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 nu cleotides in length have been recovered from diseased avocado tissues. The sunblotch syndrome covers a complex pattern of disease symptoms w hich are associated with infection by variants of ASBVd. The viroid sp ecies are designated ASBVd-B, ASBVd-V and ASBVd-Sc from their associat ion with bleached, variegated or symptomless carrier tissues respectiv ely. Host-viroid interactions and structural relationships among the v ariants suggest a transition in sunblotch disease from a severe acute to a persistent mild form of infection.