IDENTIFICATION AND MOLECULAR-PROPERTIES OF A 306 NUCLEOTIDE VIROID ASSOCIATED WITH APPLE DIMPLE FRUIT DISEASE

A new viroid associated with an apple fruit disorder similar to, but m ore severe than, the dapple apple disease induced in some varieties by apple scar skin viroid (ASSVd) has been found. The new viroid, tentat ively termed apple dimple fruit viroid (ADFVd), is a circular RNA of 3 06 nucleotides which adopts a quasi-rod-like conformation of minimum f ree energy. It contains the core nucleotides of the central conserved region (CCR) of the ASSVd group as well as the terminal conserved regi on (TCR) present in all members of the ASSVd and potato spindle tuber viroid (PSTVd) monophyletic groups. ADFVd has the highest sequence sim ilarity with ASSVd and the 294 nucleotide citrus viroid CVd-IIIb, shar ing with the latter an almost identical left terminal domain. The righ t- and left-hand termini of ADFVd are formed by almost perfect duplica tions of sequences found in the CCR upper and lower strands, respectiv ely, of PSTVd and closely related viroids.