Differential Symptom Development and Viral RNA Loads in 10 Accessions Infected with the Tobamovirus Yellow Tailflower Mild Mottle Virus.

Yellow tailflower mild mottle virus (YTMMV, genus ) was identified from wild plants of solanaceous species in Australia. is a species indigenous to the arid north of Australia. accession RA-4 (the lab type), which has a mutant, functionally defective, RNA-dependent RNA polymerase 1 () gene (), has played a significant role in plant virology, but little study has been done regarding responses to virus infection by other accessions of . All wild-collected accessions used in this study harbored wild-type genes (). We compared symptoms of YTMMV infection and viral RNA load on RA-4 and nine wild-collected accessions of from mainland Western Australia, an island, and the Northern Territory. After inoculation with YTMMV, RA-4 plants responded with systemic hypersensitivity and all individuals were dead 35 days postinoculation (dpi). Plants of wild-collected accessions exhibited a range of symptoms, from mild to severe, and some, but not all, died in the same period. Quantitative reverse transcription PCR revealed that the mutation was not a predictor of viral RNA load or symptom severity. For example, wild-collected A019412 plants carried more than twice the viral RNA load of RA-4 plants, but symptom expression was moderate. For plants of most accessions, viral RNA load did not increase after 10 dpi. The exception was plants of accession Barrow-1, in which viral RNA load was low until 15 dpi, after which it increased more than 29-fold. This study revealed differential responses by accessions to infection by an isolate of YTMMV. The gene, whether mutant or wild-type, did not appear to influence viral RNA load or disease expression. Genetic diversity of the 10 accessions in some cases reflected geographical location, but in other accessions this was not so.