Avocado sunblotch disease: a persistent viroid infection in which variants are associated with differential symptoms.

Variants of avocado sunblotch viroid (ASBVd) of between 247 and 250 nucleotides in length have been recovered from diseased avocado tissues. The sunblotch syndrome covers a complex pattern of disease symptoms which are associated with infection by variants of ASBVd. The viroid species are designated ASBVd-B, ASBVd-V and ASBVd-Sc from their association with bleached, variegated or symptomless carrier tissues respectively. Host-viroid interactions and structural relationships among the variants suggest a transition in sunblotch disease from a severe acute to a persistent mild form of infection.