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Tobacco Rattle Virus (TRV) – Biology

TRV was first discovered in Germany in 1931 and first reported as corky ringspot of potato in Florida in 1946. The disease is found on every continent. In North America TRV has been detected in California, Colorado, Florida, Indiana, Idaho, Michigan, Minnesota, North Dakota, Oregon, Washington and Wisconsin.

TRV has a very wide host range, infecting over 400 species. Some hosts of TRV include vegetables like beans, beets, peppers, and spinach; ornamentals such as daffodils, sunflower, and tulips; and weeds like hairy nightshade and chickweed (see list of common hosts on the TRV Management page). Many hosts do not develop symptoms.

TRV is transmitted by several species of stubby-root nematodes in the genera Paratrichodorus and Trichodorus. Nematodes are microscopic-worm like organisms that inhabit many ecosystems. Stubby root nematodes inhabit the soil where they feed on roots of susceptible hosts. This feeding causes the roots to cease growing, hence the name “stubby root”. All life stages occur in the soil, including the egg and four larval stages. Stubby root nematodes are highly mobile in the soil and can travel vertically to depths of 40 inches. Although nematode populations decline quickly after plants are removed from the field and temperatures drop, enough survive by migrating below the frost line or becoming dormant to trigger a new epidemic in the following year. Nematode populations are highest in the fall, so harvesting early may result in some reduction of disease. While these nematodes are not considered harmful to potato plants on their own, they are a serious threat to potato production because they introduce and spread TRV when feeding on plant roots. Unfortunately, only a few nematodes can cause a high incidence of disease.

A number of nematicides and fumigants are effective in controlling or suppressing stubby root nematodes. Oxamyl (Vydate™) applied at planting and chemigated post-emergence applications can provide good control of stubby root nematodes and suppress TRV infection if applied at the appropriate intervals during the growing season. Applications of fluopyram (Velum Prime ™) followed by post-emergence applications of spirotetramat (Movento ™) have been demonstrated to provide suppression of stubby root nematodes. Fall fumigation prior to planting with 1,3 dichloropropene (Telone™) can reduce stubby root nematode populations. Growers are encouraged to seek advice from their local university extension personnel for more specific information on application timing and chemical rates. However, none of these treatments are a guarantee of adequate control because stubby-root nematodes can escape the chemicals by penetrating deep in the soil. Managing stubby-root nematodes through crop rotation is difficult because the nematodes feed on a wide range of plant species.

Environmental conditions that favor nematode development and movement increase spread of the virus. High soil moisture allows the nematodes to move easily to new plant hosts and access roots for feeding. Moderately warm temperatures increase the nematode population by speeding up their reproductive cycle. Under ideal conditions, stubby-root nematodes can produce several generations per year so large populations can develop rather quickly. As nematode populations increase in a field, the virus will be disseminated more easily. TRV transmission is limited in dense soils containing high proportions of clay, silt, or very fine sand as the nematodes have difficulty penetrating these types of soils.

TRV is spread in infected tubers, true seeds, plant debris as well as on contaminated tools. Strict sanitary practices should be used when working with infected plants. Knives or other tools used for pruning or cutting tuber pieces must be decontaminated often. Stubby root nematodes are spread in infested plant debris and soil.

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