Detection of Tobacco Rattle Virus RNA in Processed Potato Chips Displaying Symptoms of Corky Ringspot Disease

In Apr. 2008, commercially purchased processed potato chips were observed with dark brown arcs and rings typical of corky ringspot disease. This disease is caused by infection with tobacco rattle virus (TRV). A portion of RNA 1 of TRV was amplified by reverse transcription polymerase chain reaction (RT-PCR) from each of eight discolored chips from three different bags purchased at three locations. Sequence analysis of the 463-bp amplicons confirmed that the products were indeed TRV in origin and were 97% identical to TRV sequences of isolates originating in Washington, Florida, and Wisconsin. Extracts from the symptomatic RT-PCR-positive chips were not infectious when mechanically inoculated onto tobacco leaves. To the author's knowledge, this is the first report of the detection of plant virus RNA in a food product after high-temperature frying.

First Report of the Stubby-Root Nematode, Paratrichodorus teres, from Potato in the Columbia Basin of Washington State

Stubby-root nematodes of the genus Paratrichodorus are migratory ectoparasites that cause stunted and deformed roots. They also transmit Tobacco rattle virus, the causal agent of corky ringspot disease in potato. Thus, they are important to the potato industry in the Pacific Northwest, including the Columbia Basin of Washington state, which is one of the largest potato-producing regions in the United States. Stubby-root nematode species are difficult to identify because the morphological differences between the species are very small (4). Paratrichodorus teres is a morphologically similar species and has been reported mainly from temperate regions within Europe. P. teres has also been reported in potato fields in eastern Oregon (3). The morphological similarity between P. allius and P. teres creates problems for routine identification because trichodorid species have a conservative morphology and are separated by the following primary characteristics: females, type of genital system and vulva position; males, number of ventromedian precloacal supplements and cervical papillae and habitus (2). As with most soil nematodes, females are more prevalent than the males. Unfortunately, in the generic key (2), female P. allius and P. teres belong to subgroup 1–12 and are separated by a secondary characteristic, vaginal shape that could be affected by fixation or handling. Male P. allius and P. teres are separated by the former species having one fewer ventromedian precloacal supplement. Thus, the morphological similarity between P. allius and P. teres creates problems for routine identification. This might be one of the reasons that P. teres has not been diagnosed in Washington until now. Using nematode morphological diagnostic keys (1,2) and comparing 18S rDNA sequence data obtained from specimens with those listed on public sequence databases, e.g., NCBI GenBank, stubby-root nematodes from two potato fields close to Moses Lake, Grant County, WA, were diagnosed as P. teres. The two adjacent potato fields are irrigated and are situated approximately 100 miles from the eastern Oregon site where P. teres was first described (3). Soil samples were collected from several Columbia Basin potato fields that had corky ringspot disease and stubby-root nematodes. Corky ringspot disease is an emerging disease in Washington, and the presence of a new viruliferous nematode species might be of concern to the potato industry. References: (1) W. Decraemer. Page 615 in: Manual of Agricultural Nematology. W. R. Nickle, ed. Marcel Dekker, Inc., New York, 1991. (2) W. Decraemer and P. Baujard. Fundam. Appl. Nematol. 21:37, 1998. (3) H. J. Jensen et al. Plant Dis. Rep. 58:269, 1974. (4) S. MacFarlane et al. Adv. Bot. Res. 36:169, 2002.