Characterization of a tymovirus causing disease in diascia ornamental plants

Two tymoviruses were isolated from Diascia hybrida 'Sun chimes"!coral' plants exhibiting chlorotic mottling of the leaves and reduced growth. The nucleotide sequence of the entire genome from one isolate was determined. The genome is 6,290 nucleotides long and contains three potential open reading frames (ORFs). The 5'-untranslated region is 154 nucleotides long and RNA folding into four hairpin structures is predicted in this region of the genome. The putative products of ORF I, II and III are 637, 1,790, and 192 amino acids, respectively. Based on homology to other tymovirus sequences, it is predicted that ORF I encodes the movement protein, ORF II the replicase and ORF III the coat protein. Secondary structure analysis of the 3'-terminus show that the RNA can form a transfer-like RNA structure that has an anticodon specific for histidine. The name Diascia yellow mottle virus (DiaYMV) is proposed for this novel virus. Based on the coat protein sequence analysis, it was revealed that the plants are also infected by a strain of the Nemesia ring necrosis virus (NeRNV). The isolate of NeRNV from Washington (NeRNV-WA) and DiaYMV share 99.5% and 94.5% amino acid sequence identity to the coat protein of NeRNV from Nemesia fruticans (NeRNV-Nf). The product of ORF II from DiaYMV shares 54.0% amino acid sequence identity with ORF II of NeRNV-Nf. When the entire genomic nucleotide sequences are compared, 77.8% identity to NeRNV-Nf is revealed; DiaYMV could not be distinguished from NeRNV by serology using a murine monoclonal antibody M3-7 A6 1 developed in this study. DiaYMV and NeRNV commonly occur in the Pacific Northwest in diascia and nemesia ornamental plants with the exception of Diascia hybrida 'Coral belle'. DiaYMV host range includes many representatives within the family Scrophulariaceae and Solanaceae with the exceptions of Datura stramonium, Chenopodium quinoa, some members of Nicotiana tabacum and members of the genus Antirrhinum. A reverse transcription-polymerase chain reaction and enzyme linked immunosorbent assay based diagnostic assays were developed for rapid detection of DiaYMV and NeRNV in nurseries. The developed diagnostic assays, however, did not discriminate between the two viruses