Submitted to: Temperate Fruit Crop Viruses and Virus Diseases
Publication Type: Abstract Only
Publication Acceptance Date: 9/15/1997
Publication Date: N/A
Technical Abstract: Dapple apple viroid (DAVd) is a member of the apple scar skin (ASSVd) group of viroids. Dapple apple, a fruit blemishing, graft-transmissible disease, was first described in the 1950's from an apple orchard in New Hampshire, and has subsequently been reported in other countries, including Canada, Japan, China, U.K., and Italy. DAVd and ASSVd may be distinguished by fruit symptoms on the apple cultivar "Red Delicious". The viroids infect Chinese pear cultivars without showing symptoms on infected fruits, however, they cause fruit disorders on Japanese pear cultivars. Attempts to transmit these viroids to herbaceous hosts have been unsuccessful; tranmission to woody hosts have been primarily by grafting from infected materials. In order to complete Koch's postulates and to show that DAVd is responsible for the systemic infection in infected trees, cloned dimeric copies of DAVd were inserted into a binary vector containing the CaMV35S promoter, which was subsequently introduced into Agrobacterium strain LBA4404. Seedlings of "Gala" apple and Western pear (kindly obtained from R. H. Zimmerman of Beltsville and J. Postman of Corvallis, respectively) were agroinoculated on their stems with solutions of Agrobacteria containing the plasmid pB1121:DAVd construct. Seedlings were kept in a growth chamber and monitored for viroid infection by dot blot hybridization and Northern analysis. A few seedlings of pear and apple became systemically infected with DAVd and the viroid progeny were confirmed by nucleotide sequence analysis to be identical to that of the inoculum.