peach are symptomless, although certain PLMVd isolates induce leaf mosaics/blotches and albinism (peach calico, PC), fruit deformations and discolorations, delays in foliation, flowering, and ripening, and reduced longevity. Small (21. nt) viroid-derived RNAs containing the 12-14. nt insertion that characterizes PC-inducing isolates most likely cause PC by guiding cleavage of a host mRNA as predicted by RNA silencing. PLMVd, which has been detected in the major peach-growing areas worldwide, is transmitted by infected propagation material, pruning tools, aphids, and pollen, but not by seeds.