The hop stunt viroid is a viroid

Viroid

Viroids are plant pathogens that consist of a short stretch of highly complementary, circular, single-stranded RNA without the protein coat that is typical for viruses. The smallest discovered is a 220 nucleobase scRNA associated with the rice yellow mottle sobemovirus...

 species that infects the common hop plant, citrus plants and grapevines, among others. It is a member of the Pospiviroidae

Pospiviroidae

The Pospiviroidae are a family of viroids, including the first viroid to be discovered, PSTVd. Their secondary structure is key to their biological activity. The classification of this family is based on differences in the conserved central region sequence...

 family and the Hostuviroid

Hostuviroid

Hostuviroid is a genus of viroids that includes the hop stunt viroids, a group of viroids that infects many different types of plants, including the common hop plant.Some hostuviroids:Citrus gummy bark viroidGrapevine viroid...

 genus.
There are quite a few different sub-species of the hop stunt viroid.

Hop stunt viroids

Citrus gummy bark viroid

Citrus gummy bark viroid

The citrus gummy bark viroid is a sub-species of the hop stunt viroid, and thus is a member of the genus Hostuviroid.As the name suggests, the citrus gummy bark viroid causes problems in the bark of the sweet orange tree....

Grapevine viroid

Grapevine viroid

The grapevine viroid is a viroid that is a type of hop stunt viroid.Types of grapevine viroids:Australian grapevine viroidGrapevine yellow speckle viroid...

Dapple peach fruit disease viroid

Citrus chachexia viroid

Cucumber pale fruit viroid

Dapple plum and peach fruit disease viroid