Inside the European Plant Viroid Scenario: Continental Distribution, Host Range, and Genetic Features of the Main Viroid Populations

Viroids are a serious threat to plant health due to their broad host range, high infectivity, and latent infections. Europe's heterogeneous climate, ecology, and agriculture make it a key setting for viroid research. Despite numerous country- and host-specific reports, a continental synthesis has been lacking. In this study, we systematically collected all available official records of plant viroids in Europe from 1972 to 2025. A total of 255 documents were analyzed, encompassing 35 countries of the European continent and 118 host plant species, classified by host use (cultivated, ornamental, wild) and growth habit. Nucleotide sequences of the most common European viroids were retrieved from the NCBI database to assess genetic diversity and recombination. Europe hosts 32 of the 45 recognized viroid species worldwide (~71%), representing all eight genera. Southern Europe emerged as the main hotspot (~70% of reports), largely associated with Mediterranean climates and intensive cultivation of woody crops. Cultivated plants were the dominant hosts across all regions, while ornamentals were particularly important in Northern and Western Europe. Population genetic analyses revealed heterogeneous patterns, quasispecies dynamics, and recombination, shaped by host and geography. This is the first integrated overview of viroids across Europe, highlighting the importance of surveillance, sequencing, and genomic research.