Hop stunt viroid.

Abstract Hop stunt viroid (HSVd) was identified as the causal agent of a hop stunt disease, which first emerged in Japan in the 1960–80s, then in the United States and China in the 2000s, and in Slovenia in 2012. HSVd has a wide natural host range. Most hosts are symptomless carriers but some sensitive hosts develop cucumber pale fruit, citrus cachexia, and plum dapple fruit diseases. HSVd consists of 294–305 nucleotides. No conclusive host-determinants were found, however, a bias for the presence of certain sequences in certain hosts reflects viroid adaptation to hosts during a long history of viroid–host interactions.