Cherry chlorotic rusty spot (CCRS) and Amasya cherry disease (ACD) display similar symptoms and are associated with a series of dsRNAs. However, a direct comparison has been lacking. Here, a side-by-side analysis confirmed that both diseases were symptomatologically very similar, as were the number (10-12) and size of their associated dsRNAs. Sequence determination of four of these dsRNAs revealed that they were essentially identical for CCRS and ACD. The largest (3399 bp), which potentially encoded a protein of 1087 aa with the eight motifs conserved in RNA-dependent RNA polymerases of dsRNA mycoviruses, had the highest similarity to those coded by dsRNA 1 of viruses belonging to the genus Chrysovirus and was termed CCRS or ACD chrys-dsRNA 1. The three closely migrating dsRNAs had the properties of the other components of a chrysovirus and in CCRS and ACD versions, respectively, were chrys-dsRNA 2 (3125 and 3128 bp), chrys-dsRNA 3 (2833 bp) and chrys-dsRNA 4 (2499 and 2498 bp), potentially encoding the major capsid protein (993 and 994 aa) and two proteins (884 and 677 aa, respectively) of unknown function. The four 59-and 39-UTRs shared internal similarities and had conserved GAAAAUUAUGG and AUAUGC termini, respectively. The 59-UTRs contained the 'Box 1' motif followed by a stretch rich in CAA, CAAA and CAAAA repeats, characteristic of chrysovirus dsRNAs. Because species of the genus Chrysovirus have only been described as infecting fungi, this suggests a fungal aetiology for CCRS and ACD, a proposal supported by the properties of two other CCRS-and ACD-associated dsRNAs (see accompanying paper by Coutts et al., 2004, in this issue).

The sequence of the four large (L) double-stranded RNAs (dsRNAs) associated with Amasya cherry disease (ACD), which has a presumed fungal aetiology, is reported. ACD L dsRNAs 1 (5121 bp) and 2 (5047 bp) potentially encode proteins of 1628 and 1620 aa, respectively, that are 37 % identical and of unknown function. ACD L dsRNAs 3 (4458 bp) and 4 (4303 bp) potentially encode proteins that are 68 % identical and contain the eight motifs conserved in RNA-dependent RNA polymerases (RdRp) of dsRNA mycoviruses, having highest similarity with those of members of the family Totiviridae. Both terminal regions share extensive conservation in all four RNAs, suggesting a functional relationship between them. As ACD L dsRNAs 1 and 2 do not encode RdRps, both are probably replicated by those from either ACD L dsRNA 3 or 4. Partial characterization of the equivalent L dsRNAs 3 and 4 associated with cherry chlorotic rusty spot revealed essentially identical sequences.

Short CommunicationCherry chlorotic rusty spot and Amasya cherry diseases are associated with a complex pattern of mycoviral-like double-stranded RNAs. II.

No abstract

No abstract