Tobacco rattle virus (TRV) is the type member of the tobravirus group. These viruses are transmitted by soil-inhabiting nematodes in the Trichodorus and Paratrichodorus genera (Harrison, 1970; Harrison and Robinson, 1986). The virus has a large host range, including numerous crop plants and weeds, and occurs in many parts of North America and Europe. Typically the virus is more common in soils with a sandy texture, which favors the nematode vector (Harrison, 1970). In the northwestern United States, the primary vector of TRV is P. allius (Mojtahedi et al., 2000). When the virus is transmitted to developing potato (Solanum tuberosum) tubers, internal symptoms are produced consisting of rings, arcs, and various dark blotches that may have a corky texture. Collectively, the symptoms are referred to as corky ringspot disease (CRS; Crosslin et al., 2007). If high percentages of potato tubers in a given lot show symptoms of CRS, they may be rejected by potato processors or for fresh market use, resulting in significant economic loss to the grower. Corky ringspot has been known to occur for some time in the Pacific Northwest (Mojtahedi et al., 2000), Florida, and a few other locations and was recently reported for the first time in Michigan (Kirk et al., 2008), Wisconsin, and Minnesota (Gudmestad et al., 2008).
The tobravirus genome consists of two positive sense RNA molecules. The larger RNA 1 contains four open reading frames (ORF), including those for the RNA-dependent RNA polymerase (Sudarshana and Berger, 1998). One ORF near the 3′ end of RNA 1 called the 16 kDa protein ORF codes for a factor reportedly involved in nematode transmissibility (Boccara et al., 1986) or possibly in virus gene regulation (Liu et al., 2002). Sequence analysis suggests that this ORF is highly conserved among American and European isolates of TRV and thus has been widely used for detection of the virus by reverse transcription polymerase chain reaction (RT-PCR) in potato foliage and tuber tissue (Crosslin and Thomas, 1995; Robinson, 1992; Weidemann, 1995). The smaller RNA 2 contains the capsid protein ORF and other nonstructural genes that may be involved in nematode transmission (MacFarlane, 1999). Tobacco rattle virus RNA 1 is infectious in the absence of RNA 2 but produces infections that lack capsid protein, because this gene is located on RNA 2 (MacFarlane, 1999).
Potato chips are processed by frying in vegetable oil at ≈160 °C, which would render any known plant virus inactive. Theoretically, however, the genomic RNA would be present but possibly altered by this treatment. This article reports the detection of TRV RNA in commercially purchased processed potato chips that showed symptoms typical of corky ringspot disease.
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