Detection and Molecular Characterization of Peach Latent Mosaic Viroid Isolates Infecting Stone Fruit Trees in Poland

Field surveys were carried out to assess the incidence of peach latent mosaic viroid in nine orchards of stone fruit trees in four growing regions of Poland. Forty of 119 peaches, six of 37 apricots, five of eight nectarines and one of four plums trees tested positive by RT-PCR for this viroid. Most of the infected stone fruit trees did not show any symptoms. Leaf yellow mosaic was only noticed on ‘Maycrest’ peach and ‘Saturn’ nectarine trees, and additional symptoms of cracked fruits with corky sutures and enlarged pits were observed on one ‘Maycrest’ tree. One or two isolates from each orchard and each species of infected tree were selected, and together, 11 isolates of peach latent mosaic viroid were used for genetic analyses. The nucleotide sequence similarity of selected isolates found in Poland was 93.6–100%. They shared 82.0–98.8% similarity with the viroid strains from different hosts and geographical regions. The phylogenetic analysis led to the clustering of all isolates detected during this study in the most numerous represented subgroup II-A, composed of peach latent mosaic viroid strains originating from different geographic regions and host plants. Although Polish isolates were clustered in the same subgroup, some differed in length and nucleotide sequences. It was shown that the genetic variability of isolates found in Poland was unrelated to the regions of their origin. A positive signal was obtained in dot-blot hybridization of all analyzed 11 isolates.