First report of Tomato torrado virus on tomato from Australia

Abstract

Since 2005, a disease of greenhouse tomatoes has been observed in the North Adelaide Plains of South Australia. Symptoms include chlorosis and necrotic lesions on the leaves, stunted plants, and leaves that are frequently distorted. Necrotic lesions typically had a light green or yellow margin and affected areas often fell out, leaving small holes. The onset of disease was generally associated with an increase in population of the greenhouse whitefly (Trialeurodes vaporariorum). Isometric virions (25 to 30 nm) were observed by electron microscopy in partially purified extracts, but no other virion types were observed. In 2008, reverse transcription (RT)-PCR products were obtained using primers specific for RNA-1 (TR1F/TR1R) and RNA-2 (TR2F/TR2R) of Tomato torrado virus (ToTV) (1) using a fresh diseased sample (isolate 2136) and a 2005 archived, lyophilized sample (isolate 1883). Cucumber mosaic virus was not detected in these samples by RT-PCR (data not shown). The RT-PCR products were cloned and sequenced. The partial 892-bp RNA-1 consensus nucleotide (nt) sequences of isolates 1883 (GenBank Accession No. GQ844869) and 2136 (GenBank No. GQ844871) were 100% identical. The partial 573-bp RNA-2 consensus nt sequences of isolates 1883 (GenBank No. GQ844870) and 2143 (GenBank No. GQ844872) were 99.8% identical. The partial RNA-1 and -2 nt sequences of isolate 1883 were 99.1% and 98.5% identical to the published ToTV sequences (RNA-1, GenBank No. DQ388879; RNA-2, GenBank No. DQ88880), respectively (2). For isolate 2136, the identities were 98.1 and 98.7%, respectively. The putative amino acid sequences were all 100% identical to the published sequences. The virus was graft transmitted to tomato cv. Grosse Lisse and Datura stramonium, in which typical disease symptoms and leaf chlorosis, respectively, were induced, and by mechanical inoculation to Nicotiana benthamiana, which displayed leaf chlorosis. All inoculated plant species indexed positive by RT-PCR for ToTV. Seeds were collected from known ToTV-infected plants and the seedlings were grown in isolation in an insect-proof glasshouse. None of the seedlings exhibited symptoms of virus infection, and ToTV was not detected in 97 seedlings from cv. Beatrice, 368 seedlings from cv. Ediez, or from 286 seedlings from cv. Loretto with the virus-specific RT-PCR assays. The pathway for entry of ToTV into Australia is unknown, and although seed transmission was suspected, no evidence for this could be found. To our knowledge, this represents the first report of ToTV from Australia.