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Title: Characterization of Resistance to Corky Ringspot Disease in Potato: A Case for Resistance to Infection by Tobacco Rattle Virus

item Brown, Charles - Chuck
item Mojtahedi, Hassan
item Crosslin, James
item JAMES, S
item NOVY, R
item LOVE, S
item VALES, M
item HAMM, P

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2008
Publication Date: 1/15/2009
Citation: Brown, C.R., Mojtahedi, H., Crosslin, J., James, S., Charlton, B., Novy, R., Love, S., Vales, M.I., Hamm, P. 2009. Characterization of Resistance to Corky Ringspot Disease in Potato: A Case for Resistance to Infection by Tobacco Rattle Virus. American Journal of Potato Research. 86:49–55

Interpretive Summary: Crops are subject to attack by pests and pathogens. The disease of potato called Corky Ringspot Disease is due to the cooperation of a virus and small worm in the soil. The worm has a sharp mouthpart that pierces the roots and obtains sustenance from the plant. However, while doing this the worm can take up a certain kind of virus that spends most of its time in the root tissue. The worm goes on to feed on other roots while carrying its load of virus. Although the worm gets no benefit from this errand that we know of, the virus requires this hitchhiking arrangement to move from plant to plant. When the worm with virus feeds on a developing potato underground, the virus is inserted and causes a dark colored blemish which is called corky ringspot due to its cork-like appearance in the diseased potato flesh. Although farmers use costly soil fumigants to control the nematode and prevent virus transmission, the presence of virus and nematodes is a serious risk to the farmer. Resistance in newly bred potato varieties is one way to handle it without chemicals. In this study we found that potatoes that do not get the disease have resistance to invasion by the virus. We found this by using a sensitive test to look for the virus. In most of the different breeding lines we tested we did not find any indication of virus, while susceptible cutlivars showed corky ringspot symptoms and the test found virus. Breeding of potato varieties resistant to corky ringspot will result in the use of less soil fumigant and increase the profitability of potato farming.

Technical Abstract: Corky ringspot disease (spraing) is incited by the transmission of tobacco rattle virus by stubby root nematode (Paratrichodorus spp.). The resulting damage consists of internal and skin surface necrotic blemishes which render the tubers unmarketable. Resistance to the disease has been extensively documented in breeding programs. High levels of resistance are known for a number of varieties and breeding lines. Because tubers that are symptomless but virus infected have been documented the nature of resistance is a point of debate. In two field locations where a total of 1259 tubers of resistant breeding lines were RT-PCR tested, 5.6 and 2.0 percent of symptomless tubers gave positive PCR tests in the different fields. Nearly all of these were from three clones that would have been classified as susceptible by symptoms in later testing. Taken as a whole 58 percent of the symptomatic were accompanied by positive PCR tests. Standard commercial susceptible cultivars showed 34 percent symptomless tubers with positive PCR results. We have shown here that most resistant lines are not positive for the virus when asymptomatic tubers are tested by RT-PCR. Symptomatic tubers are mostly positive. Within selected resistant materials, clones with the highest level of asymptomatic positives also showed susceptible responses as assessed by visual ranking in later tests. Although RT-PCR is unable to amplify from symptomatic tubers in some cases, the results of this study suggest that most resistant breeding lines positive do not test positive as latent carriers of the virus.