Analysis of sequence variation in grapevine yellow speckle viroid 1 reveals two distinct alternative structures for the pathogenic domain.

The nucleotide sequences of 24 full-length cDNA clones prepared from a field isolate of grapevine yellow speckle viroid 1 (GYSV 1) have been determined and compared with that of the previously published GYSV 1 sequence. A large number of sequence variations were observed, the majority of which occurred in the pathogenicity domain (P domain) of the viroid. The GYSV 1 variants could be divided into two types each containing a distinct secondary structure within the P domain. Monomeric exact-length RNA transcripts produced from individual clones belonging to both types were infectious in viroid-free grapevines and produced homogenous populations of progeny viroid in vivo.